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Parasite attractants: Identifying trap baits for parasite management in aquaculture
Abstract
Aquatic parasites may respond to various attractants and cues to find and infect a host. Traps that use these attractants as ‘bait’ have potential to reduce the number of pathogenic agents in aquaculture environments. This study examined four potential attractants (i.e., urea, host mucus, parasite conspecifics and light) and the response of two problematic marine parasite species, to identify the most suitable bait for trap development in finfish aquaculture. Two globally distributed parasite species (i.e., Neobenedenia girellae, (Hargis, 1955); and Cryptocaryon irritans, Brown, 1951) were chosen as models. A chemotaxis experiment was used to compare the attractiveness of each species' infectious life stage to urea, host mucus, parasite conspecifics and a seawater control, while a phototaxis experiment was used to identify phototactic responses of the parasites to light or dark. We found that urea and light attracted more than twice the number of infective protozoans and flukes (monogeneans), respectively, compared to other attractants/controls. Cryptocaryon irritans theronts were positively chemotactic to urea (Beta Regression Analysis; Odds Ratio (OR) 2.69, p = 0.00017), while Neobendenia girellae was positively phototactic to light (Mixed Effect Logistic Regression; OR 2.5, p = 0.0014). A final experiment examined the emergence of C. irritans over a 24-hour period and identified that the vast majority excysted at night (ANOVA; p-value <0.001). In contrast, previous studies have shown that the majority of N. girellae oncomiracidia hatch in the morning. This indicated that the best time to deploy traps to capture infective C. irritans theronts and N. girellae oncomiracidia would be prior to sunset and sunrise, respectively. The manipulation of urea and light and other potential attractants combined with strategic deployment of traps to coincide with the emergence of infectious life stages may prove useful in aquaculture where parasite epidemics can compromise production and animal welfare.
... Such infective stages typically use similar stimuli and behaviours to orient themselves in the water column in a way which increases the likelihood of contact with a susceptible host. Many exhibit positive phototaxis, aggregating near the water surface, where light intensity is highest [27][28][29][30][31][32]. Others, such as myxozoan actinospores or digenean cercariae, may accumulate in the upper layers or the water column simply by being buoyant [33,34]. ...
... Others, such as myxozoan actinospores or digenean cercariae, may accumulate in the upper layers or the water column simply by being buoyant [33,34]. Parasite infective stages may also exhibit chemotaxis, seeking hosts actively through attraction to urea, mucus, or other chemical signatures [32]. Collectively, these characteristics result in a concentration of infective parasitic stages in the upper layers of the water column, where most fish are kept and fed in net pen mariculture. ...
... For net pen operations, an increase in water depth can also prevent parasites originating in the benthos from reaching farmed fish near the surface [54,55]. Understanding the temporal rhythm of parasite egg and larvae production can be used to time deployment of traps designed to capture infective stages [32]. There is also a growing interest in integrated multitrophic mariculture, where the metabolic and feed waste from fish culture serves as feed for the culture of other organisms at lower trophic levels. ...
Marine fish are a nutritious and high-value food commodity, but many wild-capture fisheries are in decline. Thus, marine fish culture is expected to expand greatly in coming years. Management of disease is a major problem in this industry, and metazoan parasites are among the most significant disease agents in terms of economic loss and animal welfare. Current methods for controlling metazoan parasites are mostly reactionary and rely on chemical treatment. Such methods are ultimately unsustainable. Here, we summarise the life cycles of marine metazoan parasites and how this knowledge can be used for nonchemical management and control. To aid the sustainable growth of marine fish culture, we advocate for a renewed research focus on the basic life history characteristics of parasites.
... No acompanhamento sanitário dos cultivos, devese sempre observar o comporta mento dos animais, o consumo alimentar e os principais índices zootécnicos e produtivos. Periodicamente, devese também selecionar uma amostra de indivíduos para uma análise PARASITOS NOS CULTIVOS DE PIRARUCU (Arapaima gigas) mais minuciosa, por meio da dissecação de alguns exemplares (Skilton;Saunders & Hutson, 2020;Clausen et al., 2015). Nesse tipo de análise é importante que se examine com cautela os aspectos externos e internos do animal, como adesão das escamas, quantidade e aspecto do muco, presença de protusões, lesões, abaulamento do abdômen e principalmente a pre sença de ectoparasitas visíveis a olho nu (TavaresDias, 2009;Martins, 2004). ...
... No acompanhamento sanitário dos cultivos, devese sempre observar o comporta mento dos animais, o consumo alimentar e os principais índices zootécnicos e produtivos. Periodicamente, devese também selecionar uma amostra de indivíduos para uma análise PARASITOS NOS CULTIVOS DE PIRARUCU (Arapaima gigas) mais minuciosa, por meio da dissecação de alguns exemplares (Skilton;Saunders & Hutson, 2020;Clausen et al., 2015). Nesse tipo de análise é importante que se examine com cautela os aspectos externos e internos do animal, como adesão das escamas, quantidade e aspecto do muco, presença de protusões, lesões, abaulamento do abdômen e principalmente a pre sença de ectoparasitas visíveis a olho nu (TavaresDias, 2009;Martins, 2004). ...
No Brasil, uma das principais espécies nativas cultivadas é o pirarucu (Arapaima gigas), um peixe que reúne características favoráveis ao cultivo e à comercialização. Entretanto, com a intensificação dos cultivos surgem também as enfermidades, com destaque para as parasitoses. Observando a escassez e dispersão das informações sobre o tema, o presente trabalho se propôs a fazer um compilado das espécies já relatadas em interação de parasitismo com A. gigas e as implicações práticas aos cultivos. Averiguou-se que são conhecidas 38 espécies de parasitos, agrupados em 11 grandes grupos taxonômicos, e esses parasitam principalmente intestino, estômago, pele, brânquias e nadadeiras. O levantamento realizado revela a grande diversidade de parasitos que podem afetar as pisciculturas de pirarucu, reafirmando a necessidade e importância de um acompanhamento sanitário adequado atrelado às boas práticas de manejo, garantindo o bem-estar dos animais e a segurança alimentar do consumidor. Palavas-chave: piscicultura, espécies nativas, sanidade
... mm) (Latidae) were also purchased from an aquaculture supplier (Spring Creek Barramundi farm) in February 2019. For these two experiments, L. calcarifer were used as a positive control, because this species is known to be susceptible to N. girellae and C. irritans under laboratory conditions (Skilton et al., 2020) and is routinely used as a host for in vivo parasite cultures in the Marine Parasitology Laboratory at James Cook University. On arrival, L. dimidiatus were quarantined for 2 weeks in separate tanks (dimensions: 22×14×13 cm L×W×H; 4 l) and in two recirculating systems and monitored for clinical signs of disease. ...
... The marine ciliate protozoan C. irritans has been cultured at James Cook University in the Marine Parasitology Laboratory for previous studies (Vaughan et al., 2018c;Skilton et al., 2020;Vaughan and Hutson, 2021). Similar to the methodology for N. girellae culture, freshwater L. calcarifer were gradually acclimatised to seawater over 3 days before being introduced into the seawater culture tank (100 l tank). ...
Cleaning symbiosis is critical for maintaining healthy biological communities in tropical marine ecosystems. However, potential negative impacts of mutualism, such as the transmission of pathogens and parasites during cleaning interactions, have rarely been evaluated. Here, we investigated whether the dedicated bluestreak cleaner wrasse Labroides dimidiatus, is susceptible to, and can transmit generalist ectoparasites between client fish. In laboratory experiments, L. dimidiatus were exposed to infective stages of three generalist ectoparasite species with contrasting life-histories. Labroides dimidiatus were susceptible to infection by the gnathiid isopod, Gnathia aureamaculosa, but significantly less susceptible to the ciliate protozoan, Cryptocaryon irritans, and the monogenean flatworm, Neobenedenia girellae, compared to control host species (Coris batuensis or Lates calcarifer). The potential for parasite transmission from a client fish to the cleaner fish was simulated using experimentally transplanted mobile adult (i.e., egg-producing) monogenean flatworms on L. dimidiatus. Parasites remained attached to cleaners for an average of two days, during which parasite egg production continued, but was reduced compared to control fish. Over this timespan, a wild cleaner may engage in several thousand cleaning interactions, providing numerous opportunities for mobile parasites to exploit cleaners as vectors. Our study provides the first experimental evidence that L. dimidiatus exhibits resistance to infective stages of some parasites yet has the potential to temporarily transport adult parasites. We propose that some parasites that evade being eaten by cleaner fish could exploit cleaning interactions as a mechanism for transmission and spread.
