Journal of Applied Ichthyology

This study estimated the length–weight relationships (LWRs) and length–length relationships (LLRs) for 6 fish species in the middle Yangtze River basin and its adjacent lakes (Ochetobius elongatus (Kner 1867), Rhinogobio cylindricus (Günther 1888), Hemibagrus macropterus (Bleeker 1870), Pseudobagrus albomarginatus (Rendahl 1928), Siniperca knerii (Garman 1912), and Coreosiniperca roulei (Wu 1930)). All fish specimens were seasonally collected through scientific research monitoring of fishery resources from May 2020 to June 2023. A triple gillnet (with a mesh size of 20–30 mm, a height of 2.0–4.0 m, and a length of 30–50 m) was employed for the capture. The LWRs and LLRs of all specimens were highly significant (p<0.05), featuring high correlation coefficients (r2 ≥ 0.9511). These findings not only enriched the data in FishBase but also offered supplementary references for the management of the Yangtze River during its fishing ban period.

Relationships between weights (W, dry weight [DW] and wet weight [WW] and lengths L, standard length [SL], head length [HL], and caudal peduncle depth [CD]) and these between DW and WW were examined in 61 freshwater fishes using formula W = aLb and DW = aWWb, respectively. The parameters of the SL–DW, SL–WW, HL–DW, HL–WW, CD–DW, CD–WW, and WW–DW relationships were determined for 60, 61, 57, 58, 50, 50, and 61 taxa, respectively, with the criterion where the estimated R-square was greater than 0.8. For the genus or higher taxonomic level, parameters of the SL–DW and SL–WW relationships were determined for 20 taxonomic groups with the same criterion to each species. For the three eel-like species, the SL–DW and SL–WW relationships were largely consistent with the pooled taxonomic data. In contrast, noneel-like species exhibited variations in these relationships across species. Systematic variations in the SL–DW and SL–WW relationships were observed at the order and family levels, except in Salmonidae, Cobitidae, and Cottidae. However, at the genus level, these relationships were generally consistent among species. These intragroup variations should be considered when applying these equations to ecological and taxonomic studies.

Studying size frequency, size relationships, and the conditions of fish is vital for managing the resources properly. Some biological aspects of the fishes in Geray Reservoir were studied from October 2017 to August 2018. Fish were sampled monthly by overnight setting of gillnets. Fishers’ catch was also used. Fish were dissected and sexed. Biological parameters were measured following standard procedures. Four fish species ( Oreochromis niloticus , Tilapia rendalli , Carassius auratus , and Cyprinus carpio ) belonging to the Cichlidae and Cyprinidae families were identified. From the total 570 fish specimens collected, 426 (74.7%), 66 (11.6%), 44 (7.7%), and 34 (6.0%) were O. niloticus , T. rendalli , C. auratus , and C. carpio , respectively. In Geray Reservoir, most of the sampled fish specimens were found in length intervals of 24–27, 18–24, 24–32, and 41–49 cm for O. niloticus , T. rendalli , C. auratus , and C. carpio , respectively. Length–weight relationships of O. niloticus , T. rendalli , C. auratus , and C. carpio were curvilinear and statistically significant ( p < 0.05). For all introduced fish species, b values were less than 3, negative allometry growth. The mean Fulton condition factor of O. niloticus , T. rendalli , C. auratus , and C. carpio was > 1 and showed significant variation ( p > 0.05) among months. In Geray Reservoir, all four economically important fish species are fully established and contribute significantly to local livelihoods. However, in this sampling scheme, the number of catches of T. rendalli , C. auratus , and C. carpio deserve due attention for the management of the exotic fish species. The data presented in this work could be vital for further biological investigations, helping researchers to assess the status of the introduced fishes in the reservoir and for local fish managers to select appropriate management strategies.

