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The effects of disease-related mortality of young-of-year smallmouth bass on population characteristics in the Susquehanna River Basin, Pennsylvania and potential implications to conservation of black bass diversity
Abstract
In recent years, wide-scale mortality of young-of-year (YOY) Smallmouth
Bass Micropterus dolomieu has affected recruitment in the Susquehanna River and a number
of its tributaries. Investigations have determined that these mortality events are associated with
changes in various components of water quality in the presence of multiple pathogens. Outbreaks
have been characterized by lesions colonized by several species of bacteria, including
motile Aeromonas spp., Flavobacterium columnaris, and Pseudomonas aeruginosa. Further,
the myxozoan parasite Myxobolus inornatus and trematode metacercariae have been documented
in affected fish. Many of the specimens submitted for analysis have also been infected
by Largemouth Bass virus. However, the relationship between any particular pathogen and
the mortalities remains unclear. Histological analysis of adult bass has demonstrated frequent
and severe cases of intersex (i.e., testicular oocytes) and measurable plasma concentrations
of vitellogenin in male Smallmouth Bass, suggesting the presence of endocrine-disrupting
compounds in the system. It is uncertain what compounds are present or how these compounds
may contribute to immunosuppression of YOY Smallmouth Bass, allowing for bacterial and
parasite colonization. A complex relationship of several, sublethal stressors are contributing to
repeated occurrence of disease outbreaks. Although the Smallmouth Bass is not native to the
Susquehanna system, it could be used as a case study as to how changes in water quality and
multiple pathogens could pose a threat to conservation of populations of black bass species
with low densities and limited distribution.
... The discovery of M. Inornatus in Susquehanna River YOY smallmouth bass was one of many stressors identified as potential risk factors for YOY disease and mortality (Smith, Blazer, Walsh, Iwanowicz, & Sperry, 2015;Walsh et al., 2018). Multiple pathogens and parasites have been identified including bacteria (e.g., multiple aeromonads, Flavobacterium columnare (Bernardet and Grimont); Starliper, Blazer, Iwanowicz, & Walsh, 2014), largemouth bass virus (Boonthai et al., 2018;Smith et al., 2015;Starliper et al., 2014), trematodes (Smith et al., 2015) and cestodes . In addition to pathogens and parasites, water quality concerns including elevated water temperatures, suboptimal dissolved oxygen concentrations and contaminants have also been investigated in regard to the overall health of YOY smallmouth bass in the Susquehanna River Basin Chaplin, Crawford, & Brightbill, 2009;Smith et al., 2015;Walsh et al., 2018 ...
... The discovery of M. Inornatus in Susquehanna River YOY smallmouth bass was one of many stressors identified as potential risk factors for YOY disease and mortality (Smith, Blazer, Walsh, Iwanowicz, & Sperry, 2015;Walsh et al., 2018). Multiple pathogens and parasites have been identified including bacteria (e.g., multiple aeromonads, Flavobacterium columnare (Bernardet and Grimont); Starliper, Blazer, Iwanowicz, & Walsh, 2014), largemouth bass virus (Boonthai et al., 2018;Smith et al., 2015;Starliper et al., 2014), trematodes (Smith et al., 2015) and cestodes . In addition to pathogens and parasites, water quality concerns including elevated water temperatures, suboptimal dissolved oxygen concentrations and contaminants have also been investigated in regard to the overall health of YOY smallmouth bass in the Susquehanna River Basin Chaplin, Crawford, & Brightbill, 2009;Smith et al., 2015;Walsh et al., 2018 ...
... Multiple pathogens and parasites have been identified including bacteria (e.g., multiple aeromonads, Flavobacterium columnare (Bernardet and Grimont); Starliper, Blazer, Iwanowicz, & Walsh, 2014), largemouth bass virus (Boonthai et al., 2018;Smith et al., 2015;Starliper et al., 2014), trematodes (Smith et al., 2015) and cestodes . In addition to pathogens and parasites, water quality concerns including elevated water temperatures, suboptimal dissolved oxygen concentrations and contaminants have also been investigated in regard to the overall health of YOY smallmouth bass in the Susquehanna River Basin Chaplin, Crawford, & Brightbill, 2009;Smith et al., 2015;Walsh et al., 2018 ...
A myxozoan parasite, Myxobolus inornatus, is one disease agent identified in young of the year (YOY) smallmouth bass in the Susquehanna River Basin, Pennsylvania. We investigated spatial and temporal variability in M. Inornatus prevalence across the Susquehanna River Basin and at several out‐of‐basin sites. We examined potential land use drivers of M. Inornatus prevalence including agricultural and developed land use. In 1,267 YOY smallmouth bass collected from 32 sites during 2013–2016, M. Inornatus was documented in 43.6% of samples. Among‐site variability in parasite prevalence was greater than among‐year variability. The effect of agricultural land use on M. Inornatus prevalence had a high probability of being positively correlated at multiple spatial scales (probability of positive effect > 0.80). The effect of developed land use on M. Inornatus prevalence had a relatively high probability of being negatively correlated at multiple spatial scales (probability of negative effect > 0.70). Our results suggest that land use practices could be related to M. Inornatus infection of smallmouth bass. Further study will be necessary to determine whether disease dynamics are a consequence of effects on the host, alterations of instream habitat mediating invertebrate host dynamics and/or survival and dispersal of the parasite infective stage.
... While disease has a large impact on YOY smallmouth bass, it appears to have little if any effect on other species. Pathological analysis has indicated that bacterial infections by Flavobacterium columnare (columnaris), Aeromonas allosaccarophila, A. hydrophila, A. popoffii, A. veronii-sobria biovar, A. veronii-veronii biovar, and Pseudomonas aeruginosa are responsible for disease and mortality (Chapin et al. 2009;Chapin and Crawford 2012;Starliper et al. 2014;Smith et al. 2015). All are opportunistic bacteria so the mechanism of infection is similar despite species differences. ...
... Effects of disease, in conjunction with the typical variables that drive population characteristics, can manifest into population-level issues. This is especially true when they affect survival and recruitment (Smith et al. 2015). Reproduction and recruitment of smallmouth bass to river fisheries is highly variable across Pennsylvania rivers and other rivers across the country Pflieger 1975;Paragamian 1984;Slipke et al. 1998;Buynak and Mitchell 2002;Swenson et al. 2002;Smith et al. 2005). ...
... Despite variability in reproduction and recruitment, regression residual technique analysis demonstrated that large year classes exposed to disease exhibited survival that was below average relative to those not exposed both within and outside the incident area and time . Periodic boat electrofishing relative abundance estimates (catch per unit effort, CPUE, fish/h) of adult smallmouth bass have demonstrated a significant decrease in relative abundance between pre-2005 and post-2005 periods (Smith et al. 2015; Figure 2). Further, the length distribution-used, in this instance, as a surrogate measure of age-of smallmouth bass is different as a result of changes in recruitment at this reach. ...
... River systems, occurring annually to varying degrees, than in the Allegheny and other drainages. These SMB die-offs have created considerable concerns among the sportfishing industry, as well as in state and federal agencies, as decreases in relative abundance of YOY and adult SMB and shifts in size structure have concurrently been noticed [1]. Affected SMB exhibited exophthalmia, dermal lesions (e.g., fin erosions and rounded, shallow ulcers), and organomegaly. ...
... Affected SMB exhibited exophthalmia, dermal lesions (e.g., fin erosions and rounded, shallow ulcers), and organomegaly. The prevalence of moribund fish varied both spatially and temporally and was most prevalent during years with high water temperatures [1]. Several fish-pathogenic bacteria and parasites were reported from fish collected during the course of mortality episode examinations, such as Aeromonas spp., Shewanella putrefaciens, Flavobacterium columnare, Pseudomonas aeruginosa, myxozoa (e.g., Myxobolus inornatus) and trematodes [1][2][3][4]. ...
... The prevalence of moribund fish varied both spatially and temporally and was most prevalent during years with high water temperatures [1]. Several fish-pathogenic bacteria and parasites were reported from fish collected during the course of mortality episode examinations, such as Aeromonas spp., Shewanella putrefaciens, Flavobacterium columnare, Pseudomonas aeruginosa, myxozoa (e.g., Myxobolus inornatus) and trematodes [1][2][3][4]. Largemouth bass virus (LMBV, genus Ranavirus, Family Iridoviridae) has also been isolated from both apparently healthy and moribund SMB during fish-kill episodes in several river watersheds in Pennsylvania (4, https://www.fws.gov/wildfishsurvey/) and the Chesapeake Bay watershed [5]. The contributions of each of these pathogens (single or combined) in causing these recurrent SMB kills have not been thoroughly investigated under controlled laboratory conditions. ...
Background:
Mortality episodes have affected young-of-year smallmouth bass (Micropterus dolomieu) in several river systems in Pennsylvania since 2005. A series of laboratory experiments were performed to determine the potential role of largemouth bass virus (Ranavirus, Iridoviridae) in causing these events.
Results:
Juvenile smallmouth bass experimentally infected with the largemouth bass virus exhibited internal and external clinical signs and mortality consistent with those observed during die-offs. Microscopically, infected fish developed multifocal necrosis in the mesenteric fat, liver, spleen and kidneys. Fish challenged by immersion also developed severe ulcerative dermatitis and necrotizing myositis and rarely panuveitis and keratitis. Largemouth bass virus-challenged smallmouth bass experienced greater mortality at 28 °C than at 23 or 11 °C. Co-infection with Flavobacterium columnare at 28 °C resulted in significant increase in mortality of smallmouth bass previously infected with largemouth bass virus. Aeromonas salmonicida seems to be very pathogenic to fish at water temperatures < 23 °C. While co-infection of smallmouth bass by both A. salmonicida and largemouth bass virus can be devastating to juvenile smallmouth bass, the optimal temperatures of each pathogen are 7-10 °C apart, making their synergistic effects highly unlikely under field conditions.
Conclusions:
The sum of our data generated in this study suggests that largemouth bass virus can be the causative agent of young-of-year smallmouth bass mortality episodes observed at relatively high water temperature.
... Specifically, the proportional stock density (PSD) of SMB, a measure of balance in freshwater fish populations which compares the proportions of larger, quality length fish (280 mm TL) to stock length fish (180 mm TL; Anderson and Weithman 1978), increased in the post-2005 time period (Figure 2). Pre-2005 PSD values for the middle Susquehanna River were considered optimal at approximately 30 – 40% (Weiss-Glanz and Stanley 1984); post-2005 PSD values for the middle Susquehanna River increased to 35% -65% (Smith et al. 2015). The post-2005 PSD suggested that there were a limited number of smaller or younger fish in the population and that rates of reproduction, growth, and mortality were no longer reflective of a healthy and stable population. ...