... 1.3). Theronts are released from the cysts in the early hours of the morning (Diggles and Lester, 1996;Skilton et al., 2020), before sunrise. Using a dissection microscope, theronts can be observed within the tomonts becoming increasingly active just prior to excystment. ...
... Some mullet species, mollies (Poecilia sphenops) and barramundi (Lates calcarifer) are likely host candidates, the latter being a particularly effective host species which can be managed as a small population (e.g. Skilton et al., 2020;Vaughan et al., 2018). While other non euryhaline marine species can be used, unless their post-infection care includes a rigorous active treatment regime and a quarantine isolation period, the most humane end-point is euthanasia by anaes thetic overdose. ...
This chapter details in vitro methods for the successful culture of Cryptocaryon irritans.
... Such specific responses to light stimuli among these monogenean oncomiracidia are likely parasitic adaptive traits to increase the chance of encountering a suitable fish host. Understanding the innate behaviors of oncomiracidia can be useful for developing new parasite management strategies (e.g., Skilton et al., 2020). Indeed, there have been reports on successful reduction of N. girellae infection in farmed fish using phototaxis of the oncomiracidia (Yamamoto et al. 2014). ...
... Light trap has been proposed as an effective, non-invasive, and environmentally friendly method to monitor and control salmon lice Lepeophtheirus salmonis as its copepodid and adult stages are attracted to LED light (Novales Flamarique et al. 2009;Nordtug et al. 2021). Skilton et al. (2020) also showed that light trap is an effective method to attract Cryptocaryon irritans theronts and N. girellae oncomiracidia, and emphasized its usefulness in aquaculture when used and strategically deployed it to coincide with the emergence of infectious stage. Furthermore, Yamamoto et al. (2014) altered the natural light conditions of farming cages by shading and successfully reduced infection with N. girellae in farmed Scomber japonicus by drawing hatched oncomiracidia away from the fish to outside the culture cage. ...
Phototaxis is the common behavioral response exhibited by the oncomiracidia of various monogeneans. However, the changes in the oncomiracidial swimming behavior in response to light cues are not well understood. Here, we investigated the light responses of four monogeneans that are important pathogens in mariculture, namely Benedenia epinepheli, Benedenia seriolae, Neobenedenia girellae, and Heteraxine heterocerca. The swimming trajectory and speed of oncomiracidia of each species were assessed in a glass Petri dish with an LED light placed adjacent to it, based on three different light responses: LED light in the off position (normal swimming), LED light in the on position (phototactic behavior), and immediately (< 5 s) after switching the LED light off (photophobic behavior). The oncomiracidia of all four species exhibited positive phototactic and photophobic responses; however, the change in swimming speed between each response differed among the species. The oncomiracidia of three species (B. epinepheli, N. girellae, and H. heterocerca) exhibited high swimming speed, as a phototactic response; in contrast, the oncomiracidia of B. seriolae exhibited reduced swimming speed when moving toward the light source. Benedenia epinepheli and H. heterocerca exhibited the highest swimming speed during the phototaxis phase, whereas B. seriolae and N. girellae exhibited the highest swimming speed during the photophobic phase. These light responses are considered adaptive traits to increase the chance of encountering and infecting suitable hosts in nature, and such responses could potentially be applied to the control of parasite infections in aquaculture.
... To overcome these various obstacles, innovations and technologies that are able to increase productivity and sustainability of aquaculture are needed (Mustafa et al., 2021). With the application of bioprocessing, it is hoped that aquaculture can become more efficient, produce high-quality products, and remain environmentally friendly (Skilton et al., 2020). ...
Controlling parasites in cultivated commodities is a crucial challenge in the fisheries industry that can impact fish health and production quality. The use of conventional methods such as chemical drugs often results in negative side effects on the environment and human health. Therefore, the development of bioprocess technology offers a more environmentally friendly and sustainable solution for parasite management. In bioprocess technology, probiotic microorganisms are used to enhance fish immune responses, enzymes such as proteases or lipases are used to lower the number of parasites. Additionally, research also focuses on the development of vaccines to target specific parasites, providing a more permanent control alternative. By reducing reliance on synthetic chemicals and minimizing parasite resistance, these technologies enhance the sustainability of aquaculture. The development and application of this bioprocess technology have the potential to enhance the efficiency and sustainability of aquaculture production. Future research could explore the integration of advanced genetic engineering and microbiome manipulation to enhance the precision and efficacy of bioprocess technologies for parasite control in aquaculture.
... Some of the measures implemented against zoonotic trematodes could also be of value for the control of other parasite-host systems, e.g., preventing parasite eggs from entering the aquaculture facilities or stocking predators or competitors of the intermediate hosts. Since both intermediate hosts and parasites respond to chemical cues in their environment, bait formulations might be developed for the selective removal of these organisms from aquaculture facilities [153,154]. ...
Parasites are very diverse and common in both natural populations and in stocks kept in aquacultural facilities. For most cultured species, there are important bacteria and viruses causing diseases, but eukaryotic parasites are also very important. We review the various combinations of aquacultured species and eukaryotic parasitic groups and discuss other problems associated with aquaculture such as eutrophication, zoonotic species, and invasive species, and we conclude that further development of aquaculture in a sustainable manner must include a holistic approach (One Health) where many factors (e.g., human health, food safety, animal health and welfare, environmental and biodiversity protection and marketability mechanisms, etc.) are considered.
... As such overuse and misuse of veterinary drugs including banned substances has been reported in fish farming (Hashimoto et al. 2011;Girmatsion et al. 2021;Hossain et al. 2022). These practices may stimulate bacterial and parasitic resistance, compromise the safety of seafood intended for human consumption, and pose risks to other aquatic organisms and the environment (Atta et al. 2022;Skilton et al. 2020;Guardone et al. 2022). This context is relevant to the One Health concept, an approach recognizing that human, animal, and environmental health are systemically entwined (Davis and Sharp, 2020). ...
Levamisole, an anthelmintic and immunostimulant drug, has been studied as a promising alternative for aquaculture use. While oral administration through feeding is the main route of administration in fish farming, no studies evaluating methods of levamisole incorporation into the feed have been reported so far. Therefore, this study aimed to evaluate potential procedures for levamisole incorporation in extruded fish feed using ethyl cellulose, gelatin, or vegetable oil, to avoid drug leaching to the water during the animal’s medication. A suitable LC-MS/MS method was optimized (full factorial design), validated, and applied to evaluate the efficiency of the process, the homogeneity of the drug concentration, and the leaching rate. The method has been demonstrated to be selective, precise (RSD < 4.9%), accurate (recovery > 98.4%), and linear (r > 0.99, 125–750 mg kg−1). The incorporation procedures using the three coating agents showed high incorporation efficiency (70%) and a homogeneous drug concentration among the extruded feed pellets. A low levamisole leaching rate was verified in the feed prepared using the ethyl cellulose coating procedure (4.3% after 15 min of immersion in the water). On the other hand, fish feed coated with gelatin and oil resulted in a high leaching rate (30–35% after 15 min). Thus, this study shows that coating ethyl cellulose may be a promising procedure for levamisole incorporation in fish feed and with the potential to enhance its use in animal production while reducing environmental contamination.
... Ectoparasites rely heavily on sensory information to detect and attach to suitable hosts, mostly from chemical (e.g. Kearn 1986;Mikheev et al. 2004;Skilton et al., 2020) and visual (Genna et al. 2005) cues. Gnathiids have also been found to use cues to locate and attach to their hosts. ...
Widespread coral mortality is leading to coral reef degradation worldwide. Many juvenile reef fishes settle on live coral, and their predator-avoidance behaviour is disrupted in seawater exposed to dead corals, ultimately increasing predation risk. Gnathiid isopods are micropredatory fish ectoparasites that occur in higher abundances in dead coral. However, the effect of seawater associated with dead coral on the susceptibility of fish to micropredators has never been investigated. We tested whether the infection rate of cultured gnathiid ectoparasites on individual damselfish, Pomacentrus amboinensis Bleeker 1868, from two different ontogenetic stages (juveniles and adults) was influenced by seawater exposed to three different treatments: dead coral, live coral, or no coral. Seawater treatments were presumed to contain different chemical properties and are meant to represent environmental changes associated with habitat degradation on coral reefs. Gnathiid infection of juvenile fish in seawater exposed to dead coral was twice as high as that of fish in live coral or no coral. Infection rates did not significantly differ between live coral and no coral treatments. In contrast to juveniles, the susceptibility of adults to gnathiids was not affected by seawater treatment. During experiments, juvenile fish mortality was relatively low, but was higher for infected fish (9.7%), compared to fish held without exposure to gnathiids (1.7%). No mortality occurred in adult fish that became infected with gnathiids. Our results suggest that chemical cues released from dead corals and/or dead coral colonisers affect the ability of juvenile, but not adult fish to avoid parasite infection. Considering increased habitat degradation on coral reefs and that gnathiids are more abundant in dead coral substrate, it is possible that wild juvenile fish may experience increased susceptibility to parasitic infection and reduced survival rate. This highlights the importance of including parasitism in ecological studies of global environmental change.