The Denkoro River is the largest river in Borena Sayint National Park (BSNP) of Ethiopia. Many studies have been conducted on the terrestrial biodiversity of the park. However, there are no baseline data on the fish biodiversity of the park. Therefore, this study aimed to assess the diversity, determine the biology of the dominant fishes, and compile baseline data. Fish specimens were collected using gillnets (4, 6, 8, 10, and 12 cm stretched mesh sizes), monofilaments (5, 10, 15, and 20 mm mesh size), and hook and lines. Fish samples in the Denkoro River were collected in wet (September) and dry (December) seasons, 2022. A total of 398 fish specimens were collected from three sites in both seasons. Five fish species, Labeobarbus intermedius, Garra dembecha, Clarias gariepinus, Labeobarbus beso, and Oreochromis niloticus, were identified from the river. The diversities (H′) of fish species in the Wachau, Buke, and Kernemariam sites in the dry season were 1.45, 0.95, and 0.64, respectively. During the wet season, fish species diversity was lower than that in the dry season, with Shannon diversity indices of 1.33, 1.18, and 0.93 at the Wachau, Buke, and Kernemariam sites, respectively. L. intermedius was the most abundant species, with 42.9% of the total catch. The length–weight relationships of L. intermedius and L. beso followed a curvilinear pattern, described by the equations TW = 0.005TL3.12 and TW = 0.01TL2.94, respectively. In all sites, females were more numerous than males and statistically significant (Chi-square, p < 0.05). For sustainable fish conservation and development, further research on fishing activities, feeding habits, and fish biology is needed. Important management measures such as regulated fishing activities, habitat restoration, and spawning ground protection should be performed in the area.

The rainbow trout, Oncorhynchus mykiss, is the most extensively cultured coldwater fish species in India. However, skeletal deformities remain a significant concern and are frequently reported in rainbow trout farming operations. The incidence of skeletal deformities can serve as an indicator of the quality of rearing conditions and environmental factors. The present study was conducted to assess the skeletal deformities of rainbow trout, from selected farms in Himachal Pradesh, and Uttarakhand, India. During the study, physicochemical parameters such as water temperature, pH, dissolved oxygen (DO), nitrogen and phosphorus compounds, and chlorides were recorded. The brain, gill, and muscle tissues were examined under optical microscope to inspect myxozoan parasite infections. Nevertheless, myxozoan parasites were not detected in the microscopic examination. For histopathological analysis, tissue samples from the internal organs were processed. The degree of acinar cell necrosis, fibrosis, and macrophage aggregation were determined through histopathological examination. The skeletal deformities, whirling behavior, and mortality were directly associated with the major pancreatic anomalies but no signs of parasite presence.

Identification of polymorphism in growth‐related genes and their association with growth traits is an area of intense research. The growth rate is the most sought‐after economic trait in the breeding program of fish. The significant association of polymorphism will aid in marker‐assisted selection and speed up the genetic improvement program. The present study was performed in a population of common carp belonging to an ongoing selective breeding program at ICAR‐CIFE, Rohtak Center. A total of 50 common carp based on the breeding value for body weight were selected and bifurcated into two groups: high and low performers. Each fish had three records (based on pond age) for growth‐related traits, viz., body weight ( Bw ), body length ( Bl ), and body height ( Bh ). At 200 days of pond age, the mean Bw, Bl , and Bh for high performers was 494.28 ± 52.12 g, 23.764 ± 0.63 cm, and 9.36 ± 0.35 cm, respectively, whereas the mean Bw , Bl , and Bh for low performers was found to be 165.72 ± 17.31 g, 16.20 ± 0.57 cm, and 6.40 ± 0.23 cm, respectively. The DNA was extracted from the fin clips of these fish. Five primers were used to amplify five distinct regions of the growth hormone gene covering five exons and four introns. The positive PCR products were purified and subjected to Sanger sequencing. The sequences with a Phred quality score above 20 were imported in Sequencher V for SNP hunting. Five polymorphic sites were detected, viz., C165 (amplicon 3), D60 (amplicon 4), D114 (amplicon 4), E90 (amplicon 5), and E185 loci (amplicon 5). The population genetic analysis was performed using GenAlex V. The D60 and E185 loci significantly deviated from the Hardy–Weinberg equilibrium ( p < 0.05). Growth association was performed for the polymorphic loci using a linear model by invoking PROC GLM in SAS. The loci C165, D60, and E90 were significantly associated with the Bw , Bl , and Bh . The results obtained in this study must be utilized in the ongoing selective breeding of common carp to speed up genetic improvement.