... During the first few months of life, a critical period for survival and development of SMB, YOY occupy near-shore riverine microhabitats characterized by relatively slow-moving and shallow water (Chaplin and Crawford 2012). Decreased quality and quantity of YOY habitat from factors such as high flow, increased algal growth, low DO concentration, high concentration of suspended solids, and high temperatures could result in direct mortality or increased susceptibility of YOY to disease (Smith et al. 2015). ...
... As described in the introduction, a high frequency of disease associated with pathogen and parasite infections has been noted in YOY SMB since 2005 (Figure 7). Pathological analysis indicated that the disease was caused by secondary infections by opportunistic bacteria (e.g., Flavobacterium columnare, Aeromonas hydrophila) (Smith et al. 2015). As secondary pathogens, these organisms do not typically kill fish directly but manifest as a result of another factor affecting immune function.Figure 7. The number of years YOY SMB were collected with obvious signs of disease (lesions, fin erosions, or dead individuals) during backpack electrofishing surveys at major river and warm-water stream locations in Pennsylvania. ...
Unusual mortality events of smallmouth bass (SMB) have been observed in the Susquehanna River Basin annually since 2005 and have coincided with a decline in recruitment of young-of-year fish into the adult SMB population. In 2014, the Pennsylvania Department of Environmental Protection (PADEP) in cooperation with the Pennsylvania Fish and Boat Commission (PFBC) initiated an effort to synthesize the large body of potentially relevant publications, data, and analyses. U.S. EPA’s stressor identification process (CADDIS (www.epa.gov/caddis)) was selected for the assessment because it provides transparency and reduces bias without restricting the types of evidence used. Over 50 analytical worksheets comprising almost 400 pages describing data collections and analyses were developed and evaluated by experts over the course of three workshops. The causal assessment successfully narrowed the scope of concerns and will be used to guide future studies and management of the Susquehanna and Juniata Rivers.
... The nearby Susquehanna River watershed in Pennsylvania supports an economically important, although introduced, SMB population. Health issues, including mortality events of young-of-year (Smith et al., 2015;Walsh et al., 2018), as well as skin lesions , a high prevalence of intersex (testicular oocytes; TO), and other signs of exposure to endocrine disrupting contaminants in adults (Blazer et al., 2014a) have been observed there. These have not only raised concerns of resource managers and the public but have also been associated with population declines (Schall et al., 2018a;Smith et al., 2015). ...
... Health issues, including mortality events of young-of-year (Smith et al., 2015;Walsh et al., 2018), as well as skin lesions , a high prevalence of intersex (testicular oocytes; TO), and other signs of exposure to endocrine disrupting contaminants in adults (Blazer et al., 2014a) have been observed there. These have not only raised concerns of resource managers and the public but have also been associated with population declines (Schall et al., 2018a;Smith et al., 2015). To date, no single cause for the health anomalies has been identified; rather, poor water quality, complex mixtures of contaminants, and various pathogens and parasites have been identified as potential risk factors (Boonthai et al., 2018;Schall et al., 2018b;Walsh et al., 2018). ...
Smallmouth bass Micropterus dolomieu were sampled from three sites within the Lake Erie drainage (Elk Creek, Twentymile Creek, and Misery Bay, an embayment in Presque Isle Bay). Plasma, tissues for histopathological analyses, and liver and testes preserved in RNALater® were sampled from 30 smallmouth bass (of both sexes) at each site. Liver and testes samples were analyzed for transcript abundance with Nanostring nCounter® technology. Evidence of estrogenic endocrine disruption was assessed by the presence and severity of intersex (testicular oocytes; TO) and concentrations of plasma vitellogenin in male fish. Abundance of 17 liver transcripts associated with reproductive function, endocrine activity, and contaminant detoxification pathways and 40 testes transcripts associated with male and female reproductive function, germ cell development, and steroid biosynthesis were also measured. Males with a high rate of TO (87–100%) and plasma vitellogenin were noted at all sites; however, TO severity was greatest at the site with the highest agricultural land cover. Numerous transcripts were differentially regulated among the sites and patterns of transcript abundance were used to better understand potential risk factors for estrogenic endocrine disruption. The results of this study suggest endocrine disruption is prevalent in this region and further research would benefit to identify the types of contaminants that may be associated with the observed biological effects.
... Observations of age-0 Smallmouth Bass mortalities were first documented in the summer of 2005 and have varied in prevalence and spatially and temporally in years since (Walsh et al. 2018). The magnitude of reoccurring disease in age-0 Smallmouth Bass has been observed at the population level, with a significant decrease in age-1 Smallmouth Bass and a shift to larger and older fish (Smith et al. 2015). Initial observations from randomly sampled and/or moribund fish with visible skin lesions included the myxozoan parasite Myxobolus inornatus (Walsh et al. 2012a) as well as Flavobacterium columnare (Chaplin et al. 2009). ...
... Subsequently, Largemouth Bass virus (LMBV), other parasites, and multiple Aeromonas spp. were identified (Starliper et al. 2013;Smith et al. 2015;Boonthai et al. 2018;Walsh et al. 2018). Abiotic factors such as water quality, contaminants of emerging concern, and periods of increased water temperature may also be associated with disease, but it is likely the cumulative effects of these stressors that present the greatest risk. ...
Histopathological assessments of young‐of‐the‐year (age‐0) Smallmouth Bass Micropterus dolomieu in the Susquehanna River drainage identified a high prevalence of the myxozoan Myxobolus inornatus. This myxozoan infects the connective tissue of the muscle below the skin but is sometimes observed in the esophagus and buccal cavity. In some instances, shallow infections cause breaks in the skin, which could increase the chance of opportunistic bacterial infections. Several microbial pathogens, including Flavobacterium columnare, Aeromonas spp., and Largemouth Bass virus, have also been cultured from clinically diseased young of year. A multiplex fluorescence in situ hybridization (FISH) assay was developed to determine potential colocalization of M. inornatus, Flavobacterium spp., and Aeromonas spp. infections. With FISH, 75% of age‐0 Smallmouth Bass exhibited M. inornatus infections, 10% had Aeromonas spp. infections, and 5% had Flavobacterium spp. infections, while 3% had coinfections with both bacterial species and M. inornatus. The results of the multiplex FISH assay revealed a low occurrence of coinfections of Flavobacterium spp. and/or Aeromonas spp. with M. inornatus in randomly sampled individuals.
... Although, the risk of these contaminants to aquatic life is still uncertain, there is concern that exposure to contaminants and contaminant mixtures may have negative populationlevel effects on some fisheries (Hamilton et al., 2016;Martin and Grant, 2019). For example, starting in the early 2000's, there have been signs of reproductive endocrine disruption, clinical signs of disease, declines in catch rates and mortality events in smallmouth bass (Micropterus dolomieu) populations (Arway and Smith, 2013;Kolpin et al., 2013;Blazer et al., 2014;Smith et al., 2015;Schall et al., 2018;Walsh et al., 2018). Over this same time period, several studies detected chemicals in surface waters that could represent a risk to aquatic biota. ...
... Further, it is interesting that in our study the occurrence of total estrogenicity was not greatly affected by changes in stream discharge, though this lack of effect of stream discharge does not illustrate the potential effects of discharge on the magnitude of the total estrogenic activity in the water column. Understanding the environmental drivers of estrogenic activity in surface water is important because research suggests that exposure to endocrine disrupting compounds can have negative impacts on disease resistance and immunity of fishes (Iwanowicz and Ottinger, 2009;Milla et al., 2011) leading to increased disease (Blazer et al., 2010;Walsh et al., 2018) which may ultimately lead to declines in abundance due to low recruitment (Arway and Smith, 2013;Smith et al., 2015). ...
Investigating the spatiotemporal dynamics of contaminants in surface water is crucial to better understand how introduced chemicals are interacting with and potentially influencing aquatic organisms and environments. Within the Chesapeake Bay Watershed, United States, there are concerns about the potential role of contaminant exposure on fish health. Evidence suggests that exposure to contaminants in surface water is causing immunosuppression and intersex in freshwater fish species. Despite these concerns, there is a paucity of information regarding the complex dynamics of contaminant occurrence and co-occurrence in surface water across both space and time. To address these concerns, we applied a Bayesian hierarchical joint-contaminant model to describe the occurrence and co-occurrence patterns of 28 contaminants and total estrogenicity across six river sites and over three years. We found that seasonal occurrence patterns varied by contaminant, with the highest occurrence probabilities during the spring and summer months. Additionally, we found that the proportion of agricultural landcover in the immediate catchment, as well as stream discharge, did not have a significant effect on the occurrence probabilities of most compounds. Four pesticides (atrazine, metolachlor, fipronil and simazine) co-occurred across sites after accounting for environmental covariates. These results provide baseline information on the contaminant occurrence patterns of several classes of compounds within the Chesapeake Bay Watershed. Understanding the spatiotemporal dynamics of contaminants in surface water is the first step in investigating the effects of contaminant exposure on fisheries and aquatic environments.
... Equally, Watson et al. [155] showed that water temperature had a significant effect on the increase in white sturgeon iridovirus (WSIV) disease outbreaks in juvenile white sturgeon in which mortality was higher during high temperatures. Wolf [156] showed that when the water temperature was maintained at 25 • C, symptoms caused by iridovirus infections in Centrarchidae lasted 10 days but were less pronounced for several weeks when the temperature was maintained at 12 • C. Furthermore, Smith et al. [157] showed that outbreaks caused by LMBV in largemouth bass were most prevalent during seasons of high water temperatures, in line with Grant et al. [158], who showed that experimentally infected largemouth bass with LMBV had higher mortality at 30 • C than at 25 • C. Similarly, ISKNV in Chinese perch (S. chuatsi) caused high mortality at temperatures above 25 • C and ISKN only occurred at temperatures above 20 • C [159]. Altogether, these studies showed that an increase in mortality due to iridovirus infections is associated with seasons of high temperatures. ...