... Gills were removed, separated, and examined for ectoparasites in a dish with seawater using a low-power dissecting microscope; any cysts of potentially parasitic origin were squashed under cover slip pressure and scrutinised using a compound microscope at 20× and 40× magnifications. Fish were then placed into a dish with vertebrate saline for 10 min to remove any potential external parasites susceptible to osmotic shift (Cribb and Bray 2010;Hutson et al. 2018;Skilton et al. 2020). Following external evaluation, the fish were dissected for internal examination. ...
Cleaner fish remove parasites from other organisms, called clients. While there is an extensive body of work on the positive role of cleaners for their clients and reef communities, remarkably, potential parasites hosted by specialised cleaner fishes themselves have not been explored. In this study, we surveyed the parasite community of the Indo-Pacific cleaner wrasse Labroides dimidiatus, and compared it to other wrasses from the same region. L. dimidiatus was found to be infected by eight parasite groups including ectoparasites (copepods, isopods, trichodinids, monogeneans and turbellarians) and endoparasites (myxozoans, trematodes and cestodes) representing at least 12 species. The abundance and prevalence of most parasite groups was comparable to other wrasses, with the exception of bucephalid trematodes, which are not known to infect any other tropical wrasses except for Labroides species. This adds to mounting evidence that some parasite species exhibit atypical life cycles that exploit cleaning symbiosis. Particularly noteworthy was the discovery of gnathiid isopods on L. dimidiatus, which are generally considered the cleaner’s primary food item. Our findings provide new evidence for a potential role of wild cleaner fish as vectors of parasites to new clients, which highlights potential costs associated with cleaning symbiosis.
... Lately, the use of attractants and traps has been suggested as a promising strategy for certain parasites such as sea lice, by exploiting their chemotactic and phototactic responses [14]. Furthermore, a study highlighted the use of urea and light-based traps for controlling the infection by Cryptocaryon irritans and Neobenedenia girellae in aquaculture [15]. However, at present, application of this approach in commercial aquaculture is limited due to the unavailability of efficient traps. ...
Globally, parasites are increasingly being recognized as catastrophic agents in both aquaculture sector and in the wild aquatic habitats leading to an estimated annual loss between 1.05 billion and 9.58 billion USD. The currently available therapeutic and control measures are accompanied by many limitations. Hence, vaccines are recommended as the "only green and effective solution" to address these concerns and protect fish from pathogens. However, vaccine development warrants a better understanding of host-parasite interaction and parasite biology. Currently, only one commercial parasite vaccine is available against the ectoparasite sea lice. Additionally, only a few trials have reported potential vaccine candidates against endoparasites. Transcriptome, genome, and proteomic data at present are available only for a limited number of aquatic parasites. Omics-based interventions can be significant in the identification of suitable vaccine candidates, finally leading to the development of multivalent vaccines for significant protection against parasitic infections in fish. The present review highlights the progress in the immunobiology of pathogenic parasites and the prospects of vaccine development. Finally, an approach for developing a multivalent vaccine for parasitic diseases is presented. Data sources to prepare this review included Pub-med, google scholar, official reports, and websites.
... (2) Impacts on ectoparasites Ectoparasites that have a direct life cycle (i.e., that require only one fish host to complete their development), need to identify, attach to a suitable host, and find a mate (Mordue Luntz 2003;Sharma et al. 2019). Studies investigating which sensory cues are used by ectoparasites in fish farming industries, are gaining more attention (e.g., Devine et al. 2000;Ingvarsdóttir et al. 2002;Genna et al. 2005;Fields et al. 2007;Skilton et al. 2020). For example, the sea louse Lepeophtheirus salmonis on Atlantic salmon (Salmo salar) respond to light intensity due to a relatively highly developed visual system (Flamarique et al. 2000), can detect swimming hosts using water oscillation as mechanical stimuli (Heuch and Karlsen 1997), and can also react to fish odour when reattaching on new hosts (Devine et al. 2000). ...
For the last seven decades, cleaning sym-biosis in the marine environment has been a research field of intrigue. There is substantial evidence that, by removing undesired items from their client fishes, cleaner organisms have positive ecosystem effects. These include increased fish recruitment, abundance and enhanced fish growth. However, the intimate association and high frequency of interactions between cleaners and clients potentially facilitates pathogen transmission and disease spread. In this review, we identify knowledge gaps and develop novel hypotheses on the interrelationship between parasites, hosts and the environment (disease triangle concept), with a particular emphasis on the potential role of cleaner organisms as hosts and/or transmitters of parasites. Despite evidence supporting the positive effects of cleaner organisms, we propose the cleaners as transmitters hypothesis; that some parasites may benefit from facilitated transmission to cleaners during cleaning interactions, or may use cleaner organisms as transmitters to infect a wider diversity and number of hosts. This cost of cleaning interactions has not been previously accounted for in cleaning theory. We also propose the parasite hotspot hypothesis; that parasite infection pressure may be higher around cleaning stations, thus presenting a conundrum for the infected client with respect to cleaning frequency and duration. The impact of a changing environment, particularly climate stressors on cleaners' performance and clients' cleaning demand are only beginning to be explored. It can be expected that cleaners, hosts/cli-ents, and parasites will be impacted in different ways by anthropogenic changes which may disrupt the long-term stability of cleaning symbiosis.
... Traps use attractants e.g. urea, light, host mucus to exploit various behaviours and cues at specific life stages and trap and prevent subsequent escape of the species (Skilton et al., 2020). To the best of our knowledge parasite trapping has never been applied to blood flukes or other trematode larvae. ...
Fish blood flukes (Digenea: Aporocotylidae) are important pathogens of fishes in aquaculture. Severe infections have been associated with mass mortality events in cultured marine species of teleosts in Australia, Asia and Europe, leading to significant socio-economic losses. Here we review recent advances towards understanding the biology and ecology of fish blood flukes, and the integral role molecular techniques have played in this development. Techniques include molecular matching of aporocotylid life stages using ITS-2 rDNA, and targeting ITS-2 rDNA to distinguish aporocotylid species using quantitative PCR (qPCR). These approaches have facilitated the elucidation of multiple life cycles for species of Cardicola infecting bluefin tunas Thunnus spp. cultured in Australia and Japan. Continued work to identify intermediate hosts of fish blood flukes is critical to improve understanding of their life cycles and help inform aquatic animal health management e.g. through site selection and/or separation of intermediate and definitive hosts. As praziquantel is the only known treatment option for infected fish, its continued efficacy will need to be monitored and other possible solutions may need to be identified as aquaculture continues to grow and diversify.
Biofloc technology (BFT), initially adapted for shrimp farming in the 1970s, represents a sophisticated ecosystem of microorganisms designed to enhance aquaculture productivity and sustainability. Despite its established history, research into BFT is surprisingly still at an early stage globally. This review conducted a bibliometric analysis of 612 articles from major aquaculture journals spanning 2008–2023 to systematically explore the development, trends, and focal points of BFT research. The analysis revealed that the bulk of significant contributions originates from Brazil and China, and highlighting areas of interest can be categorized into four hotspots, such as (1) efficient nitrogen transformation, (2) biofloc microbiology, (3) biofloc's immunostimulant properties, and (4) the evaluation of research methodologies. At the end, the microecology concept was introduced, and the cross‐discipline methods were promoted in the aquaculture field. Notably, much of the BFT research is still at an exploratory phase, with numerous functional bacteria unidentified and optimization strategies for BFT underdeveloped. These gaps present opportunities for enhancing aquaculture through improvements in wastewater management, product quality, safety, and yield. Furthermore, the review notes a growing trend in applying microbiome research and microecological analysis in aquaculture, with high‐throughput sequencing data increasingly used to understand microbial interactions and nitrogen transformation within bioflocs. This direction promises to unlock further insights into the complex microbial ecosystems of bioflocs and their applications in sustainable aquaculture.