To reconstruct the life history of Coilia nasus in the Shandong section of the Yellow River, an electron probe microanalyzer (EPMA) was employed to analyze the Sr and Ca values in the otoliths of 12 individuals collected from Pangkou Bay. The results indicated that the life history of C. nasus is complex and diverse, the individuals in this study can be categorized into five distinct patterns. Pattern I includes P1, P2, P3, and P4, whose life history tracks indicate hatching in brackish water near the Yellow River estuary; after approximately 1 year, they begin to migrate along the Yellow River to Pangkou Bay for spawning. Pattern II encompasses P9, P12, and P13, which hatch in freshwater habitats; as these individuals grow, there is an abrupt change from Stage 1 to Stage 2, but their life history does not extend to marine habitats with high Sr/Ca values, and after about 1 year, they migrate along the Yellow River to Pangkou Bay for spawning. Pattern III includes P6, P8 and P10, which also hatch in freshwater habitats and experience abrupt changes; however, the mapping analysis reveals a large area of red and yellow concentric rings, indicating a history of seawater habitat and an extension of their life history to Laizhou Bay. Pattern IV is represented by P11, whose living environment was relatively stable, with no significant abrupt changes and no migratory life history characteristic, which presumed to be a freshwater settlement type that passively entered the Yellow River due to the flood season of Dongping Lake. Pattern V is exemplified by P7, whose analysis results show two trips to freshwater and brackish water habitats, both of which produced significant pattern changes which indicates that it conducted a reproductive migration at the first instar, swam to the Yellow River estuary after spawning, and migrated to Pangkou during the reproductive period of the following year to lay eggs until it was captured. This study demonstrates that most individuals in Pangkou Bay are of the migratory type. Compared with the sexual maturity of individuals in other waters of the Yangtze River basin, Pangkou Bay is identified as an important spawning ground for the migratory type of C. nasus .

Global climate change significantly influences environmental temperature, affecting the feeding patterns, growth, and overall health of fish. Understanding how fish respond to thermal changes is crucial, particularly for growth and stress response in aquaculture. This study examines the effects of different acclimation temperatures on the expression of stress, appetite, and growth-related genes in Nile tilapia (Oreochromis niloticus). Quantitative real-time PCR method was employed to analyze the expression of genes for growth hormone (gh) from the pituitary, insulin-like growth factors (igf1 and igf2), ghrelin, and heat shock proteins (hsp70 and hsp90) from the liver of juvenile Nile tilapia acclimated to 31°C (control), 34°C, and 37°C for 14 days. Results revealed that the expression of hsp70 and hsp90 as well as the level of blood glucose were significantly upregulated at 37°C in both males and females, indicating a pronounced stress response due to higher acclimation temperature. Conversely, the expressions of gh, igf1, and igf2 were highest at 34°C, stimulating metabolic processes and promoting somatic growth. In comparison, significantly lower expression of these genes was observed at 37°C, suggesting an inhibitory effect of higher temperatures on growth processes. Expression of ghrelin followed a similar pattern to that of GH and IGFs with higher levels at 34°C correlating with increased appetite and growth, but a decreased expression at 37°C, indicating reduced feeding activity resulting from thermal stress. These findings underscore the critical role of maintaining optimal temperatures in aquaculture settings and provide valuable insights into the physiological mechanisms underlying thermal adaptation in Nile tilapia under varying environmental conditions.