Aquaculture has expanded to become the fastest growing food-producing sector in the world. However, its expansion has come under threat due to an increase in diseases caused by pathogens such as iridoviruses commonly found in aquatic environments used for fish farming. Of the seven members belonging to the family Iridoviridae, the three genera causing diseases in fish comprise ranaviruses, lymphocystiviruses and megalocytiviruses. These three genera are serious impediments to the expansion of global aquaculture because of their tropism for a wide range of farmed-fish species in which they cause high mortality. As economic losses caused by these iridoviruses in aquaculture continue to rise, the urgent need for effective control strategies increases. As a consequence, these viruses have attracted a lot of research interest in recent years. The functional role of some of the genes that form the structure of iridoviruses has not been elucidated. There is a lack of information on the predisposing factors leading to iridovirus infections in fish, an absence of information on the risk factors leading to disease outbreaks, and a lack of data on the chemical and physical properties of iridoviruses needed for the implementation of biosecurity control measures. Thus, the synopsis put forth herein provides an update of knowledge gathered from studies carried out so far aimed at addressing the aforesaid informational gaps. In summary, this review provides an update on the etiology of different iridoviruses infecting finfish and epidemiological factors leading to the occurrence of disease outbreaks. In addition, the review provides an update on the cell lines developed for virus isolation and culture, the diagnostic tools used for virus detection and characterization, the current advances in vaccine development and the use of biosecurity in the control of iridoviruses in aquaculture. Overall, we envision that the information put forth in this review will contribute to developing effective control strategies against iridovirus infections in aquaculture.
... However, fish kills, skin lesions, reproductive endocrine disruption and population declines in this region have raised concerns of management agencies and the public. These concerns led to fish health monitoring directed at determining risk factors associated with morbidity and mortality events and identified numerous pathogens and parasites (Blazer et al., 2010;Smith et al., 2015;Walsh et al., 2018) suggesting immunomodulation. Widespread signs of endocrine disruption, including intersex or testicular oocytes (TO) and plasma vitellogenin in male bass (Blazer et al., 2007;Iwanowicz et al., 2009;Blazer et al., 2012;Blazer et al., 2014) ☆ This paper has been recommended for acceptance by Michael Bank. ...
Total mercury (THg) was measured in muscle (fillet) and liver tissue of adult smallmouth bass Micropterus dolomieu collected at multiple sites in the Potomac and Susquehanna River drainages within the Chesapeake Bay watershed. Smallmouth bass in these drainages have experienced episodic mortality events, a high prevalence of skin lesions and reproductive endocrine disruption (intersex or testicular oocytes and plasma vitellogenin in males). A multi-level assessment of general and reproductive health including indicators at the organismal, organ, cellular and molecular levels was conducted on adult smallmouth bass during the spring (prespawn) season. Concentrations of THg were correlated with increased visible abnormalities, increased macrophage aggregates and tissue parasite burdens. In male bass positive correlations of THg were observed with plasma vitellogenin and hepatic transcript abundance of estrogen receptor β1 and androgen receptor α, while there was a negative association with estrogen receptors α and β2 and androgen receptors β. In female bass there was a negative correlation between THg and plasma vitellogenin as well as hepatic transcript abundance of vitellogenin, choriogenin, estrogen receptor β2 and 17β hydroxysteroid dehydrogenase. Associations of THg concentrations with various biological indicators suggest mercury may be an important environmental stressor contributing to the observed adverse effects in smallmouth bass populations.
... Adult male SMB have been documented expressing the egg precursor protein vitellogenin and having testicular oocytes, both markers of intersex due to endocrine disruption. Increased rates of chronic mortality and co-infections of bacterial, viral, and/or parasitic pathogens within both adult and young-of-year (YOY) fish may be indicative of immunosuppression (Smith et al., 2015;Starliper et al., 2013;Walsh et al., 2018). SMB, an indicator species, are extremely sensitive to environmental changes, and previous analyses of water, sediment, and fish tissues have identified the presence of varying levels of environmental contaminants capable of inducing endocrine disruption and immunosuppression Kolpin et al., 2013;McClure et al., 2020;Walsh et al., 2018). ...
Smallmouth bass in the Susquehanna River Basin, Chesapeake Bay Watershed, USA, have been exhibiting clinical signs of disease and reproductive endocrine disruption (e.g., intersex, male plasma vitellogenin) for over fifteen years. Previous histological and targeted chemical analyses have identified infectious agents and pollutants in fish tissues including organic contaminants, mercury, and perfluorinated compounds, but a common causative link for the observed signs of disease across this widespread area has not been determined. This study examines 146 young-of-year smallmouth bass collected from 14 sampling sites in the Susquehanna River Basin, Pennsylvania, USA with varying levels of disease prevalence. Whole fish were extracted by a recently developed modification to the quick, easy, cheap, effective, rugged, and safe extraction method and analyzed by comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry. A targeted analysis was conducted to identify the presence and quantity of 127 known contaminants, including polychlorinated biphenyls, brominated diphenyl ethers, organochlorinated pesticides, and pharmaceutical and personal care products. A non-targeted analysis was conducted on the same data set to identify analytes of interest not included on routine target compound lists. Chromatographic alignment through Statistical Compare (ChromaTOF GC) was followed by Fisher ratio and principal component analysis to reduce the data set from thousands of peaks per sample to a final data set of 65 analytes of interest. Comparisons of these 65 compounds between Normal (no observed health anomalies) and Lesioned (observed health anomaly at time of collection) fish revealed increased levels of three chemical families in Lesioned fish including esters, ketones, and nitrogen containing compounds.
... Within the Chesapeake Bay watershed, adult smallmouth bass have experienced disease and mortality events [8] and signs of reproductive endocrine disruption such as testicular oocytes and vitellogenin in males [9][10][11]. Lesions and mortalities of young-ofyear smallmouth bass [12,13] are also observed. These disease issues are associated with a variety of pathogens including multiple bacterial, viral and parasitic species [8,[13][14][15], suggesting immunomodulation may be occurring. ...
Smallmouth bass Micropterus dolomieu is an economically important sportfish and within the Chesapeake Bay watershed has experienced a high prevalence of external lesions, infectious disease, mortality events, reproductive endocrine disruption and population declines. To date, no clear or consistent associations with contaminants measured in fish tissue or surface water have been found. Therefore, plasma samples from two sites in the Potomac River and two in the Susquehanna River drainage basins, differing in land-use characteristics, were utilized to determine if perfluoroalkyl substances were present. Four compounds, perfluorooctane sulphonic acid (PFOS), perfluoroundecanoic acid (PFUnA), perfluorodecanoic acid (PFDA) and perfluorododecanoic acid (PFDoA), were detected in every fish. Two additional compounds, perfluorooctane sulphonamide (PFOSA) and perfluorononanoic acid (PFNA), were less commonly detected at lower concentrations, depending on the site. Concentrations of PFOS (up to 574 ng/mL) were the highest detected and varied significantly among sites. No seasonal differences (spring versus fall) in plasma concentrations were observed. Concentrations of PFOS were not significantly different between the sexes. However, PFUnA and PFDoA concentrations were higher in males than females. Both agricultural and developed land-use appeared to be associated with exposure. Further research is needed to determine if these compounds could be affecting the health of smallmouth bass and identify sources.
... They are also a top predator and can have significant effects on their prey populations and on habitat complexity and trophic structure (Jackson 2002). Population declines in portions of the Susquehanna river watershed associated with disease (coinfections of multiple bacteria, myxozoan and trematode parasites, largemouth bass virus) in young-of-year smallmouth bass (Arway & Smith 2013, Smith et al. 2015, Walsh et al. 2018) and mortality events, visible skin lesions and similar coinfections of adults in the Potomac watershed (Blazer et al. 2010) have raised concern among the fishing public and resource managers. In addition to these mortality events, visible skin lesions, including melanistic lesions, are commonly observed. ...
Hyperpigmented melanistic skin lesions (HPMLs) of smallmouth bass Micropterus dolomieu are observed in the Potomac and Susquehanna rivers, Chesapeake Bay watershed, USA. Routine, nonlethal population surveys were conducted at 8 sites on the mainstem Susquehanna River and 9 on the Juniata River, a tributary of the Susquehanna River, between 2012 and 2018, and the prevalence of HPMLs was documented. A total of 4078 smallmouth bass were collected from the mainstem Susquehanna River and 6478 from the Juniata River. Lesions were primarily seen in bass greater than 200 mm, and prevalence in the Susquehanna River (8%) was higher (p < 0.001) than in the Juniata River (2%). As part of ongoing fish health monitoring projects, smallmouth bass were collected at additional sites, primarily tributaries of the Susquehanna (n = 758) and Potomac (n = 545) rivers between 2013 and 2018. Prevalence in the Susquehanna River (13%) was higher (p < 0.001) than the Potomac (3%). Microscopically, HPMLs were characterized by an increased number of melanocytes in the epidermis or within the dermis and epidermis. RNAseq analyses of normal and melanistic skin identified 3 unique sequences in HPMLs. Two were unidentified and the third was a viral helicase (E1). Transcript abundance in 16 normal skin samples and 16 HPMLs showed upregulation of genes associated with melanogenesis and cell proliferation in HPMLs. The E1 transcript was detected in 12 of the 16 melanistic areas but in no samples from normal skin. Further research will be necessary to identify the putative new virus and determine its role in melanocyte proliferation.
... Smallmouth bass (Micropterus dolomieu) are an economically important sportfish throughout their native range as well as within areas of the Chesapeake Bay where they were introduced in the 1800s [1,2]. Skin lesions and mortality of adult and young-of-year smallmouth bass have occurred throughout the Potomac and Susquehanna Rivers (Chesapeake Bay watershed, USA), raising concerns of the public and management agencies about both the fishery and ecosystem health of these watersheds [3][4][5]. Co-infections of bacterial, viral, as well as parasitic infections have been associated with these events [4,6,7] suggesting immunosuppression. Estrogenic endocrine disruption as evidenced by testicular oocytes (intersex), vitellogenin in male fish [8][9][10] and the occurrence of contaminants linked to intersex [4,7,11,12] has been confirmed within the areas of the Chesapeake watershed where disease events occur. ...
Smallmouth bass (Micropterus dolomieu) are used as an indicator species in environmental monitoring and assessment studies. However, laboratory-based studies for methods development and effector assessment are limited for this species. Nutrition, a known modulator of teleost physiological responses including immune function, is a critical knowledge-gap sometimes overlooked in the design of laboratory studies. We report the results from a study evaluating a commercially available artificial pelleted diet for bass and live feed (fathead minnows). Following a six-month diet-acclimation period, age-0 smallmouth bass were assessed using morphometric measures, histologic and immune-function end points using conventional methods, miniaturized cell isolation and assay methods as well as imaging flow cytometry. Fish on the two diets did not significantly differ in length, weight, or condition factor, indicating that growth was similar in the two groups. Histologic examination revealed relatively higher levels of macrophage aggregates and accumulation of ceroid/lipofuscin in the spleen as well as hepatocyte changes in the pellet-fed group. Leukocytes from the pellet-fed group exhibited significantly elevated bactericidal activity and significantly depressed mitogen response compared to fish fed live feed. Following exposure to a known inducer of inflammatory responses, bacterial lipopolysaccharide, responses including the transition of leukocytes to an apoptotic/necrotic condition differed significantly based on diet. Histologic findings were consistent with the occurrence of diet-related oxidative stress in the pellet-fed fish. Oxidative stress can be induced by multiple factors including environmental pollutants. For a diet to be useful in laboratory-based studies, it cannot elicit response that could also be induced by experimental treatments. To do so greatly complicates the detection of experimental effects. Until an artificial diet is developed for smallmouth bass that does not produce potentially confounding conditions for laboratory-based studies, use of a live feed appears to be the best option.