A decision support tool was developed to aid management of problematic parasites in marine fish aquaculture. The tool provides biologically relevant treatment intervals to interrupt the life cycle of ectoparasitic flatworms that occur in global kingfish and amberjack (Seriola spp.) aquaculture. Temperature‐dependent life cycle parameters for the ‘skin flukes’, Benedenia seriolae and Neobenedenia girellae, and the ‘gill fluke’, Zeuxapta seriolae, were derived from published data and modelled using non‐linear regressions. Increasing temperatures shortened the duration of most life cycle parameters of all parasites. Salinity had no effect on the timing of life cycle parameters but limited hatching success in hypo‐ and hypersaline conditions. The tool, named BeNeZe after the first two letters of each parasite genera, enables rapid determination of treatment intervals for two consecutive medicinal immersion or ‘bathing’ treatments—the first to kill adult flatworms attached to fish and the second to prevent maturity of new parasite recruits. As temperature increases, the interval between treatments and the ‘window’ within which the second treatment should be applied is reduced. The tool can be used for multi‐species infections. The inclusion of parasite taxonomy, biology and behaviour as part of an integrated management strategy is reviewed. Available through an open access app, BeNeZe is intended to be applied in conjunction with farm biosecurity, surveillance, management measures and recognition of independent management units. BeNeZe can be used to reduce infection burdens, improve fish welfare and production and reduce treatment number and frequency.
Macroalgal cultivation is expanding rapidly, and promises to contribute significantly towards future food and energy security, sustainable livelihoods, ecosystem services and habitat provisioning for a range of associated organisms globally. Habitat provisioning underpins biodiversity and ecosystem structure and functioning, supports many ecosystem services and has possible benefits to other marine industries, including enhancement of commercial fish stocks. In macroalgal cultivation, however, only recently has habitat provisioning started to be assessed at a local scale (within a farm's footprint) and with a range of different approaches. This review evaluates techniques used to quantify habitat provisioning in and around macroalgal cultivation sites, for species ranging from microorganisms to megafauna, and outlines recommendations to enable a more comprehensive ecological valuation of macroalgal cultivation in the future. The majority of information on biodiversity associated with macroalgal cultivation is associated with quantifying biofouling or pest organisms, rather than the contribution of colonising species to healthy ecosystem functioning. We suggest how better monitoring of macroalgal cultivation could enable an ecosystem approach to aquaculture (EAA) in the future. To achieve this, we highlight the need for standardised and robust methods for quantifying habitat provisioning that will enable assessment and monitoring of macroalgal cultivation sites of varying scales and within different regions and environmental settings. Increased evidence for the potential habitat value of macroalgal cultivation sites will help inform and shape marine legislation, licencing and certification for macroalgal farmers and potentially reduce marine user conflicts, helping the industry to continue to grow sustainably using EAA.
Almost all living things need to be able to move, whether it is toward desirable environments or away from danger. For vector-borne parasites, successful transmission and infection require that these organisms be able to sense where they are and use signals from their environment to direct where they go next, a process known as chemotaxis. Here, we show that Trypanosoma brucei , the deadly protozoan parasite that causes African sleeping sickness, can sense and move toward an attractive cue. To our knowledge, this is the first report of positive chemotaxis in these organisms. In addition to describing a new behavior in T. brucei , our findings enable future studies of how chemotaxis works in these pathogens, which will lead to deeper understanding of how they move through their hosts and may lead to new therapeutic or transmission-blocking strategies.
In present study, the data of pesticide use, crop (the total of cereals, pulses, roots and tubers, oil crops, fibre
crops, fruits, vegetables, and melons, etc.) production and the area harvested of the world and major countries
for the period between 1990 and 2014 were collected, organized and summarized from FAOSTAT. First I
proposed an index to measure the productive efficiency of pesticide use, cost / benefit, which refers to the
amount of pesticide use to produce a certain amount of crop in a year. Theoretical relationship between crop
yield and cost / benefit of pesticide use is a model with the sigmoid curve: y = a + b / (1 + e^(c-rx)), where y is
crop yield, x is cost / benefit of pesticide use. The results showed that global cost / benefit of pesticide use
(total) increased with time during 1990 to 2007, and declined since 2007. Pesticide use (total) (kg / ha) had the
similar trend. Global insecticides, herbicides, and fungicides & bactericides use and cost / benefit declined
with time since 2007. During 2010 and 2014, mean pesticide cost / benefit was 0.645 g pesticide use (total) /
kg crop production, and mean annual pesticide use (total) was 2.784 kg /ha. Mean cost / benefit of insecticides,
herbicides and fungicides & bactericides use between 2010 and 2014 were 0.051, 0.16 and 0.074 g / kg crop
production, respectively, and mean annual use of insecticides, herbicides and fungicides & bactericides were
0.221, 0.69 and 0.32 kg / ha, respectively. Globally, the cost / benefit of dithiocarbamates, bipiridils,
carbamates insecticides, and organo-phosphates, and the use of dithiocarbamates, bipiridils, and carbamates
insecticides have significantly declined since 2007, and conversely, the cost / benefit of triazoles / diazoles and
the use of triazoles / diazoles, plant growth regulators, and amides, have significantly increased since 2007. Of
the major countries, the averaged annual cost / benefit of pesticide use (total) of Brazil during 2010 to 2014
was the greatest (1.883), followed by Japan (1.846), Mexico (1.678), China (1.243), Canada (0.979), USA
(0.8733), France (0.708), Germany (0.673), UK (0.55), and India (0.089). The averaged annual pesticide use
(total) (kg / ha) of Japan during 2010 to 2014 was the greatest (18.94), followed by China (10.45), Mexico
(7.87), Brazil (6.166), Germany (5.123), France (4.859), UK (4.034), USA (3.886), and India (0.261). Profile
of development, production and use of pesticides in China was discussed in detail. Various trends were
analysed and a variety of valuable data were provided.
http://www.iaees.org/publications/journals/piaees/articles/2018-8(1)/global-pesticide-use-Profile-trend-cost-benefit.pdf
Background:
Most odour baits designed to attract host-seeking mosquitoes contain carbon dioxide (CO2), which enhances trap catches, given its role as a mosquito flight activator. However, the use of CO2 is expensive and logistically demanding for prolonged area-wide use.
Methods:
This study explored the possibility of replacing organically-produced CO2 with 2-butanone in odour blends targeting host-seeking malaria mosquitoes. During semi-field and field experiments MM-X traps were baited with a human odour mimic (MB5 blend) plus CO2 or 2-butanone at varying concentrations. Unbaited traps formed a control. The attraction of Anopheles gambiae s.s., Anopheles arabiensis and Anopheles funestus to these differently baited traps was measured and mean catch sizes were compared to determine whether 2-butanone could form a viable replacement for CO2 for these target species.
Results:
Under semi-field conditions significantly more female An. gambiae mosquitoes were attracted to a reference attractant blend (MB5 + CO2) compared to MB5 without CO2 (P < 0.001), CO2 alone (P < 0.001), or a trap without a bait (P < 0.001). Whereas MB5 + CO2 attracted significantly more mosquitoes than its variants containing MB5 plus different dilutions of 2-butanone (P = 0.001), the pure form (99.5%) and the 1.0% dilution of 2-butanone gave promising results. In the field mean indoor catches of wild female An. gambiae s.l. in traps containing MB5 + CO2 (5.07 ± 1.01) and MB5 + 99.5% 2-butanone (3.10 ± 0.65) did not differ significantly (P = 0.09). The mean indoor catches of wild female An. funestus attracted to traps containing MB5 + CO2 (3.87 ± 0.79) and MB5 + 99.5% 2-butanone (3.37 ± 0.70) were also similar (P = 0.635). Likewise, the mean outdoor catches of An. gambiae and An. funestus associated with MB5 + CO2 (1.63 ± 0.38 and 0.53 ± 0.17, respectively) and MB5 + 99.5% 2-butanone (1.33 ± 0.32 and 0.40 ± 0.14, respectively) were not significantly different (P = 0.544 and P = 0.533, respectively).
Conclusion:
These results demonstrate that 2-butanone can serve as a good replacement for CO2 in synthetic blends of attractants designed to attract host-seeking An. gambiae s.l. and An. funestus mosquitoes. This development underscores the possibility of using odour-baited traps (OBTs) for monitoring and surveillance as well as control of malaria vectors and potentially other mosquito species.
Cleaning symbiosis has been documented extensively in the marine environment over the past 50 years. We estimate global cleaner diversity comprises 208 fish species from 106 genera representing 36 families and 51 shrimp species from 11 genera representing 6 families. Cleaning symbiosis as originally defined, is amended to highlight communication between client and cleaner as the catalyst for cooperation, and to separate cleaning symbiosis from incidental cleaning, which is a separate mutualism preceded by no communication. Moreover, we propose the term “dedicated” to replace “obligate” to describe a committed cleaning lifestyle. Marine cleaner fishes have dominated the cleaning symbiosis literature, with comparatively little focus given to shrimp. The engagement of shrimp in cleaning activities has been considered contentious because there is little empirical evidence. Plasticity exists in the use of “cleaner shrimp” in the current literature, with the potential to cause significant confusion. Indeed, this term has been used incorrectly for the shrimp Infraorder Stenopodidea, involving three families, Stenopodidae, Palaemonidae, and Hippolytidae, and to represent all members of Lysmata and Stenopus. Caution is expressed in the use of grey literature and anecdotal observations to generate data on cleaning interactions, due to the presence of species complexes. Interest in cleaning organisms as biological controls in aquaculture is increasing due to their value as an alternative to various chemical ectoparasite controls. Reports of the importance of cleaner organisms in maintaining a healthy reef ecosystem has also been increasing and we review the current biological knowledge on cleaner-organisms, highlighting areas that are understudied.