The current study was conducted at the Bangladesh Fisheries Research Institute in Cox’s Bazar, from February 2023 to April 2024. Oyster ( Crassostrea virginica ) growth and survival rate were studied in a recirculating aquaculture system (RAS). The study also evaluated the impact of various water parameters (viz., temperature, pH, dissolved oxygen [DO], salinity, alkalinity, nitrite, nitrate, and ammonia) on oyster development. Oysters were cultivated in T1, T2, and T3 using two replications for each treatment. RAS was used with continuous aeration throughout the two treatments (T1 and T2), while non‐RAS continuous aeration was given during the control treatment (T3). 50, 60, and 55 oysters were presented in three treatments. Three distinct marine microalgae ( Nannochlorum spp., Tetraselmis spp., and Nannochloropsis spp.) were added to tanks for feeding oysters. Statistically significant differences ( p < 0.05) were found in the T1 therapy group, which had the highest specific growth rate per day (0.119%) and survival rate (92.85%), followed by T2 (87.5%) and T3 (77.5%). In addition, first treatment (T1) continuously measured the largest weight (36.08 g), length (6.51 cm), and width (6.43 cm); however, T2 showed a significant depth rate (4.44 cm). Optimum oyster population, salinity (29.5 ppt), pH (7.25), DO (5.12), temperature (30.75°C), and other water quality indicator levels displayed a significant correlation with oyster growth performance for the T1 group rather than T2 and T3. However, the T2 group was also treated under RAS circumstances. The findings demonstrated that RAS can significantly enhance oyster growth and survival‐controlling water indicators, which provide valuable insights for sustainable aquaculture practices in the coastal areas of Bangladesh.

Growth rates are generally obtained from back-calculation of increments of otolith readings and based on the assumption that mean annual growth can be scaled directly to the distance between age rings. Although otoliths continue to grow even when somatic growth ceased. To analyse growth rates of yellow eel, a passive integrated transponder (PIT) mark-recapture study was performed in four water bodies (Delfland, Markiezaatsmeer, Süderpolder and Vinkeveense Plassen) in the Netherlands. PIT-tags were used as an alternative method instead of the generally applied back-calculation of annual increments from otolith readings. During 2017–2020, 2209 eels were tagged individually and in the subsequent years, 541 eels were recaptured. The mean annual growth rate decreased with increasing length of eel, with growth rates of 2.2–8.8 cm/year for undifferentiated (sex undetermined) eel between 30 and 50 cm and 1.3 and 5.7 cm/year for female eel between 50 and 80 cm. Differences in growth rate were also observed between the four water bodies, which having consequences to population demographics, such as age at first maturity.

Water pollution resulting from petroleum derivatives, notably diesel fuel oil, has emerged as a significant environmental concern recently. The experiment was conducted to find out the impact of diesel oil on morphology, behavior, and changes in internal organs i.e., heart, intestine, kidney, and liver in Nile tilapia (Oreochromis niloticus). There were controls and three groups of Nile tilapia (Oreochromis niloticus) exposed to 0 mL/L (control), 0.5 mL/L, 1.0 mL/L, and 1.5 mL/L of diesel for 15 days. Several morphological changes such as a broken fin, rough scale, increased mucous, and discolored gill were recorded. The treated fish displayed erratic swimming patterns, rapid operculum movements, and hovering in the water column, displaying signs of weakness whereas the untreated (control) remained calm and normal. Probit analysis revealed that the mortality rates were increased significantly (p<0.05) with the increase of diesel concentrations. Multiple histopathological abnormalities were found and they were fragmentation of myocardial muscle fiber and formation of degenerative vacuoles in the heart; degeneration of epithelium, submucosa, and hemorrhage in the mucosa of the intestine; hemorrhages of glomerulus and dilation of tissues in the kidney; and enlargement of central vein, degeneration of hepatocyte, dilation of the sinusoid, hemorrhage, vacuolization of hepatocytes, necrosis, and thickening of the hepatocytic cells in the liver. This study also concluded that the dissolved oxygen levels decreased with the increase of oil concentrations, which led to poor water quality and had a significant effect on morphology, behavior, histology, and mortality. This study will grow social awareness and people will handle commercial diesel oil properly during transportation. Thus, the present findings might be helpful to save aquatic animals as well as aquatic environments.