... In general, the prevalence and severity of TO were lower than what has been reported in bass from agriculturally impacted sites, where it is not uncommon to have 80-100% prevalence (Iwanowicz et al. 2009;Blazer et al. 2012Blazer et al. , 2014d. These areas have also experienced bass mortality and population declines (Blazer et al. 2010;Smith et al. 2015). To our knowledge, effects such as these have not been noted at AOCs. ...
Adverse effects resulting from potential exposure of wild fishes to estrogenic endocrine disruptors were assessed at seven United States Great Lakes Areas of Concern using biomarkers ranging from organismal (gonadosomatic indices) to tissue/plasma (histology, plasma vitellogenin) and molecular (hepatic gene transcripts) levels. Biomonitoring was conducted on pelagic, top predator species, largemouth Micropterus salmoides and smallmouth M. dolomieu bass and benthic, omnivorous white sucker Catostomus commersonii. Seasonal (spring and fall) comparisons were conducted at select sites. Intersex (testicular oocytes), plasma vitellogenin, and hepatic vitellogenin transcripts were commonly observed in bass species. Testicular oocyte severity was positively, although weakly, correlated with plasma vitellogenin, hepatic transcripts of vitellogenin, estrogen receptor α, and estrogen receptor β2, while negatively correlated with androgen receptor β and phosphoenolpyruvate carboxykinase. No testicular oocytes were observed in white sucker; however, plasma vitellogenin and hepatic vitellogenin transcripts were commonly detected in the males. The results demonstrate the importance of utilizing multiple endpoints to assess exposure to estrogenic compounds as well as the importance of choosing sensitive species.
A murine monoclonal antibody (mAb, IgG2a) was produced for the detection of smallmouth bass (Micropterus dolomieu) immunoglobulin (IgM). The antibody is specific for IgM heavy chain and was shown to also recognize the Ig heavy chain of largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) using Western Blot analysis of plasma from 5 teleost taxa. When applied to the analysis of smallmouth bass total plasma IgM using ELISA, the mAb was found to be effective when used in an inhibition kinetic assay.
Ecological risk assessments play an important role in environmental management and decision-making. Although empirical measurements of the effects of habitat changes and chemical exposure are often made at molecular and individual levels, environmental decision-making often requires the quantification of management-relevant, population-level outcomes. In this study, we generalized a modeling framework to evaluate population-level ecological risk of environmental stress and bioactive chemicals. The modeling framework includes (1) a biological model module that incorporates complex and interacting biological and ecological processes, and environmental stochasticity, (2) an effect module that links the impacts of environmental changes and chemical exposure to individual characteristics, and (3) a population module that makes decisions on the choice of population-level properties to best capture the effects and thus to track in the model based on the target species and the research and management interest. This framework is a 3-module procedure that provides an alternative way for researchers to organize, present and communicate the risk assessment modeling studies. To demonstrate this framework, we used a socioeconomically important riverine fish species, smallmouth bass Micropterus dolomieu, as the model species. We developed an individual-based model as the biological model module. We evaluated the impacts of changing water temperature and flow regimes, and the impacts of exposure to estrogenic endocrine disrupting compounds (EEDC) on smallmouth bass populations in the Chesapeake Bay Watershed, USA. Warm summer water temperatures and year-round high flows had the most severe impacts on the smallmouth bass population. An increase in exposure level to EEDC, both year-round and in summer months, substantially reduced population size, spawner and recruit abundance, and the proportion of quality-length individuals. Acute exposure to EEDC was more detrimental to the population than chronic exposure. Acute exposure during spawning season had the most severe impacts. This modeling framework can be extended to other species, environmental factors and chemicals, and can be used to inform management and conservation decisions.
The influences of eight water temperature and three discharge variables on the time and duration of spawning by smallmouth bass Micropterus dolomieui were evaluated in three main- stem sections and two tributaries of the New River in Virginia and West Virginia. Stepwise discriminant analysis was used to assess the relative importance of each variable in distinguishing between days when spawning did and did not occur. Spawning occurred from late April through mid-July at mean daily water temperatures ranging from 12.5 to 23.5°C. Frequency distributions of spawning dates were nearly identical among study sites, as was the timing of hydrologic events. Spawning activities were interrupted by flooding in June and resumed when water levels were receding. Mean daily water temperature explained most of the variation among groups of daily stream conditions related to spawning activities. Discriminant functions developed from three temperature variables and one discharge variable correctly classified 72% of the days on which spawning did and did not occur. The functions should be useful in predicting smallmouth bass spawning times in other streams.
Shoal Bass Micropterus cataractae is a black bass species endemic to limited sections within the Apalachicola, Chattahoochee, and Flint River systems in Alabama, Florida, and Georgia. The restricted range of this species has resulted in a paucity of life history information, especially regarding reproductive ecology and nesting habitat requirements. The objectives of this study were to describe and document Shoal Bass nesting, associated habitat, and nest-specific environmental variables in the Chipola River, Florida, a tributary of the Apalachicola River. Through the use of radiotelemetry and visual observation, 89 nests were located and used to quantify macrohabitat selection or use. Shoal Bass nesting was documented from mid-April to mid-May during 2011 and 2012. Average nest depth was 102 cm (SE = 3.2), and the average water temperature was 22.6°C (SE = 0.2). Available macrohabitat for the Chipola River was quantified using side-scan sonar and classified into four substrate types: bedrock, boulder, rocky fine, and sand-gravel. More than 80% of all nests were in either boulder (17% availability) or rocky fine (27% availability) macrohabitats. Determining Shoal Bass nesting habitats and associated parameters will provide managers with the knowledge needed for future habitat protection and enhancement in the Chipola River, Florida.
Four of the black bass Micropterus spp. have relatively small ranges: Guadalupe bass M. treculi is found only in Texas and is endemic to portions of the Brazos, Colorado, Guadalupe, and San Antonio rivers. It has been introduced into the Nueces River system; redeye bass M. coosae is endemic to the Tombigbee and Alabama rivers of Alabama and Georgia, the Chattahoochee, Altamaha, and Savannah rivers in Georgia, North Carolina, and South Carolina, and the Coosa River in Tennessee; shoal bass M. cataractae is native to the Apalachicola and Chipola rivers in Florida, the Chattahoochee River in Alabama and Georgia, and the Flint River in Georgia; and Suwannee bass M. notius occurs in the Suwannee and Ochlockonee river systems of Florida and Georgia, and the St. Marks and Wacissa rivers in Florida. Habitat degradation remains the greatest threat to the group, although interspecific introductions are also contributing to the decline of at least one species. Guadalupe bass, adapted for small stream environments, has been affected by stream flow declines, habitat degradation, and genetic introgression. Redeye bass, which prefers small, cool, headwater streams, rarely inhabits the impoundments in its native systems. Shoal bass, inhabiting small, fast-flowing streams, has been eliminated from most of the Chattahoochee River in Alabama due to impoundments, and from some Florida habitats, due to pollution and siltation. Suwannee bass has the most restricted range and is commonly associated with waters influenced by springs.
Fishes were collected at 16 sites within the three major river drainages (Delaware, Susquehanna, and Ohio) of Pennsylvania. Three species were evaluated for biomarkers of estrogenic/antiandrogenic exposure, including plasma vitellogenin and testicular oocytes in male fishes. Smallmouth bass Micropterus dolomieu, white sucker Catostomus commersonii, and redhorse sucker Moxostoma species were collected in the summer, a period of low flow and low reproductive activity. Smallmouth bass were the only species in which testicular oocytes were observed; however, measurable concentrations of plasma vitellogenin were found in male bass and white sucker. The percentage of male bass with testicular oocytes ranged from 10 to 100 %, with the highest prevalence and severity in bass collected in the Susquehanna drainage. The percentage of males with plasma vitellogenin ranged from 0 to 100 % in both bass and sucker. Biological findings were compared with chemical analyses of discrete water samples collected at the time of fish collections. Estrone concentrations correlated with testicular oocytes prevalence and severity and with the percentage of male bass with vitellogenin. No correlations were noted with the percentage of male sucker with vitellogenin and water chemical concentrations. The prevalence and severity of testicular oocytes in bass also correlated with the percent of agricultural land use in the watershed above a site. Two sites within the Susquehanna drainage and one in the Delaware were immediately downstream of wastewater treatment plants to compare results with upstream fish. The percentage of male bass with testicular oocytes was not consistently higher downstream; however, severity did tend to increase downstream.