Farming of Atlantic salmon has grown rapidly from its start in the early 1970s until today, with production approaching two million tonnes. Sea cages are the dominant production system for the on-growing stage of salmon farming. It represents an effective production system with lower investment and running costs than land-based systems. The development and improvement of the sea cage farming system has been one of the most important factors for the growth of the salmon farming industry. However, during recent years certain problems related to their placement in the open marine environment have proved highly challenging, increasing operating costs and impacting on industry public relations. The problems are mainly due to parasites, diseases and escape of fish. In this article, emerging technical solutions for solving those problems are described.
The infection dynamics and distribution of the ectoparasitic fish monogenean Neobenedenia sp. (Monogenea: Capsalidae) throughout its development was examined on barramundi, Lates calcarifer (Bloch) (Latidae), by labelling transparent, ciliated larvae (oncomiracidia) with a fluorescent dye. Replicate fish were each exposed to approximately 50 fluorescent oncomiracidia and then examined for parasites using an epifluorescence stereomicroscope at 10 time intervals post-exposure (15, 30, 60, 120 min, 24, 48 h, four, eight, 12, and 16 days). Fluorescent labelling revealed that parasites attached underneath and on the surface of the scales of host fish. Parasite infection success was 20% within 15 min, and peaked at 93% two days post-exposure, before gradually declining between four and sixteen days. Differences in parasite distribution on L. calcarifer over time provided strong evidence that Neobenedenia sp. larvae settled opportunistically and then migrated to specific microhabitats. Parasites initially attached (<24 h) in greater mean numbers on the body surface (13 ± 1.5) compared to the fins (4 ± 0.42) and head region (2 ± 0.41). Once larvae recruitment had ceased (48 h), there were significantly higher mean post-larvae counts on the head (5 ± 3.4) and fins (12 ± 3) compared to previous time intervals. Neobenedenia sp. aggregated on the eyes, fins, and dorsal and ventral extremities on the main body. As parasites neared sexual maturity, there was a marked aggregation on the fins (22 ± 2.35) compared to the head (4 ± 0.97) and body (9 ± 1.33), indicating that Neobenedenia sp. may form mating aggregations.
The aquaculture of Atlantic salmon Salmo salar faces severe health, environmental and economic concerns caused by the parasitic sea lice Lepeophtheirus salmonis and Caligus spp. An experimental delousing method exists whereby the surface jumping behaviours of salmon are combined with a floating, oil-infused chemical therapeutant, resulting in the fish dousing themselves passively. We tested whether a light stimulus or feed event, or a combination of both, during submergence (denial of surface access for the fish) increased the surface-oriented behaviours of salmon. Groups of 10 salmon were submerged in a sea-cage for 19 h and exposed to a light stimulus, feed event, or both. Control treatments involved submergence only. For a 2 h period after surface access was reinstated, light and feed treatments induced a higher proportion of individuals to exhibit surface behaviours. On average, 84 and 82% of salmon in the light and feed treatments jumped, respectively, which was 1.6 times higher than fish in the control group (50%). Salmon exposed to light or feed jumped an average of 1.7 and 1.5 times after exposure to light or feed treatments, respectively, compared to 0.92 jumps fish(-1) for the control. The combined light and feed treatment did not produce a synergistic effect. The average time until first jump was 31 to 50 min, with no difference in times among treatments. The elevated surface-oriented behaviours effectively crowded the majority of the fish in the surface waters within a short period of time. This increased surface activity may be used for a range of salmon farming applications, including improving the efficacy of sea-lice treatment techniques.
Under laboratory conditions at 25°C, the monogenean Neobenedenia girellae (Hargis, 1955) rapidly developed on Japanese flounder (Paralichthys olivaceus), and it took 15-17 days from egg to maturation.The whole process of egg formation from the release of oocytes from the germiduct to laying of egg capsule required a mean of 73sec. At room temperatures between 27-30°C, large adults laid a mean of 35.4eggs/h, while smaller ones a mean of 12.2eggs/h. Eggs began to hatch after incubation for 5-6 days at 25°C with natural cycle of illumination, but no hatching occurred at 15°C. It took 10-11 days to reach sexual maturity where the minimum body size for an egg-laying adult was 2.1mm. When compared with other benedeniine species, N.girellae required a shorter time and a smaller body size to attain maturity and showed a high level of egg output. One-day old larvae were found only on the fins of Japanese flounder.As the parasites grew, they were found not only on the fins but most commonly on the dorsal and ventral body surface of fish, suggesting migration of the parasite from the fins.
Fish monogeneans are lethal parasites in aquaculture. We provide the first experimental evidence that a notorious fish monogenean, Neobenedenia sp., can produce viable eggs in isolation for three consecutive generations. We infected individual, isolated, farmed barramundi, Lates calcarifer (Bloch) with a single oncomiracidium (larva) of the hermaphroditic monogenean Neobenedenia sp. Isolated parasites reached sexual maturity at day 10 post-hatch (24°C, 35‰) and laid ∼3,300 embryonated eggs over 17 days. Egg production rapidly increased following sexually maturity on day 10 (58±15 eggs) and peaked on day 15 (496±68 eggs) before gradually decreasing. Neobenedenia sp. exhibited egg laying and egg hatching rhythms. Parasites laid eggs continuously, but egg production increased in periods of darkness (64.3%), while the majority of oncomiracidia (81%) emerged from eggs in the first three hours of light. Eggs laid by isolated 'parent' parasites hatched and individual emerging oncomiracidia were used to infect more individual, isolated fish, with three consecutive, isolated, parasite generations (F1, F2 and F3) raised in the laboratory. Infection success and egg hatching success did not differ between generations. Our data show that one parasite, in the absence of a mate, presents a severe threat to captive fish populations.
While jellyfish are some of the most ancient multicellular organisms on earth, man only started to take notice of their impact on human activity and enterprise from about the 1960s. In some regions of the world, jellyfish blooms impose considerable socio-economic hardship to net-based fisheries, aquaculture, power generation and tourism. Blooms are likely to be difficult if not impossible to eradicate, but these industries are striving to develop management strategies that will enable them to successfully coexist with blooms. This chapter reviews the detrimental effects that jellyfish have on society and human wellbeing. We also summarise adaptation and management strategies that are currently being developed and utilised by fishing, power generation and tourism industries to educate and inform the public and manage the actual jellyfish blooms and help ensure the financial viability of these industries in regions that experience blooms.
Insects are able to see ultraviolet (UV) radiation. Nocturnal insects are often attracted to light sources that emit large amounts of UV radiation, and devices that exploit this behavior, such as light traps for forecasting pest outbreaks, and electric insect killers, have been developed. Some diurnal species are attracted to yellow; yellow pan traps are used for conducting surveys for pest outbreaks and yellow sticky plates are used for pest control. Lamps that give off yellow illumination have been used effectively to control the activity of nocturnal moths and thus reduce damage to fruit, vegetables, and flowers. Covering cultivation facilities with film that filters out near-UV radiation reduces the invasion of pests such as whiteflies and thrips into the facilities, thus reducing damage. Reflective material placed on cultivated land can control the approach of flying insects such as aphids. Future development and use of new light sources such as light-emitting diodes is anticipated for promoting integrated pest management.
We conducted a series of experiments to understand the behavioral characteristics of oncomiracidium of the monogenean Heterobothrium okamotoi and compared them with those of two other monogenean species, Heteraxine heterocerca and Neobenedenia girellae. Behavior of H. okamotoi oncomiracidium consisted of two alternate phases: a swimming phase with strong ciliary beatings and a stationary phase with ciliary beatings too weak to generate any movements. The duration of one swimming-stationary cycle considerably varied among individuals but tended to increase with larval age. During the 5-day monitoring, length of the swimming phase decreased while that of the stationary phase tended to increase as the larva became older. The locomotion patterns differed significantly among individuals, but as a whole, larvae showed random horizontal movement and no phototactic reaction. The oncomiracidium tended to move downward because it was heavier than seawater and also swam downward at the start of the swimming phase because its anterior part pointed downward when the larva was not swimming. Those behavioral characteristics of larval H. okamotoi are likely to have evolved in order to maximize the chance of encountering its benthic fish host, tiger puffer Takifugu rubripes.