Climate change is causing saline intrusion, negatively affecting aquaculture productivity on a global scale. It is necessary to explore suitable species for coastal aquaculture in water with low to moderate salinity. Thus, the objective of the present study was to assess the impact of salinity on the growth performance, muscle composition, and blood parameters of a farmed fish, Gangetic mystus (Mystus cavasius). For this experiment, the fingerlings were raised in the aquarium for 60 days. Three distinct salinities, specifically 3, 6, and 9 parts per thousand (ppt), were employed for treatment 2 (T2), treatment 3 (T3), and treatment 4 (T4), whereas treatment 1 (T1) was referred to as the control with a salinity of 0 ppt. Increasing salinity did not have any influence on the water quality parameters. The survival rates were 97.5 ± 0%, 96.25 ± 1.25%, 92.5 ± 2.5%, and 90 ± 5% for T1, T2, T3, and T4, respectively. The highest specific growth rate (SGR) and the percentage of weight gain (PWG) and the lowest food conversion ratio (FCR) were recorded at T1. T2 and T3 showed descending values for SGR and PWG and ascending values for FCR. Moreover, the body protein percentage reduced by about 2%, and lipids increased by 13% in T3 compared to T1. RBC and Hb exhibited an inverse relation with increasing salinity, whereas WBC and glucose displayed an opposite trend due to stressed conditions. Thus, the study implies that while salinity does hinder growth performance and compromise the immune system to some degree, M. cavasius is capable of enduring salinity levels of up to 6 ppt while maintaining a satisfactory survival rate.

Bosten Lake is an important inland freshwater lake in China, which is rich in fishery resources. However, due to various factors, its fishery resources have declined. The length–weight relationship (LWR) is of great significance for fish research and fishery management. This study was based on the samples of 17 freshwater fish species collected from 10 sampling points in Bosten Lake from March 2023 to November 2024. The LWRs were determined, the regression parameters and the coefficient of determination ( R ² ) were calculated, and the fish condition factor BW/TL ³ was analyzed. The results showed that the b value of the LWR parameters of the 17 freshwater fish species ranged from 1.262 to 3.665. The b values of most fish species were within the expected range. The LWRs of all fish species were significantly different ( p < 0.05), and the R ² values ranged from 0.746 to 0.999. The LWR of Aristichthys nobilis was the strongest, and that of Rhodeus ocellatus was the weakest. This study reported for the first time the LWRs of Channa argus in the lake, and its b value was the highest, and the growth pattern was related to its ecological niche. The research results provide basic data and theoretical basis for fish ecology research, fishery resource management, and lake ecological protection.

Artificial expansion of shipping routes in the course of international trade opens up fish migration routes for numerous species. Since 2006 migration of four different goby species took place from the Ponto–Caspian region to the Lower Rhine. Neogobius fluviatilis , Neogobius melanostomus, Proterorhinus semilunaris and Ponticola kessleri were able to establish in the local fish community of the Lower Rhine. Besides the four other goby species, Knipowitschia caucasica migrated from the Ponto–Caspian region to the Lower Rhine as well in 2019. Due to increasing abundance in the last years and lack of information regarding population dynamics, feeding activity and prey preferences of the dwarf goby, the length of 1218 Caucasian dwarf gobies was analysed as well as the diet of 519 individuals in the course of May 2021 to February 2022. The populations of three different locations along the Lower Rhine were examined in winter on differences in population dynamics and feeding ecology. Analysis of the population over time suggests that K. caucasica in the Lower Rhine is an annual species with spawning during summer. The juvenile individuals of the Caucasian dwarf goby increased in total length until winter, while the adults vanished after spawning. Both juveniles and adults mainly fed on zooplankton and insect larvae. The feeding activity of the dwarf goby was higher in summer than in winter and started to increase as early as February. No difference in winter prey was recorded between populations at different sites, as all populations fed mostly on copepods and chironomids.

Establishing length–weight relationships (LWRs) is essential for conserving fish populations, especially where gaps hinder efforts, particularly crucial for elasmobranch populations in the Gulf of Guinea. This study presents LWRs established for six species of elasmobranchs landed by artisanal maritime fishing in Mayumba, located in the south of Gabon. The data were collected in May 2022 and between September 2022 and March 2023. This work provides the first LWRs for six elasmobranch species that have not yet been referenced at the regional level. One of these species, Paragaleus pectoralis, lacks referenced data on FishBase.