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Using critical thermal maximum (CTMax) tests, we examined the relationship between upper temperature tolerances and fish size (fry–adult or subadult lengths) of rainbow trout Oncorhynchus mykiss (41–200-mm TL), Apache trout O. gilae apache (40–220-mm TL), largemouth bass Micropterus salmoides (72–266-mm TL), Nile tilapia Oreochromis niloticus (35–206-mm TL), channel catfish Ictalurus punctatus (62–264 mm-TL), and Rio Grande cutthroat trout O. clarkii virginalis (36–181-mm TL). Rainbow trout and Apache trout were acclimated at 18°C, Rio Grande cutthroat trout were acclimated at 14°C, and Nile tilapia, largemouth bass, and channel catfish were acclimated at 25°C, all for 14 d. Critical thermal maximum temperatures were estimated and data were analyzed using simple linear regression. There was no significant relationship (P > 0.05) between thermal tolerance and length for Nile tilapia (P = 0.33), channel catfish (P = 0.55), rainbow trout (P = 0.76), or largemouth bass (P = 0.93) for the length ranges we tested. There was a significant negative relationship between thermal tolerance and length for Rio Grande cutthroat trout (R2 = 0.412, P R2 = 0.1374, P = 0.028); however, the difference was less than 1°C across all lengths of Apache trout tested and about 1.3°C across all lengths of Rio Grande cutthroat trout tested. Because there was either no or at most a slight relationship between upper thermal tolerance and size, management and research decisions based on upper thermal tolerance should be similar for the range of sizes within each species we tested. However, the different sizes we tested only encompassed life stages ranging from fry to adult/subadult, so thermal tolerance of eggs, alevins, and larger adults should also be considered before making management decisions affecting an entire species.Received October 3, 2011; accepted May 12, 2012
We examined the influences of habitat, temperature, stream discharge, and the timing of spawning on the nesting success of smallmouth bass Micropterus dolomieu. Smallmouth bass began spawning when temperatures reached 15°C, and high flow disrupted spawning five times. Larger males spawned earlier than smaller males; a log-linear relation between male length and degree-days accumulated was significant (r = –0.63, P < 0.01). In all, 45 of 105 nests (43%) and 42 of 81 males (52%) produced free-swimming larvae. Production of free-swimming larvae was variable and lower than previously reported, ranging from 98 to 1,802 (mean, 608). Large males (>305 mm total length) accounted for the highest production of free-swimming larvae and also made the most renesting attempts, which suggests that large males can have a strong influence on year-class strength. Stepwise discriminant analysis distinguished successful nests from unsuccessful nests by higher flow at time of nest construction, higher mean temperatures, lower mean stream discharge during nest incubation, and shorter distance to shore. High flow (>10 m/s) was responsible for most nest failures (85%). Increased water velocity at nest sites with increased stream discharge was the most likely cause of nest failures. The increase of mean velocity with increased stream discharge was significantly lower for successful nests than for unsuccessful nests, which showed that nest location determines the degree of exposure to high flows. The temporal pattern of streamflow fluctuation appears to be the most important abiotic factor determining nesting success or failure for smallmouth bass in this perennial stream.
Temperature is an environmental variable thought to influence the susceptibility of fish to infectious diseases. This study demonstrated that juvenile largemouth bass Micropterus salmoides that were experimentally infected with largemouth bass virus (LMBV; family Iridoviridae) experienced greater mortality at 30°C than at 25°C. Juvenile largemouth bass were exposed to equal doses of LMBV and held at three temperatures: 25, 30, and 35°C. Fish held at 30°C suffered mortality at a higher rate than fish held at 25°C and had higher viral loads (viral genomes per gram of tissue) at the time of death. The LMBV-injected fish held at 35°C suffered mortality at rates equal to those of sham-injected controls, suggesting that stressful manipulation at temperatures approaching the upper lethal limit can induce mortality in fish independently of viral infection. These results suggest that temperature is an important determinant of host survival and viral replication in the LMBV system.
We investigated the macrohabitat use, microhabitat use, and food habits of shoal bass Micropterus cataractae and largemouth bass M. salmoides in the upper Chipola River, Florida. We electrofished two macrohabitats (pools and shoals) during the summer (May–August) and fall (September–December) of 1999 and 2000. The ratio of shoal bass to largemouth bass differed among macrohabitats, being highest in the shoals and lowest in the pools. Age-0 and adult (age-1 and older) shoal bass were collected in areas of higher-than-average percentages of rocky substrate in both shoals and pools. Age-0 and adult largemouth bass were associated with areas of reduced current velocity and those with higher-than-average amounts of woody debris. Though the diets of age-0 and adult shoal bass and largemouth bass were similar, a few differences were apparent. Age-0 largemouth bass diets contained grass shrimp Palaemonetes spp., whereas age-0 shoal bass diets contained mostly mayflies (order Ephemeroptera: families Baetidae and Isonychidae). Crayfish and fish were the primary food resources of adult shoal bass and adult largemouth bass, and crayfish became more prevalent than fish in larger individuals of both species. Largemouth bass transitioned to a crayfish-dominated diet at a smaller size than did shoal bass. Considering that we found substantial differences in the habitat associations of these species but relatively few diet differences, habitat partitioning may be important for the coexistence of shoal bass and largemouth bass in rivers and streams. Future shoal bass conservation efforts should focus on maintaining a diversity of habitats where these species coexist and on protecting relatively rare shoals.
Anthropogenic changes in temperature and stream flow, associated with watershed land use and climate change, are critical influences on the distribution and abundance of riverine fishes. To project the effects of changing land use and climate, we modeled a smallmouth bass (Micropterus dolomieu) population in a midwestern USA, large river- floodplain ecosystem under historical (1915-1925), present (1977-1990), and future (2060, influenced by climate change) temperature and flow regimes. The age-structured model included parameters for temperature and river discharge during critical seasonal periods, fish population dynamics, and fishing harvest. Model relationships were developed from empirical field data collected over a 13-yr period. Sensitivity analyses indicated that discharge during the spawning/rearing period had a greater effect on adult density and fishing yield than did spawning/rearing temperature or winter discharge. Simulations for 100 years projected a 139% greater mean fish density under a historical flow regime (64.9 fish/ha) than that estimated for the present (27.1 fish/ha) with a sustainable fishing harvest under both flow regimes. Simulations under future climate-change-induced temperature and flow regimes with present land use projected a 69% decrease in mean fish density (8.5 fish/ha) from present and an unstable population that went extinct during 56% of the simulations. However, when simulated under a future climate-altered temperature and flow regime with historical land use, the population increased by 66% (45.0 fish/ha) from present and sustained a harvest. Our findings suggest that land-use changes may be a greater detriment to riverine fishes than projected climate change and that the combined effects of both factors may lead to local species extinction. However, the negative effects of increased temperature and precipitation associated with future global warming could be mitigated by river channel, floodplain, and watershed restoration.
In an effort to aid in the conservation of black basses, the relative abundance, growth, and mortality of Suwannee bass Micropterus notius and largemouth bass M. salmoides were estimated from four Florida rivers. Fish were collected by electrofishing in the four rivers during 2001 and 2002. Electrofishing catch per unit effort of Suwannee bass was highest in the Wacissa River (95.1 fish/h), intermediate in the Santa Fe River (22.6 fish/h), and lowest in the Withlacoochee (5 fish/h) and Ochlockonee rivers (1.9 fish/h). Catch per unit effort for largemouth bass was also highest in the Wacissa River (50 fish/h), intermediate in the Santa Fe (19.8 fish/h) and Ochlockonee rivers (17.1 fish/h), and lowest in the Withlacoochee River (9.9 fish/h). Mean total length (TL) at age across the four Suwannee bass populations was described by von Bertalanffy growth curves as TL = 386.1 · (1 − e ) for females and as TL = 324.1 · (1 − e ) for males. Mean TL at age across the three largemouth bass populations was also described by von Bertalanffy growth curves as TL = 644.2 · (1 − e ) for females and TL = 427.8 · (1 − e ) for males. Suwannee bass exhibited sex-specific growth rates similar to those of largemouth bass, females experiencing more rapid growth and attaining larger sizes than males (F1, 564 = 20.39; P < 0.01). Suwannee bass total annual mortality (A) averaged 40%, ranging from 28% to 46%. Similarly, largemouth bass total A averaged 40%, ranging from 35% to 46%. The current Florida minimum length limit on Suwannee bass directs fishing mortality almost solely to females, but estimates of fishing mortality are needed to determine whether this is a concern for black bass with a small native range.
Anthropogenic factors have contributed to the precipitous decline of wild Pacific salmon stocks, although the mechanisms and processes at work are largely unknown. Pollution may be one of these factors. Sediments in estuaries are known to act as repositories for contaminants, and estuaries are important habitats for ocean- and river-migrating salmon. We have shown that juvenile salmon Oncorhynchus spp. and their prey bioaccumulate chlorinated hydrocarbons and aromatic hydrocarbons—important classes of toxic xenobiotics. Furthermore, we have shown that exposure to these pollutants can lead to immunosuppression and increased disease susceptibility in juvenile salmon. Whether pollution influences natural disease outbreaks in host populations, including salmon, is currently unknown. It is postulated that the occurrence of disease depends on the interaction of the host, the environment, and the pathogen. Absence of pathogens would reduce the potential for adverse environments to influence disease outbreaks. However, a recent reconnaissance survey of juvenile chinook salmon Oncorhynchus tshawytscha from Oregon coastal rivers revealed that pathogens were an integral component in all systems studied, although the prevalence of the pathogens varied. Furthermore, recent studies of natural fish populations have demonstrated that infectious-disease-induced mortality can significantly reduce the size of the host population. By creating adverse environments (e.g., polluted estuaries) which alter the susceptibility of the host to pathogens that are integral and ubiquitous components of the habitat, pollution increases the probability of disease-related impacts on fish populations.
Largemouth bass virus (LMBV; family Iridoviridae) has recently emerged as a causative agent in fish kills of largemouth bass Micropterus salmoides. Little is known about how the virus is transmitted or what factors predispose fish to mortality subsequent to infection. Concern has nevertheless arisen that activities related to recreational angling may affect transmission dynamics and may alter the susceptibility of infected fish to clinical disease. This study examined the separate effects of two angling-related factors on the susceptibility of juvenile largemouth bass to mortality from LMBV infection and on the transmission of LMBV from infected to uninfected fish. The first factor was hook-and-line angling. Infected fish that underwent a simulated angling treatment did not experience higher mortality or have higher viral loads in their tissues than those that were not angled. The second factor was direct contact between infected and uninfected fish, as would occur in live wells and holding tanks. The LMBV was transmitted from infected to uninfected fish through water, even when direct contact was prevented. Transmission of LMBV between infected and uninfected fish separated by a fenestrated barrier was nearly as efficient as LMBV transmission between infected and uninfected fish that were allowed direct contact. These results imply that angling itself may have only minimal effects on the survival of largemouth bass infected with LMBV but that angling-related practices that place infected and uninfected fish together in a limited water volume may facilitate viral transmission. Partitioning or cooling of live wells and holding tanks, as well as limiting their use, could reduce LMBV-associated mortality and viral transmission.
The feeding activity of warm- and coolwater fishes can be severely restricted during the long period of cold temperatures characteristic of winter in temperate zone lakes and rivers. The effect of such restriction is greater for smaller fish. Weight-specific basal metabolism increases as size decreases; however, there is no corresponding increase in energy storage capacity. Thus, smaller fish tend to be less tolerant of starvation conditions because they exhaust their energy stores sooner. Such size dependence of starvation endurance has often been observed in laboratory experiments. In wild populations commonly subject to winter starvation, population viability hinges on the ability of young of year to complete a minimum amount of growth during their first year of life. From south to north, this ability is increasingly restricted as the growing season shortens and the starvation period lengthens. We show that this constraint is sufficient to explain the present locations of the northern distributional limit for yellow perch Perca flavescens in central and western North America, the northern distributional limit for Eurasian perch P. fluviatilis in Eurasia, and the northern distributional limit for smallmouth bass Micropterus dolomieui in central North America. We also forecast how shifts in North American climate may relax this constraint and permit both yellow perch and smallmouth bass to thrive well to the north of their present distributions.