Light-dependent behavior of the abundant zooplankton species inhabiting the White Sea were studied experimentally during: (i) the spring equinox (March); (ii) the polar day (late May to June), (iii) August, 17/7 h day–night light cycle, (iv) the fall equinox (October). Behavioral patterns were investigated for eight species of Copepoda (Metridia longa, Calanus glacialis, Pseudocalanus minutus, Oithona similis, Oncaea borealis, Temora longicornis, Centropages hamatus, Acartia spp.), one Cladocera species (Evadne nordmanni) and Polychaeta larvae. The hypothesis was tested that attraction to (or repulsion from) light is the primary mechanism involved in the vertical migration of zooplankton with different trophic characteristics in relation to phytoplankton-rich upper water layer. The impact of red (680 nm), yellow (560 nm) and UV (280 nm) light was tested. The animals were acclimated to two food conditions: natural seawater (satiated) and filtered (1 µm) seawater (hungry). The positive light response of predominantly herbivorous and omnivorous copepods and cladocerans inhabiting the photic water layer corresponds with their distribution and their food vertical distribution. Hungry animals display the strongest responses to light. Light effects on behavior were weak in deep-dwelling O. borealis. We suggest that red and yellow light is an indicator of the photic layer (high food concentration) to zooplankton groups that feed on phytoplankton. In contrast, diapausing (e.g. non-feeding) copepods totally avoid light, especially when they hibernate in the aphotic layer. We hypothesize that there is a relationship between the light response of the zooplankton, their trophic characteristics, migration behavior (diel and ontogenetic) and the water layer occupied.
Palm weevils in the subfamily Rhynchophorinae (Curculionidae) (Rhynchophorus spp., Dynamis borassi, Metamasius hemipterus, Rhabdoscelus obscurus, and Paramasius distortus) use male-produced aggregation pheromones for intraspecific chemical communication. Pheromones comprise 8, 9, or 10 carbon, methyl-branched, secondary alcohols. (4S,5S)-4-Methyl-5- nonanol (ferrugineol) is the major aggregation pheromone for R. ferrugineus, R. vulneratus, R, bilineatus, M. hemipterus, and D. borassi and a minor component for R. palmarum. (5S,4S)-5-Methyh-4-octanol (cruentol), (3S,4S)- 3-methyl 4-octanol (phoenicol) and (4S,2E)-6-methyl-2-hepten-4-ol (rhynchophorol) are the main aggregation pheromones for R. cruentatus, R. phoenicis, and R. palmarum, respectively. Plant kairomones strongly enhance pheromone attractiveness but none of the identified volatiles, such as ethyl acetate, ethyl propionate, or ethyl butyrate are as synergistic as fermenting plant (palm or sugarcane) tissue. Studying orientation behavior of foraging weevils to semiochemical devices helped to design and test traps for weevil capture. Generally, 3 mg per day of synthetic pheromone (with non-natural stereoisomers being benign) plus insecticide-treated plant tissue constitute highly attractive trap baits. Potential exists for pheromone-based mass-trapping of weevils to reduce their populations and the spread of the weevil-vectored red ring disease, for monitoring their population dynamics to facilitate pest management decisions, and for detection and possible interception of non-native weevils at ports of entry.
Sea lice are ectoparasitic copepods that threaten salmon farming aquaculture and the viability of wild salmon populations. To control infestations on farmed salmon, several chemotherapeutants have been developed, but these are invasive (often causing fish stress and loss in production), costly, may induce parasite resistance over time, and their impact on the environment is a major social concern. Here, we show that a light-emitting diode (LED)-based light trap can be used to monitor sea lice presence on fish and in the water. The performance of the light trap was tested in experimental tanks and in the ocean. Plankton net tows were also performed to compare catches with those from light traps. The light trap caught ~70% of salmon lice larval stages loaded onto a tank and ~24% of the adults. It also acted as a delousing agent by removing ~8% of adult salmon lice infective on Chinook salmon (Oncorhynchus tshawytscha) smolts in tank experiments. In the ocean, the light trap caught 21 sea lice (10 Lepeophtheirus salmonis and 11 Caligus clemensi), comprising free-swimming and attached stages, while plankton net tows failed to capture any. We conclude that light traps constitute an effective, noninvasive, environmentally friendly method to monitor sea lice.
An inexpensive automated light-trap has shown great potential as a tool for quantifying spatial and temporal patchiness in assemblages of larval fishes. Automation means that simultaneous samples can be collected within narrow time-windows from multiple locations. With the right sampling design, synoptic maps of larval abundance can be produced with a resolution equivalent to the density of traps. Because the traps do not kill like other techniques, it is far easier to resolve the distributions of individual species and the live larvae can be used for further experimentation. Some data from Lizard Island, northern Great Barrier Reef, are reported to demonstrate the utility and the limitations of this technique.
Cryptocaryon irritans Brown 1951, a holotrichous ciliate parasite of marine fishes, causes marine white spot disease. In aquaria, C. irritans can cause acute damage and heavy mortalities to marine teleosts. Although first described 60 years ago, only within the last decade has detailed information emerged concerning its life cycle, transmission and pathogenesis. An update of our knowledge of this important aquarium fish parasite is presented here.
Accurate identification of parasite species and strains is crucial to mitigate the risk of epidemics and emerging disease. Species of Neobenedenia are harmful monogenean ectoparasites that infect economically important bony fishes in aquaculture worldwide, however, the species boundaries between two of the most notorious taxa, N. melleni and N. girellae, has been a topic of contention for decades. Historically, identifications of Neobenedenia isolates have overwhelmingly been attributed to N. melleni, and it has been proposed that N. girellae is synonymous with N. melleni. We collected 33 Neobenedenia isolates from 22 host species spanning nine countries and amplified three genes including two nuclear (Histone 3 and 28S rDNA) and one mitochondrial (cytochrome b). Four major clades were identified using Maximum Likelihood and Bayesian inference analyses; clades A-D corresponding to N. girellae, N. melleni, N. longiprostata and N. pacifica respectively. All unidentified isolates and the majority of Neobenedenia sequences from GenBank fell into clade A. The results of this study indicate that N. girellae is a separate species to N. melleni, and that a large proportion of previous samples identified as N. melleni may be erroneous and a revision of identifications is needed. The large diversity of host species that N. girellae is able to infect as determined in this study and the geographic range in which it is present (23.8426° S and 24.1426° N) makes it a globally cosmopolitan species and a threat to aquaculture industries around the world.
Global expansion in fish production and trade of aquatic ornamental species requires advances in aquatic animal health management. Aquatic parasite cultures permit diverse research opportunities to understand parasite–host dynamics and are essential to validate the efficacy of treatments that could reduce infections in captive populations. Monogeneans are important pathogenic parasites of captured captive fishes and exhibit a single-host life cycle, which makes them amenable to in vivo culture. Continuous cultures of oviparous monogenean parasites provide a valuable resource of
eggs, oncomiracidia (larvae) and adult parasites for use in varied ecological and applied scientific research. For example, the parasite–host dynamics of Entobdella soleae (van Beneden and Hesse, 1864) and its fish host, Solea solea (Linnaeus, 1758), is one of the most well-documented of all monogeneans following meticulous, dedicated study. Polystoma spp. cultures provide an intriguing model for examining evolution in monogeneans because they exhibit two alternative phenotypes depending on the age of infection of amphibians. Furthermore, assessments of the ecological, pathological
and immunological effects of fish parasites in aquaculture have been achieved through cultures of Gyrodactylus von Nordmann, 1832 spp., Benedenia seriolae (Yamaguti, 1934), Neobenedenia Yamaguti, 1963 spp. and Zeuxapta seriolae (Meserve, 1938). This review critically examines methods to establish and maintain in vivo monogenean monocultures on finfish, elasmobranchs and amphibians. Four separate approaches to establish cultures are scrutinised including the collection of live infected hosts, cohabiting recipient hosts with infected stock, cohabiting hosts with parasite eggs or oncomiracidia (larvae) and direct transfer of live adult parasites onto new fish hosts. Specific parasite species’ biology and behaviour permits predictive collection of parasite life stages to effectively maintain a continuous culture, while environmental parameters can be altered to manipulate parasite generation time. Parasite virulence and biosecurity are
vital components of a well-managed culture to ensure appropriate animal welfare and uncontaminated surrounding environments. Contemporary approaches and techniques are reviewed to ensure optimised monogenean cultures, which ultimately can be used to further our understanding of aquatic parasitology and identify mechanisms to limit infestations in public aquaria, ornamental trade and intensive aquaculture.