Caohai Lake, hailed as a gem on the Yunnan–Guizhou Plateau, is currently being faced with serious biological invasion threats. Among the most influential invasive species, the Procambarus clarkii (Girard, 1852) is causing various adverse effects on the lake’s ecosystem. However, there has been little attention paid to this issue for a long time. In light of this, this study conducted a sample collection in August 2022 to investigate the total length–weight relationships (LWRs) and condition factors (K) of the target species with the aim of providing fundamental data for the upcoming ecological restoration in Caohai Lake. The results are as follows: (1) P. clarkii was distributed throughout the lake, with females exhibiting larger body sizes than males; (2) the LWRs were expressed as: W♂ = 2 × 10−6 TL3.66 (R2 = 0.90 and n = 227); W♀ = 4 × 10−6 TL3.39 (R2 = 0.95 and n = 259), both showing positive allometric growth pattern and indicating, the weight gain rate of males is significantly faster than that of females during the growth period; (3) the K was 0.27 ± 0.04%, indicating robustness in P. clarkii in the lake. These findings underscore that urgent scientific measures should be taken to handle the rapid invasion of P. clarkii in Caohai Lake.

The population size structure and length–weight relationships (LWRs) are fundamental tools in fishery science, providing valuable insights into the health, dynamics, and management of fish populations and contributing to the sustainable use of aquatic resources. The data used in this study were estimates from the main small pelagic fishes exploited in the Gambia. They were collected using surface and bottom gillnets between November 2020 and October 2021 during scientific fishing operations. The main small pelagic fish size composition showed a modal class of 20 cm for Ethmalosa fimbriata, 21 cm for Sardinella aurita, 22 cm for Sardinella maderensis, and 30 cm for Trachurus trecae. The parameter b value of these fish species ranged from 1.6831 to 2.9461, and the correlation coefficient ranged from 0.81 to 0.95. Statistical LWRs for all species were very significant. Information obtained is essential in reviewing and establishing basic management measures for depleted shared pelagic stocks in the Gambian fisheries and the sub-region. In the context of poor data fisheries, such results also encourage the Gambian government and intergovernmental subregional organizations to support data collection in the long term.

In the present study, the DNA barcoding of the nematode parasite infecting Ompok bimaculatus and Nemacheilus anguilla fish species was carried out in Barvi Reservoir, Maharashtra. To ascertain the taxonomic status of these nematode parasites, an 18S gene marker was used. Accurate identification of fish parasites is essential to formulate preventive strategies and to study host–environment relations. The present study did barcoding of the nematode parasites of the fishes caught from the Barvi Reservoir using the nuclear 18S rDNA (SSU) sequence. The nuclear 18S rDNA (SSU) was amplified into two overlapping amplicons and sequenced to identify the species based on the sequence similarity with the NCBI GenBank database. The present study sequences (both fragments) showed 98% similarity with the species of Eustrongylides. The average genetic distance value between the present study sample and species of Eustrongylides was 0.003. In the phylogenetic tree also, the sequence was clustered with the species of Eustrongylides with significant bootstrap values. The present study identified the nematode parasite of the fish caught from the Barvi Reservoir, as species of Eustrongylides. The species-level identification could not be possible due to the insufficient/lack of reference sequences in the database. It indicates the knowledge gap concerning the species-specific molecular markers for nematode parasites of the fish.

In recent decades, climate change has significantly altered the environmental dynamics of aquatic ecosystems, profoundly impacting the intricate balance of life within them. This review paper delves into the multifaceted impacts of climate change on the physiology of aquatic life, emphasizing temperature and salinity as pivotal ecological factors unique to aquatic environments. The intricate relationship between rising global temperatures and their repercussions on freshwater and seawater habitats forms the cornerstone of this exploration. Elevated temperatures and escalating frequency of extreme heatwave events have reshaped the paradigm for fish survival, pushing them beyond optimal temperature thresholds. Furthermore, the study delves into the interconnection of seemingly disparate abiotic factors, where heightened greenhouse gas concentrations amplify coastal winds, precipitating coastal upwelling. The consequence—nutrient-rich yet oxygen-deprived waters—fuels a cascade of challenges, inducing hypoxic conditions that significantly impact aquatic organisms. The plight of fish, as ectotherms finely tuned to environmental fluctuations, is underscored, illuminating their susceptibility to temperature variations. The direct correlation between external and internal temperatures, exacerbated by climate-induced fluctuations, accentuates the urgency of addressing climate change’s impact on aquatic habitats. This review disentangles the complex web of interconnected environmental shifts, illuminating their far-reaching repercussions on the physiology of aquatic life. It emphasizes the imperative for collective endeavors aimed at understanding and addressing the challenges imposed by our evolving climate on these indispensable ecosystems.