An intensive seven-year removal of adult, juvenile, and young-of-the-year smallmouth bass (Micropterus dolomieu) from a north temperate lake (Little Moose Lake, New York, USA) resulted in an increase in overall population abundance, primarily due to increased abundance of immature individuals. We developed a density-dependent, stage-structured model to examine conditions under which population control through harvest could result in the increase of a targeted species. Parameter values were derived from a 54-year data set collected from another north temperate lake (Lake Opeongo, Ontario, Canada) smallmouth bass population. Sensitivity analyses identified the demographic conditions that could lead to increased abundance in response to harvest. An increase in population abundance with harvest was most likely to occur when either (i) per capita recruitment at low levels of spawner abundance was large, juvenile survivorship was high, and maturation of age-4 and older juveniles was moderately high or (ii) per capita recruitment at low levels of spawner abundance was slightly lower, yet the maturation rate of age-3 juveniles and adult survivorship were high. Our modeling results together with empirical evidence further demonstrate the importance of overcompensation as a substantial factor to consider in efforts to regulate population abundance through harvest.
We developed standard weight (Ws) equations for Suwannee bass Micropterus notius using the traditional regression-line-percentile (RLP) technique and the newer empirical-percentile (EmP) method. Length and weight data for 2,137 Suwannee bass at least 11 cm total length (TL) collected from all 10 populations within the species' narrow geographic range were used to develop the equations. The resulting Ws equations were log10W = −5.548 + 3.303 × log10L and log10W = −1.014 − 0.583 × log10L + 0.828 × (log10L) (where W is weight in grams and L is TL in millimeters) for the RLP and quadratic EmP techniques, respectively. The RLP-derived Ws equation exhibited a small (
The recruitment of smallmouth bass Micropterus dolomieu in rivers commonly exhibits a high degree of annual variation. We examined three rivers in Virginia with the objectives of determining the magnitude of recruitment variability, identifying a functional index for measuring year-class strength, and examining the relationship between stream discharge and recruitment success. Recruitment in the three study rivers varied by as much as an order of magnitude among years. The electrofishing catch per unit effort of age-0 smallmouth bass in September–November was a reliable measure of year-class strength. The recruitment success of smallmouth bass was significantly related to mean June streamflow using a nonlinear model, with the strongest year-classes produced in years with moderate flows. Mean June streamflow reasonably predicted the abundance of age-0 smallmouth bass in the fall. Our data suggest that stream discharge during and immediately after spawning could be critical to smallmouth bass recruitment success.
The Guadalupe bass Micropterus treculii is endemic to Texas and is threatened by introgression with introduced smallmouth bass M. dolomieu as well as habitat degradation. This study described and quantified the movements and habitat associations of Guadalupe bass to assess the factors that may influence current populations. Radio-tagged adult Guadalupe bass were tracked in the Pedernales River (n = 12) and South Llano River (n = 12) from January through August 2008. Available microhabitats were measured and modeled in terms of depth, velocity, substrate, and cover for about 1.5 km in the Pedernales River and 1.2 km in the South Llano River. Rates of movement were greatest during the reproductive season, ranging from less than 1 to 9 m/d. Instream cover (such as undercut banks and woody debris) was preferred during daylight hours throughout the study period, although the distances from cover increased from January to August. Habitat shifts from cover to open water occurred at night and from woody structures to boulders and ledges during a large flood pulse. The habitats most suitable for adult Guadalupe bass had a depth of 1.0 m and a current velocity of 0.05 m/s, and habitat selection was strongest for eddy mesohabitats with smaller substrates. By July, the Guadalupe bass in the South Llano River were associated with runs with greater current velocities, whereas those in the Pedernales River were associated with pools with greater depths, largely owing to the low flows and reduced habitat availability in the Pedernales River. Environmental factors, including the availability and suitability of instream cover, are probably the strongest influences on the distribution and abundance of Guadalupe bass.
The shoal bass Micropterus cataractae has been listed as a species of special conservation concern by the American Fisheries Society and the Alabama Department of Conservation and Natural Resources. We describe seasonal movement, habitat use, and home range of 23 shoal bass fitted with radiotelemetry transmitters in Little Uchee Creek, Alabama. During this tracking period, the region experienced a drought that probably influenced shoal bass habitat choice and movement during reduced streamflow. During most of the year, shoal bass preferred runs and eddies, low current velocity (≤0.30 m/s), moderate depth (0.4–0.8 m), and boulder and bedrock substrates. Most shoal bass in Little Uchee Creek had a strong affinity for shoal habitat. Generally, movement was minimal (1.2 m deep) that contained sand bottom and had a water velocity of zero. However, 87% of the radio-tagged shoal bass did not emigrate from the shoal habitat as it became dewatered; these fish subsequently perished. Small home ranges and the lack of movement by many shoal bass from the dewatered shoal habitat to deepwater pool refuges warrant concern to ensure that adequate water quantity is maintained in streams where these fish are found.
Introductions of nonnative smallmouth bass Micropterus dolomieu into central Texas streams resulted in introgressive hybridization with an endemic allopatric congener, the Guadalupe bass M. treculii. The objectives of this study were to use the variation at 14 microsatellite DNA loci to examine the frequencies of Guadalupe bass, smallmouth bass, and their hybrids 10 years after supplemental stockings of Guadalupe bass in the Blanco River. Genetic analysis identified 40% of individuals as smallmouth bass, 51% as smallmouth bass × Guadalupe bass hybrids, and 9% as other Micropterus hybrids. Pure Guadalupe bass were not collected. Despite supplemental stocking, the frequency of pure Guadalupe bass appears to have declined in the Blanco River in the past 10 years. These results emphasize the need for a current survey of the genetic status of the species throughout its native range.
The influences of eight water temperature and three discharge variables on the time and duration of spawning by smallmouth bass Micropterus dolomieui were evaluated in three mainstem sections and two tributaries of the New River in Virginia and West Virginia. Stepwise discriminant analysis was used to assess the relative importance of each variable in distinguishing between days when spawning did and did not occur. Spawning occurred from late April through mid-July at mean daily water temperatures ranging from 12.5 to 23.5°C. Frequency distributions of spawning dates were nearly identical among study sites, as was the timing of hydrologic events. Spawning activities were interrupted by flooding in June and resumed when water levels were receding. Mean daily water temperature explained most of the variation among groups of daily stream conditions related to spawning activities. Discriminant functions developed from three temperature variables and one discharge variable correctly classified 72% of the days on which spawning did and did not occur. The functions should be useful in predicting smallmouth bass spawning times in other streams.
We documented the nesting chronology, nest site selection and nest success of smallmouth bass Micropterus dolomieu in an upstream (4th order) and downstream (5th order) reach of Baron Fork Creek, Oklahoma. Males started nesting in mid-Apr. when water temperatures increased to 16.9 C upstream, and in late-Apr. when temperatures increased to 16.2 C downstream. Streamflows were low (77% upstream to 82% downstream of mean Apr. streamflow, and 12 and 18% of mean Jun. streamflow; 47 and 55 y of record), and decreased throughout the spawning period. Larger males nested first upstream, as has been observed in other populations, but not downstream. Upstream, progeny in 62 of 153 nests developed to swim-up stage. Downstream, progeny in 31 of 73 nests developed to swim-up. Nesting densities upstream (147/km) and downstream (100/km) were both higher than any densities previously reported. Males selected nest sites with intermediate water depths, low water velocity and near cover, behavior that is typical of smallmouth bass. Documented nest failures resulted from human disturbance, angling, and longear sunfish predation. Logistic exposure models showed that water velocity at the nest was negatively related and length of the guarding male was positively related to nest success upstream. Male length and number of degree days were both positively related to nest success downstream. Our results, and those of other studies, suggest that biological factors account for most nest failures during benign (stable, low flow) streamflow conditions, whereas nest failures attributed to substrate mobility or nest abandonment dominate when harsh streamflow conditions (spring floods) coincide with the spawning season.
Pylodictis olivaris (flathead catfish) is a large, obligate carnivore native to drainages of the central United States that has been introduced widely beyond its native range. We report on the introduction of flathead catfish into the Delaware and Susquehanna River drainages, which represents the northernmost occurrences among Atlantic drainages. In the Delaware Basin, flathead catfish have been found in the Schuylkill River and the mainstem of the Delaware River. Recent sampling activities in the Schuylkill River suggest successful reproduction and establishment of a viable population there. In the Susquehanna basin, the fish has been found in the lower and central portion of the river mainstem. As in the Delaware Basin, recent sampling indicates that reproduction is occurring in the Susquehanna River. The introduction of this species has the potential to adversely affect ongoing anadromous fish restoration programs and native fish conservation efforts in the Delaware and Susquehanna basins. A cooperative effort will be required to mitigate the effects of this introduction.
Environmental stressors can predispose fish to mortality from infectious disease. This study examined the effects of two factors, water quality and physical crowding, on the responses of fish to viral infection. Juvenile largemouth bass Micropterus salmoides were experimentally inoculated with largemouth bass virus (LMBV), an emerging pathogen in the family Iridoviridae. In separate experiments, fish were exposed to various concentrations of nitrate (0, 40, 200, and 400 mg/L) and were housed at either high or low population densities. Survival time, viral load (quantity of virus in tissues), and body condition were measured as outcomes. Nitrate, as well as other water quality parameters such as ammonia, nitrite, and pH, affected mortality rates and viral loads in complex ways. Paradoxically, increased nitrate concentrations were associated with reduced mortality rates in juveniles exposed to LMBV. In general, rapid fluctuations in the concentrations of dissolved toxins had greater impact on sensitivity to viral infection than did persistently high levels of these toxins. Fish housed at high density experienced increased mortality rates, elevated viral loads, and reduced body condition compared with fish held at low density. These results demonstrate that both physiochemical and social environmental stressors can affect the survival and condition of largemouth bass infected with LMBV.