Agricultural insects and stored-product insects are influenced by luminance intensities, exposure times, and wavelengths of light-emitting diodes (LEDs). Based on the phototactic behaviors of the agricultural insects, green or blue LEDs are most attractive for Bemisia tabaci, Trialeurodes vaporariorum, Myzus persicae, Liriomyza trifolii, Spodoptera exigua, and Spodoptera litura. Green LED attracts Plutella xylostella and Frankliniella occidentalis. Similarly, green or blue LEDs are more attractive to agricultural insects, such as Liriomyza sativae, Sogatella furcifera, and Nilaparvata lugens, than other wavelength LEDs. Concerning the phototactic behaviors of the stored-product insects, red LED is attractive for, in descending order Tribolium castaneum, Sitophilus zeamais, Lasioderma serricorne, and Tyrophagus putrescentiae. Blue LED captures most Sitophilus oryzae and Sitotroga cerealella. Red and blue LEDs are more attractive for stored-product insect pests rate than ultraviolet LED and green, yellow, white, and infrared LEDs. Based on the attraction rate of the stored-product insects on granary, red LED is most attractive for S. cerealella and Plodia interpunctella. These light sources are effective in controlling agricultural and stored-product insects. Applying LED technology for greenhouses and granaries along with conventional traps reduces crop loss due to moths, beetles, aphids, and weevils. LEDs have potential value in integrated pest management.
The effects of high temperature on the parasitic stage (trophont) and encysted stage (tomont) of Cryptocaryon irritans were examined. The effects on trophonts were examined by rearing fish artificially infected with C. irritans at 25, 28, 31 or 34°C. The effects on tomonts were examined by incubating tomonts at the same temperatures. In these experiments, both the trophonts and tomonts showed normal developments below 31°C, whilst their development was badly damaged at 34°C. The effects of dissolved oxygen on tomont development were examined. Tomonts were incubated in hyperoxic (141%), oxic (100%), hypoxic (24%) and anoxic (0%) conditions. Under the hypoxic and hyperoxic conditions, tomont development was suppressed. Under the anoxic condition, tomonts died. However, when tomonts were transferred into an oxic condition after 2 or 4- week incubation in the hypoxic condition, development resumed, showing a rapid increase in theront excystment rates 10 to 11 days after the transfer. These results show a possibility that the supply of oxygen into water bottom along with the disappearance of thermoclines is involved in the autumn outbreaks of cryptocaryoniasis of cultured marine fish in floating net cages located in inner bays.
Effective parasite management can be achieved through strategically timed treatments that break the life cycle. We examined the effects of temperature (2 °C increments from 22 to 34 °C) and salinity (0, 11, 22, 35, 40 ‰) on the life cycle (embryonation period, hatching success, oncomiracidia (larvae) longevity, infection success, and time to sexual maturity) of Neobenedenia sp. (Monogenea: Capsalidae), a harmful ectoparasite of farmed marine fishes. Experiments were conducted in controlled conditions in the laboratory. The life cycle was faster in warm, high saline conditions compared to cooler conditions (10-13 days between 26-32 °C, 40 ‰; 15-16 days between 22-24 °C at 40 ‰). Warm seawater and high saline conditions (24-32 °C, 35-40 ‰) improved egg hatching success, reduced time to sexual maturity, and resulted in parasites reaching sexual maturity at a larger size (at 30-32 °C) compared to cooler conditions (22 °C). In contrast, cool, hypersaline conditions (22 °C, 40 ‰) increased oncomiracidia longevity and infection success. Linear and quantile regression models were used to construct an interactive, online parasite management interface to enable strategic treatment of parasites in aquaculture corresponding to observed temperature and salinity variation on farms in the tropics. It was recommended that farmers treat their stock more frequently during summer (27-31 °C) when parasites can complete their life cycle more quickly. Nevertheless, farmers should be aware of the potential for increased Neobenedenia sp. infections during winter months (21-26 °C) due to increased infection success.
Cryptocaryon irritans is a parasitic ciliate that causes major economic losses in marine fish aquaculture globally. Despite the wide array of treatment methods, control of cryptocaryoniasis is still very challenging, especially in food fish culture. Thus, additional control methods against this parasite might be required to further reduce the occurrence of this disease. In this study, the swimming ability, excystment sequence, and distribution of theronts, the infective stage of C. irritans, were investigated in our effort to develop a physical control strategy. A video analysis for assessing the swimming ability of theronts showed diminishing mobility over time. The excystment of theronts primarily occurred during the dark period. Examination of the vertical distribution of theronts showed that they were mostly distributed at the 5 cm sampling point measured from the substrate, indicating that they have low upward swimming ability. From these results, we conclude that theronts possess limited mobility. Theronts also displayed an excystment pattern that might be influenced by photoperiod, since most theronts were released during the dark period of the day. Control strategies can be developed from these properties, such as increasing the water flow in a culture tank during the release period. Further, combined treatment methods against multiple stages of C. irritans can help minimize the occurrence of cryptocaryoniasis in culture facilities.
Light traps were used to sample small fish and squid from open waters in the central Great Barrier Reef lagoon. A total of 7203 fish, representing some 38 families, and 706 lologinid squid were caught during sampling periods October to January, 1988 to 1990. The fish catch was dominated by the family Pomacentridae (63 % of fish collected), with lower numbers of lethrinids (6.7 %), clupeids (6.3 %), mullids (3.8 %), and scombrids (2.7 %). Size-frequencies of the fish collected indicated that the light traps sampled late-stage larvae and pelagic juveniles exclusively. No effect of time of night on catch rate was detected. Light traps that were allowed to drift with prevailing water currents caught more fish than anchored traps; this unexpected result may be a function of the effect of current velocity on trap efficiency. Analysis of standard error/sample size curves suggested that optimum replication was achieved with 5 to 6 traps, but that reasonable precision could be obtained with 2 to 3 traps. Coefficients of variation among replicate traps were taxon-specific, ranging from 0.9 (for clupeids) to 0.2-0.1 (for pomacentrids). These values compare favourably with those obtained from trawl nets. Light traps have considerable potential for sampling nekton that are capable of avoiding conventional towed nets.
The skin fluke Neobenedenia girellae has become a serious problem in Japan since the 1990s. Present control methods focus on the removal of the attached parasite and these post-infection treatments are often labor intensive, time consuming, and/or stressful to fish. Chub mackerel Scomber japonicus are highly susceptible to N. girellae. However, because of their sensitive nature, bath treatments may cause mortality. In this study, we investigated the efficacy of cage shading to reduce skin fluke infection and the frequency of conventional post-infection treatments. Juvenile mackerel were reared in cages with or without shade for 3 months and their skin fluke infections were monitored. We performed either freshwater baths or oral administration of praziquantel if fluke intensity exceeded the given criteria. In unshaded cages, 3 total bath treatments or 6 total drug treatments were conducted. In contrast, no treatment was required for the shaded cage. The overall fluke intensity in the shaded cage was less than half that of the unshaded cages, despite the lack of treatments. This study demonstrated for the first time the practical use of shading in fish farms to reduce skin fluke infection.
Skin fluke infection is a major parasitic problem in the aquaculture industry. Present control measures such as bath treatments are effective for removing flukes from fish but require extensive labour and time. Moreover, bath treatments cause great stress to the fish, and occasionally lead to post-treatment mortality. Our ultimate goal is to develop a culture technique that prevents or lowers the chance of fish encountering larval skin flukes, thus reducing infection. However, little is known about when and where these infections occur on fish farms. We conducted a field experiment at a culture site to determine the diurnal pattern of skin fluke infection at different water depths. Juvenile amberjack, Seriola dumerili, were placed in enclosed mesh cages and exposed to skin flukes at depths of 0, 2 or 4 m for 4 h during different times of the day. A Neobenedenia girellae infection occurred predominantly at the surface during the mid-day. The infection rate declined considerably during the night. The parasite burden was significantly decreased with water depth, and up to an 80% and 95% reduction in intensities was observed when fish were exposed at a depth of 2 and 4 m, respectively. These results suggest that skin fluke infection can be significantly reduced by systematic management strategy and modification of culture techniques.