Length-weight relationships are useful for stock assessments and modeling alternative conservation and management strategies for both native and non-native fishes. We developed length-weight relationships for 18 native and non-native riverine fishes in the lower Red River catchment. Fishes were sampled in the summer and autumn seasons between May 2021 and March 2024 via electrofishing and gill nets. Measurements for each specimen consisted of total length (mm) and weight (g). We provide L-W relationships for 14 native fishes consisting of 5 families (Lepisosteidae, Catostomidae, Ictaluridae, Sciaenidae, and Polyodontidae) and 4 non-native species belonging to the family Cyprinidae. We collected 6,845 individuals ranging from 67 alligator gar to 1,848 smallmouth buffalo. All the L-W relationships were significant (p<0.05), and the majority (72% of species) of relationships between length and weight had r2 values > 0.70. Our findings provide insight into the L-W relationships of riverine fishes and can be useful for modeling alternatives targeted at native fishes of recreational value and the removal efforts of non-native fishes.

Invasive carp populations have purported a negative influence on native biota at high densities. These invasive fishes (i.e., bighead carp Hypophthalmichthys nobilis, silver carp Hypophthalmichthys molitrix, grass carp Ctenopharyngodon idella, and black carp Mylopharyngodon piceus) each exhibit similar life history characteristics. In the Neosho River-Grand Lake system (i.e., John Redmond Reservoir, Kansas, downstream to Grand Lake O’ the Cherokees, Oklahoma), only bighead carp and grass carp have been documented to date. The distribution and status of bighead carp throughout this system were previously unknown due to limited historical data and low abundance. While few bighead carp are encountered within this system, grass carp exhibited relatively higher abundance a were used to provide insights into bighead carp. Captures of both species were used to inform management and suppression efforts. Sampling locations (n = 18) were established for environmental DNA analyses throughout the Neosho River-Grand Lake system. We sampled 13 sites using a suite of gears for standardized targeted fish sampling. All invasive carp were measured, sexed, and otoliths removed for ageing and microchemical analysis. Grass carp were processed for ploidy testing following the U.S. Fish and Wildlife Service protocol. Environmental DNA analyses generated positive results for the eDNA presence of bighead carp and silver carp. Otolith age estimates suggest fish are long lived and supported by multiple year classes. Additionally, a sampled two-year-old grass carp demonstrates spawning and recruitment potential. Otolith microchemistry suggests largescale broad movement patterns. Ploidy testing confirmed the first documented evidence of diploid grass carp in the Neosho River-Grand Lake system and revealed reproductive viability. Our results may provide future insights into locations for containment, removal, and/or eradication.

We investigated the gastric evacuation rate (GER) and maintenance ration (MR) for the adult pointhead flounder Cleisthenes pinetorum (77–421 g) at 4°C, 9°C, and 14°C which reflect the bottom, middle, and surface temperatures of their habitat in early summer. GERs were obtained from gravimetric experiments with 34 flounders fed juvenile walleye pollock Gadus chalcogrammus as prey. A 169-day feeding experiment for 67 pointhead flounders fed krill Thysanoessa inermis was undertaken to measure MR. The effects of a 10°C temperature increase (Q10) on the GER and the MR were 6.55 and 2.04, respectively, indicating that the effect of temperature was greater on GER than on MR. As a result, the differences between the GER and MR, indicating the maximum amount of food ingestible for growth, were 2.8 and 30.7 cal·g⁻¹ day⁻¹ at 4 and 14°C, respectively. The water temperature on the sea floor generally remained at <4°C from winter through summer, but exceeded 10°C in the surface layer of Funka Bay, where pointhead flounders were sampled. Therefore, their growth rate should be considerably limited if they remain in the bottom layer. The unique ecology of this species among the flatfishes of floating from sea floor and feeding at pelagic zones may represent a strategy to compensate for the physiological limitation of growth at low temperatures.