Predicting the effects of climate and global warming on fisheries necessitates understanding the effects of temperature on fish. For more than two decades, index gill netting in the Ontario and New York waters of eastern Lake Ontario has provided catch statistics and age data to assess the population dynamics of smallmouth bass, an important warm-water sport species. The relationship between log year-class strength and July-August water temperatures was positively correlated and highly significant, explaining 34 to 48 percent of the variance. From 1973 to 1996 the strongest year-classes came from the El Niño years of 1973, 1983, 1987-1988, and 1995, with some weak year-classes in the La Niña years, 1985, 1989, and 1976, and the weakest from the cool 1992 to 1993 period, which were associated with the Mount Pinatubo eruption. Proportional year-class strength and survival rate (67% for ages less than 4 and 62% for ages 4-10) were used to assess relative abundance of the fishable stock (ages 4-10). Relative abundance of older fish was greatest in the mid- to late 1980s, approximately 4-fold higher than when it was weakest, from 1996 to 1998. The strong 1995 and 1994 year-classes initiated a resurgence of older fish in 1999. Relative abundance from 2001 to 2003 was projected to be very close to average and threefold higher than during the lowest period. A 1°C increase in global warming will increase year-class strength almost 2.5-fold and a 2°C increase 6-fold. Although many factors, including cormorant predation, affect smallmouth bass in eastern Lake Ontario, temperature and year-class strength substantially influenced recent fluctuations in abundance, and the relationship now exists to remove the effects of temperature on recruitment dynamics.
We reviewed the published and gray literature associated with Neosho Smallmouth
Bass Micropterus dolomieu velox and the genetically distinct Ouachita lineage. Substantial
interstream variation appears to occur among these populations, particularly related
to age. The Neosho subspecies is more abundant, grows faster, and lives longer than the genetically
distinct Ouachita lineage. Recruitment is highly variable among streams for both
populations and appears to be related to some undescribed aspects of hydrology but also likely
reflect bias due to sampling gear. Information on annual and seasonal trends is lacking for the
Neosho subspecies and the Ouachita lineages, particularly as related to the spawning period.
Conservation efforts for these lineages might benefit from agencies partnering to achieve goals
that extend beyond a particular agency’s responsibilities and state boundaries. Recognition
of spatial and temporal considerations, combined with a better understanding of the population
dynamics as related to abundance, growth, mortality and reproduction, would benefit the
creation of more effective conservation and management strategies for genetically distinct
populations of Smallmouth Bass M. dolomieu.
This second edition of the book Fish Diseases and Disorders, Viral, Bacterial and Fungal Infections volume 3 represents a major update on the viral, bacterial and oomycete disorders of finfish and shellfish. Since publication of the first edition (in 1999), considerable advances have been made and therefore all the chapters have been thoroughly revised. The new and more eloquent research and current techniques have extended our knowledge and understanding of these infectious organisms. Researchers from Europe, North America, Australia and Asia have been involved in updating this book. With the addition of new information, some of the older texts in the original chapters have been condensed; this is to ensure a more focused and comprehensive reviews. For this edition, deletion and/or combination a couple of the original chapters, have been made and added three new chapters (Chapter 6 on 'Alphaviruses', Chapter 7 on 'Oncogenic Viruses' and Chapter 21 on 'Genomics of Finfish and Shellfish Microbial Pathogens'), which have been written by new authors. There are 22 new authors who have offered to write new chapters and/or update many of the original chapters. The aims, philosophy, focus, audience and format of this second edition have remained unchanged, and the authors hoped that this edition will continue to be useful to colleagues.
(1) Nesting asynchrony among male smallmoth bass, Micropterus dolomieui Lacepede, varied significantly from year to year (1980-85). Much of the observed variation in timing of nesting was explained by a consistent relationship between the size of individual males and their thermal history (number of degree-days above 10 degrees C) immediately prior to nesting: larger males accumulated fewer degree-days prior to nesting than smaller males. Larger females also appeared to spawn earlier than smaller females. (2) Environmental effects were stronger than phenotypic effects in explaining the seasonal timing of reproduction in males that renested in subsequent years. A significant proportion of adult males did not nest, and the magnitude of that proportion was negatively density-dependent. Nesting habitat was not limiting the number of nesters. (3) Removal experiments showed that the territorial behaviour of nesting males did not affect the seasonal timing of nesting among males of different sizes nor did it limit the total number of nesting males. These experiments did show that removal of experienced spawners from nesting areas in one year was followed by increased recruitment of inexperienced males to the nesting areas in subsequent years. However, this was not accompanied by a significant increase in the total number of nesters. (4) Two bioenergetic hypotheses can account for why male body size acts as a constraint on the timing of reproduction: (i) large males emerge from winter with a lower energy deficit and are therefore capable of breeding before smaller males: (ii) large males allocate energy to reproduction rather than growth earlier in a season than small males. Both of these hypotheses could also account for our observation of size dependence in female reproductive behaviour.
Mortalities of young-of-the-year smallmouth bass were observed in the Susquehanna River basin in the summers of 2005, 2007, and 2008. Although relations among water-quality, streamflow, and fish mortality in the Susquehanna are poorly understood, elevated water temperature and low dissolved oxygen are suspected stressors, especially during times critical for development of smallmouth bass (May 1-July 31).
In 2008-09, environmental conditions in nursery microhabitats (microhabitats) and main-channel habitats were compared by measuring dissolved-oxygen concentration and water temperature twice hourly. During critical months of 2008, daily minimum dissolved-oxygen concentration was significantly lower in microhabitats than the nearby main channel; dissolved oxygen in microhabitats fell below the national criterion of 5.0 mg/L on 20-30% of days in the critical months. Dissolved-oxygen concentration in 2008 was 1-2 mg/L less than 2009 for both habitats owing to streamflows twice those of 2008. Water temperatures were warmer in 2008 and in both years were closely correlated with sun exposure rather than habitat type.
Data from 2008-09 indicate microhabitats are more stressful than the main channel. Comparing dissolved-oxygen and water-temperature data from the Susquehanna River to data from the Delaware or Allegheny Rivers indicates fish in the Susquehanna are most likely to experience stress from these factors.
This study examined how spring-flow (SF) contributions to streams related to the distribution and abundance of smallmouth bass Micropterus dolomieu in a predominately pasture landscape in Missouri, USA. Stream segments (N = 13) with similar landscape characters were classified by SF volume into high SF (HSF) or low SF (LSF) groups. The densities of smallmouth bass, channel unit (CU) use and temperature-selection patterns were assessed for several life stages and frequency distributions for age 0 fish. More smallmouth bass were present in stream segments with HSF influence. Age 0 fish were twice as likely to be present in HSF stream segments. Older age classes were present in stream reaches independent of SF contribution. For all age classes, the use of particular CUs did not depend on SF influence. All age classes were more likely to be present in pools than other CUs. Microhabitat temperature selection differed among age classes. Age 0 fish selected warmer temperatures with a gradual shift towards cooler temperatures for older age classes. The length frequency of age 0 fish was skewed towards larger individuals in streams with limited SF influence, whereas the length frequency in HSF stream segments was skewed towards smaller individuals. The benefits of significant groundwater via SF influence seem to be related to increased hatch or survival of age 0 fish and the availability of optimal temperatures for adult smallmouth bass growth. Thermal refugia and stable flows provided by springs should be recognised for their biological potential to provide suitable habitat as climate change and other land-use alterations increase temperature regimes and alter flow patterns. Published in 2011 by John Wiley & Sons, Ltd.
The long-term effects (November 1977-October 1978) of elevated temperature on smallmouth bass, Micropterus dolomieui (age 0+ at stocking) were evaluated in outdoor channels located on the Tennessee River in Alabama, the southern limit of the native range of this species. Temperature treatments, with three channels per treatment, were at the ambient regime of the Tennessee River and 3, 6, and 9 C above ambient. Actual temperatures ranged from 1 to 30 C in the ambient channels and from 10 to 38 C in the +9 C channels. Under extreme summer conditions there was a 10% (by volume) refuge zone of 35 C water in the +9 C channels. Mean annual survival rates ranged from 84% in the +3 C regime to 92% in the +6 C regime; survival was 87% in both the ambient and +9 C treatments. Substantial growth occurred throughout the range 20 to 32 C. After 322 days, net biomasses of smallmouth bass in the four thermal regimes were not significantly different (range, 85–105 kg/hectare). Reproduction at age I occurred in all four regimes. The broad thermal requirements for growth and survival of smallmouth bass in this study were characteristic of warmwater species. To protect smallmouth bass from elevated temperature, the following numerical temperature criteria were derived: (1) a mean weekly average temperature of 32–33 C in the mixed water body would permit satisfactory growth; and (2) a maximum temperature of 35 C for short-term exposure during the summer growth period would avoid potential lethal effects.
Population densities of smallmouth bass Micropterus dolomieu (SMB) have declined in streams of the Missouri Ozark border region since the 1940s while replacement by largemouth bass M. salmoides (LMB) has occurred in some cases. A recent field study found that two habitat variables, known to have been influenced by human activities, largely explained present densities of SMB and LMB throughout streams in this region. Densities of SMB declined with increasing maximum summer temperature (range, 23–33°C) and percent pool area while LMB densities increased with these variables. To explore these correlations from a bioenergetics perspective, we determined maximum consumption rates of SMB and LMB at 18, 22, 26, and 30°C. Consistent with the field study's findings about temperature, maximum consumption results indicated that SMB scope for growth becomes progressively restricted at temperatures higher than 22°C, whereas this does not occur until 26°C for LMB. Maximum consumption rates of SMB also averaged twice those of the LMB, indicating a much greater per capita demand for prey biomass by SMB and suggesting SMB have a lesser capacity to tolerate prey base decline than LMB. The higher consumptive demand by the SMB may relate to the field study's finding that SMB density declined with increasing pool area. Increases in pool quantity are accompanied by reduced food production and the loss of prey types known to be of importance to SMB. Findings indicate that changes in growth conditions for SMB and LMB may be a proximate cause for shifts in distribution of black bass Micropterus spp. in Ozark border region streams.
Introductions of black basses Micropterus spp. beyond their native ranges have led to hybridization within the genus. In the southeastern USA, the potential for hybridization appears high because species introductions have been common in reservoirs. We determined the extent of hybridization between smallmouth bass M. dolomieu and spotted bass M. punctulatus in reservoirs in which introductions of either species into the native range of the other species had occurred. Three allozyme loci were used to distinguish the two species and their hybrids. Significant hybridization occurred in two of three reservoirs where introductions had been reported. In Lake Chatuge, Georgia–North Carolina, where the Alabama subspecies of spotted bass M. p. henshalli was introduced, 77 of 276 fish had hybrid genotypes, and only 2 fish had genotypes of the native smallmouth bass. In Thurlow Reservoir, Alabama, where smallmouth bass were introduced and Alabama spotted bass were native, 3 of 17 fish had hybrid genotypes. Only I fish with a possible hybrid genotype was identified in two reservoirs containing native smallmouth bass and northern spotted bass M. p. punctulatus.