To determine sex and maturity stages accurately without any physical injury and stress, especially for sensitive and high-value fish species, employing a noninvasive ultrasound imaging technique could be a desirable approach. The ultrasound imaging method as a powerful eco-friendly tool was established to determine sex, gonad volume, gonadosomatic index (GSI), and reproductive stages in the Indian shad, hilsa (Tenualosa ilisha). About 30 hilsa (15 males and 15 females) of different maturity stages were collected from the river Ganga round the year using gill nets. The ultrasound sonography (USG) was then employed in hilsa to determine the computed GSI. The fresh gonad volume of hilsa was determined using a water displacement method to ascertain actual GSI values. There was no significant difference between the calculated, real, and actual GSIs (P>0.05) in both males and females. The validation of the precise maturity stages of ultrasound images of the gonad by the histological architecture indicated that USG images of the hilsa gonad depicted exact stages of maturity in both sexes except for stages I and II in males. The sex of the fish was accurately ascertained using ovarian ultrasound scanning for all the specimens. The calculated USG-based ovarian volume was positively correlated (R2 = 0.97) with the actual and real ovarian volumes. The noninvasive and reliable ultrasonography technique was found to be an accurate and valid tool to track gender and gonadal development and predict the spawning periodicity in hilsa.

The freshwater bodies of Nepal host a great deal of fish diversity; however, the molecular study of Nepalese fish is still in its early stages. Conservation management tactics require knowledge of the real species composition, often impeded by descriptions of intermittent species based on traditional taxonomy. Catfish, one of the most overfished taxa on the planet, are abundant and heavily exploited in the eastern region of Nepal. Hence, actual catfish diversity in this region needs to be examined using a combined morphological and molecular DNA barcoding approach. In this study, we sequenced the cytochrome oxidase subunit I (COI) gene in Nepalese fish species for the first time and used it for molecular identification. Altogether, 99 specimens representing 29 species belonging to 21 genera and 8 families were successfully barcoded. They were found to be 98.5–100% identical to the known sequences deposited in the GenBank and BOLD databases. Of these, two species, Amblyceps arunachalense and Erethistoides sicula, were recorded for the first time in Nepal. Out of 29 species, one species was found to be Endangered, one species under Vulnerable, two species under Near Threatened, one species under Data Deficient, and 24 species under Least Concern. The intraspecific genetic distances within species ranged from 0 to 5%. The highest intraspecific genetic distances (Kimura 2-parameter) were found among the individuals of two species, namely, E. sicula (4%) and Glyptothorax telchitta (5%), indicating the presence of putative (sub)species. The interspecific genetic distances among the catfishes in eastern Nepal ranged between 8.47% (between Glyptothorax trilineatus and G. cavia) and 26.38% (between Amblyceps arunachalense and Chaca chaca). The GC content at the 1st, 2nd, and 3rd positions of the codons was found to be 42.4%, 49.3%, and 43.8%, respectively. These findings will support future initiatives for fish resource inventory, monitoring, and management. It is also an important input to the DNA barcode library of catfish in the eastern region of Nepal.

The black jewfish (Protonibea diacanthus) occurs in tropical coastal waters throughout the central Indo-Pacific. It has long been valued as an important recreational and artisanal fishery species but has become increasingly targeted by commercial fisheries due to demand for its large swim bladder. To better understand how changes in fishing pressure may impact the sustainable exploitation of P. diacanthus populations throughout Eastern Australia, we evaluated the reproductive biology of the species across two management regions in Central Queensland. Reproductive characteristics studied included the size at maturity, fecundity, spawning mode, and season. Spawning periodicity was evaluated throughout the two major management regions and revealed an increase in the gonadosomatic index during the early austral spring, followed by evidence of spawning occurring from September through March with a peak from September to November. Females were found to produce ∼4.5 million ± 1.4 million oocytes (mean ± SE) per batch. Spawning periodicity did not vary latitudinally but was found to differ from other regions in northern Australia. The present study provides reliable maturity and fecundity information to improve future assessment and sustainable management of P. diacanthus.