Allele-frequency differences at 11 polymorphic protein loci provided discrete genetic markers with which to estimate the extent of hybridization among native and introduced centrarchid basses in central Texas streams. Native Guadalupe bass Micropterus treculi and northern largemouth bass M. salmoides salmoides now coexist with introduced Florida largemouth bass M. s. floridanus and smallmouth bass M. dolomieui in these streams. Interspecific hybridization was detected in three of four populations from the Blanco and San Marcos rivers, hybrids making up at least 31.8% of the individuals sampled. Complex hybridization patterns were evident, because F1, F2, and backcross hybrids were detected. At least one individual exhibited genetic markers of largemouth, smallmouth, and Guadalupe bass. Extensive multispecies hybridization threatens the survival of the endemic Guadalupe bass.
We defined relationships between current velocity and displacement of young smallmouth bass Micropterus dolomieui from nests, and between velocity and the distribution, swimming, respiration, feeding, and growth of larger young. Young that had recently risen from the nest gravel (7–9 mm standard length, SL) were displaced from field nest sites and from laboratory flumes at low velocities (8 mm/s). Nests in areas of higher velocities (15 mm/s) failed to produce young. Comparison of respiration and foraging rates of young fish (16–71 mm SL) in laboratory flumes suggested that the ratio of feeding reward to energy expenditure reached a maximum at current velocities between 80 and 130 mm/s. This velocity range produced maximum growth in the flumes and was also the range most frequented by young (43–116 mm SL) in the Mississippi River.
Over 92,000 marked fingerling smallmouth bass were stocked in Big Piney River, 1952-1955. An estimated 63,600 smallmouth bass were caught between 1953, when the first stocked fish entered the creel, and 1958 when no more marked fish were caught. Of that number, not more than 2,100 were stocked fish. This is a little more than 3% of all the bass caught and a little more than 2% return of stocked fish.
We used fish population and food consumption data from five Ohio impoundments plus results from computer simulations to (1) examine sources of sampling error in estimating Proportional Stock Density (PSD), an index of fish population structure, (2) evaluate the relative effects of growth, mortality, and recruitment on PSD, and (3) assess use of PSD to predict outcomes of predator-prey interactions when the largemouth bass (Micropterus salmoides) is the major piscivore in medium to large impoundments (>50 hectares) with complex fish communities. When largemouth bass were collected with electrofishing gear, estimates of PSD varied considerably. During the spring, PSD was positively related to water temperature. PSD was lowest during summer when large bass were not vulnerable to electrofishing gear and increased in autumn when water temperatures declined. The PSD of a largemouth bass population in one impoundment ranged from 11 to 36% over a 4-year period as growth, exploitation, natural mortality, and recruitment changed. We used a computer simulation model to show that PSD increased linearly with survival and curvilinearly with growth. Random variations in recruitment caused large fluctuations in PSD and we concluded that, in medium to large impoundments, recruitment was likely to have more influence on PSD than either growth or survival. We also examined the effectiveness of largemouth bass as predators in Ohio impoundments and the likelihood of observing changes in the PSD of prey populations in response to changes in size structure of largemouth bass populations. In only one of five impoundments were bluegills (Lepomis macrochirus) and crappies (Pomoxis spp.) a major part of largemouth bass diets. When present, the gizzard shad (Dorosoma cepedianum) was the major prey. We used a bioenergetics model to estimate annual food consumption by a dense population of largemouth bass. Largemouth bass could consume most of the gizzard shad production in years when shad produced small year classes; however, largemouth bass would not control bluegill or crappie populations when gizzard shad were present.
Increased angling effort on black bass (Micropterus dolomieui and Micropterus salmoides) requires more efficient and effective management to maintain the quality of the resource. Baseline data needed to develop effective management policies were collected for largemouth bass and smallmouth bass in 19 lakes and 1 river in Maine, representing 19,000 hectares of water. A card requesting only information on bass was distributed to anglers at bass club fishing tournaments and to the general public at sporting shops, general stores, and fishing lodges. Fishing diaries were given to selected anglers who had received specific instructions. Data were analyzed by the Proportional Stock Density index (PSD), a measure of population size structure. Populations of largemouth bass in eight waters had significant PSD values greater than 60%, indicating too few small fish. In three lakes, PSD was between 40 and 60%, indicating balanced populations. Populations of smallmouth bass in eight waters had significant PSD values greater than 60%, also indicating too few small fish. PSD was less than 40% in two waters, indicating too few large fish. Smallmouth bass in the one river had a PSD between 40 and 60%, suggesting balanced numbers. Regulation changes of increased size limits to increase sizes of predators are recommended for three of eight waters that were analyzed in detail. A slot limit protecting intermediate-size fish is recommended for the river.
To enhance headwater stream fisheries, nonindigenous redeye bass Micropterus coosae were introduced into 16 north-central Tennessee streams from the mid 1950s through the early 1960s. Reassessment occurred from June 1994 to October 1995 by sampling 18.6 km of stream channel in 31 streams by backpack electrofishing. Meristic criteria identified redeye bass in 11 streams within three river drainages and hybrids (redeye bass X smallmouth bass M. dolomieu) in 20% of the Micropterus spp. sampled in 6 streams within two river drainages. Based upon electrophoretic criteria, hybrid genotypes were identified in 66% of the Micropterus spp. collected from 9 of 31 streams sampled. Introgression is highly probable in the Ocoee, Obed, and Roaring river systems. These hybridizing populations illustrate the consequences of introducing nonindigenous redeye bass into streams containing indigenous smallmouth bass.
The Potomac River basin is an area where a high prevalence of abnormalities such as testicular oocytes (TO), skin lesions, and mortality has been observed in smallmouth bass (SMB, Micropterus dolomieu). Previous research documented a variety of chemicals in regional streams, implicating chemical exposure as one plausible explanation for these biological effects. Six stream sites in the Potomac basin (and one out-of-basin reference site) were sampled to provide an assessment of chemicals in these streams. Potential early life-stage exposure to chemicals detected was assessed by collecting samples in and around SMB nesting areas. Target chemicals included those known to be associated with important agricultural and municipal wastewater sources in the Potomac basin. The prevalence and severity of TO in SMB were also measured to determine potential relations between chemistry and biological effects.
We conducted an allozyme survey of genetic variation at 33 gene loci in smallmouth bass Micropterus dolomieu from 57 localities encompassing most of the range of the species, but with an emphasis (51 samples) on the Interior Highlands (Ozark and Ouachita uplands). Samples exhibited a moderate amount of total genic diversity (HT = 0.068), but high genetic heterogenity (FST = 0.383). Phylogenetic analyses supported recognition of three clades from the Interior Highlands: (1) the previously recognized Neosho smallmouth bass in Ozark tributaries of the middle Arkansas River; (2) the Ouachita smallmouth bass in the Little and Ouachita river drainages of the Ouachita Highlands; and (3) a clade that included populations from the White, Black, Missouri, and other streams in the northern and eastern Ozarks. This third clade was very similar to populations from the Ohio and upper Mississippi river basins, and, on the basis of allele frequency parsimony, more closely related to them than to the Neosho and Ouachita smallmouth basses. To preserve genetic diversity and the options that divergent native stocks represent for future management, stock transfers of smallmouth bass should take into account potential effects on native forms of the species.
A length-categorization system was developed to assess structure of fish stocks with greater precision than is possible using Proportional Stock Density (PSD). Three new size categories - preferred, memorable, and trophy - were developed to accompany previously established stock and quality lengths. Like minimum stock and quality lengths, minimum lengths for the new categories are defined as percentage lengths of the all-tackle, world-record fish. Length ranges from or near which minimum stock, quality, preferred, memorable, and trophy lengths should be selected were computed for all freshwater fish species having a world-record length listed by the International Game Fish Association in 1982. Minimum lengths corresponding to each of the five size categories are proposed for several species. By arraying samples of fish population data or angler catch data according to the five size-group categories, a length-frequency distribution can be easily assessed and verbalized. Relative Stock Density (RSD) or models for catch rates also can be developed to set management objectives that are easily understandable, yet reflect recruitment, mortality, and growth functions of fish populations and communities. Desirable percentages and catch rates for size-group categories may differ among individual waters or geographic regions depending upon management objectives and the capacity to produce the species of interest.
The disciplines of fish immunology and endocrinology have periodically met at a cross-road. This interdisciplinary overlap is perhaps most evident in the case of stress physiology. Such research has clearly demonstrated intersystem communication in which ligands traditionally associated with the endocrine system affect target cells of the immune system. However other ligands of the endocrine system, namely estrogens, are also known to exert actions on cells of the immune system. In the instance of fish immunology, documentation of such intersystem communication is scarce. Given the recognition of estrogenic endocrine disrupting chemicals in the environment and the increased application of immune status as an indicator of wild fish health, it is essential that mechanistic and physiological effects of estrogen on immune function are elucidated in fish. The following chapter is a general review of the effects of steroid hormones on immune function. The effects of estrogens on immune function in mammals and fish are specifically emphasized, and the possible significance of estrogenic endocrine disrupting chemicals is also considered.
Smallmouth bass larvae became highly sensitive to oxygen deficiency on the second day after hatching and continued so to the 10th day. During this period they could not survive exposure to 1 mg O2 l–1 for 3 h at 20° C, and many were killed within 1 h. At 2 mg O2 l–1 half the larvae survived 3 h at 20° C; at 2.5 mg l–1 most survived, and at 3.5 mg l–1 all survived. Resistance to oxygen deficiency was regained by the 11th day, the majority of the larvae withstanding a 3-h exposure at 1 mg O2 l–1. At 25° C the effects of low oxygen concentration were intensified. At 3 and 4 mg O2 l–1 and 20° C the normally quiescent larvae became very active, even swimming to the surface 5 or 6 cm above the substrate. Increasing the temperature increased this response. Smallmouth larvae were more sensitive than large-mouth bass larvae to oxygen deficiency.
A number of chemicals present in the environment have been shown to mimic or antagonize the actions of steroid hormones, an issue often described as "endocrine disruption/modulation". There is very little evidence, however, to support the hypothesis that exposure to endocrine-disrupting chemicals is a global environmental health problem. In this paper, we demonstrate a high incidence of intersexuality in wild populations of riverine fish (roach; Rutilus rutilus) throughout the United Kingdom. These reproductive disturbances are consistent with exposure to hormonally active substances and are associated with discharges from sewage treatment works that are known to contain estrogenic chemicals. This is the first documented example of a widespread sexual disruption in wild populations of any vertebrate and indicates that reproductive and developmental effects do result from exposure to ambient levels of chemicals present in typical British rivers.