Concurrent infections provoked by the sea lice Lepeophtheirus simplex and the monogenean Neobenedenia sp. on bullseye puffer fish Sphoeroides annulatus, reared in tanks, have been related to skin pathology and mortality. Freshwater treatment is widely used to treat two parasite groups, but the results differ depending on the parasite species, life stage and exposure time. The present study describes the effectiveness of freshwater treatments to remove both parasites. Sea lice nauplii and free swimming copepodids, reared in the laboratory, were exposed to freshwater treatments for periods from 30 s to 16 min. Fish experimentally infected with sea lice or monogeneans were exposed to freshwater for 15 to 90 min and 10 to 60 min, respectively. All sea lice nauplii and copepodids were killed by freshwater dips at 2.5 and 14 min, respectively. For pre-adult and adult sea lice, 30 and 60 min of freshwater exposure significantly reduced up to 95 and 99% respectively. However, most freshwater exposures did not reduce chalimus stages more than 10%. Immature and adult populations of monogeneans showed a significant reduction of 95% at 20 min of exposure. These results indicate that, if used properly, freshwater baths constitute an efficient alternative to control these mixed ectoparasite infections on bullseye puffer fish reared in tanks.
Epizootics of the holotrichous ciliate, Cryptocaryon irritans, have impeded monoculture of red snapper, Lutjanus campechanus, at the Florida Department of Natural Resources facilities in St. Petersburg, Florida. Cryptocaryoniasis was associated with most mortalities and was controlled only in one group of red snapper being conditioned for induced spawning. An effective treatment regime which has prevented recurring Cryptocaryon infections included hypersalinity, quinine hydrochloride, chloroquine, and minimal handling.
The primary function of fish skin is to act as a barrier. It provides protection against physical damage and assists with the maintenance of homoeostasis by minimising exchange between the animal and the environment. However in some fish, the skin may play a more active physiological role. This is particularly true in species that inhabit specialised environmental niches (e.g. amphibious and air-breathing fish such as the lungfish), those with physiological characteristics that may subvert the need for the integument as a barrier (e.g. the osmoconforming hagfish), and/or fish with anatomical modifications of the epidermis (e.g. reduced epithelial thickness). Using examples from different fish groups (e.g. hagfishes, elasmobranchs and teleosts), the importance of fish skin as a transport epithelium for gases, ions, nitrogenous waste products, and nutrients was reviewed. The role of the skin in larval fish was also examined, with early life stages often utilising the skin as a surrogate gill, prior to the development of a functional branchial epithelium.
Information on gregarious settlement and metamorphosis of larvae is reviewed for cirripedes, echiuroids, sabellarid polychaetes, and echinoids to determine if the use of adult-derived chemical cues is consistent with the concept of pheromonal communication as applied to other types of animals. Examples of several species of marine invertebrates in which adult-derived chemical cues may be utilized in gregarious settlement and metamorphosis are listed. In appears this mechanism of habitat selection is similar in many respects to communication common in insects and vertebrates where chemicals released to the environment elicit behavioral, physiological, or developmental responses from conspecifics. Evidence is not available to determine if this form of communication in marine invertebrates has specialized beyond adaptive responses of larvae to adult-associated chemicals, to true chemical signalling.
Trapped common carp Cyprinus carpio display a pronounced escape behavior of jumping out of the water; this behavior is not exhibited by most Australian native fishes. Hence, there appears to be an important opportunity to exploit the unique jumping behavior of nonnative common carp to aid selective removal. We report on the Williams cage, a simple device that automatically separates jumping common carp from nonjumping fish. Between November 2002 and April 2005, the Williams cage was tested at Torrumbarry Weir fishway on the Murray River, Victoria, Australia, and trapped fish were counted every 24 h. The Williams cage successfully separated 88% of adult common carp into a confinement area. In contrast, more than 99.9% of 8,031 native fish passed through the Williams cage and exited the fishway. The Williams cage may provide a method for controlling dispersal and abundance of common carp and may be applicable to other nuisance fish species.
From a critical review of the literature, it is concluded that the role of carbon dioxide in host-seeking by mosquitoes comprises two distinct actions. Firstly, it acts as an ‘attractant’, orientation towards the host being mediated by kinesis and optomotor anemotaxis. When tested in the absence of moving air currents, orientation to the source is not possible and only the kinetic or ‘activating’ effect is manifested. Moreover, in the absence of other host factors, sustained flight takes place only in response to intermittent pulses of carbon dioxide; this response is not elicited in uniformly permeated airstreams. Secondly, carbon dioxide has a combined action with warm moist convection currents at close range and with odour factors at a distance from the host.
The ciliate Cryptocaryon irritans Brown, 1951 is a parasite of tropical marine fishes, being recorded chiefly from coral reef species (Laird, 1956; Burgess, 1978; Colorni, 1985). The disease, cryptocaryosis, accounts for fish mortalities in aquaria (De Graaf, 1973) and mariculture systems (Huff & Burns, 1981; Colorni, 1985; Kaige & Miyazaki, 1985; Rasheed, 1989); however, relatively few studies have been undertaken on the biology of C. irritans, as highlighted by Lorn & Dykova (1992). Sikama (1937) described the major features of the life cycle, infection of the fish epidermis alternating with a free-living phase of reproduction within a protective cyst. Most other investigations of C. irritans have been concerned with morphology (Sikama, 1937, 1938; Brown, 1951, 1963; Nigrelli & Ruggieri, 1966; Cheung et al., 1981; Colorni, 1988) with a recent work on the ultrastructure of the pellicle (Matthews et al., 1993). Little is known regarding the behaviour of free-living stages and the possible influence of environmental factors on transmission. Nigrelli & Ruggieri (1966) noted photopositive responses in theronts. The establishment and maintenance of C. irritans in mullet under controlled conditions (Burgess & Matthews, 1994) provided an opportunity further to investigate light in the survival strategy of this fish pathogen.
Productivity of crops grown for human consumption is at risk due to the incidence of pests, especially weeds, pathogens and animal pests. Crop losses due to these harmful organisms can be substantial and may be prevented, or reduced, by crop protection measures. An overview is given on different types of crop losses as well as on various methods of pest control developed during the last century.
Estimates on potential and actual losses despite the current crop protection practices are given for wheat, rice, maize, potatoes, soybeans, and cotton for the period 2001–03 on a regional basis (19 regions) as well as for the global total. Among crops, the total global potential loss due to pests varied from about 50% in wheat to more than 80% in cotton production. The responses are estimated as losses of 26–29% for soybean, wheat and cotton, and 31, 37 and 40% for maize, rice and potatoes, respectively. Overall, weeds produced the highest potential loss (34%), with animal pests and pathogens being less important (losses of 18 and 16%). The efficacy of crop protection was higher in cash crops than in food crops. Weed control can be managed mechanically or chemically, therefore worldwide efficacy was considerably higher than for the control of animal pests or diseases, which rely heavily on synthetic chemicals. Regional differences in efficacy are outlined. Despite a clear increase in pesticide use, crop losses have not significantly decreased during the last 40 years. However, pesticide use has enabled farmers to modify production systems and to increase crop productivity without sustaining the higher losses likely to occur from an increased susceptibility to the damaging effect of pests.
The concept of integrated pest/crop management includes a threshold concept for the application of pest control measures and reduction in the amount/frequency of pesticides applied to an economically and ecologically acceptable level. Often minor crop losses are economically acceptable; however, an increase in crop productivity without adequate crop protection does not make sense, because an increase in attainable yields is often associated with an increased vulnerability to damage inflicted by pests.
Mediterranean fruit fly (Ceratitis capitata Weidemann, ‘Medfly’) is currently distributed only in Western Australia. Although occasional detections occur in South Australia and the Northern Territory, they invoke a comprehensive and rapid response to prevent establishment. Medfly previously occurred on the eastern coast of mainland Australia. However, it is believed to have been displaced by Queensland fruit fly (Bactrocera tryoni Froggatt, ‘Qfly’), with the last recorded finding of Medfly in 1941 for New South Wales and 1953 in Victoria. Tasmania has not documented any incursions of Medfly since 1920 and the Northern Territory eradicated the last incursion in 1994. In contrast, Qfly is regularly found in parts of Queensland, New South Wales, Victoria, and the Northern Territory. A species closely related to Qfly, B. aquilonis (May), is established in the Northern Territory and northern Western Australia. Occasional detections of Qfly in South Australia and southern Western Australia result in immediate regulatory actions and eradication activities to ensure that it does not become established. South Australia, Tasmania and the Fruit Fly Exclusion Zone are free from fruit flies of economic concern. Any detections of pest fruit fly species in these areas are immediately quarantined and eradicated. The distribution of Qfly has remained largely unchanged for the last half-century, with established populations along the eastern States and the Northern Territory. The Medfly distribution has also remained unchanged for the last half-century. Qfly and Medfly do not currently co-exist in Australia. This is likely because of the differences in egg-laying habits, competition by larvae in fruit and differences in host range. A similar displacement of Ceratitis by Bactrocera has occurred in other parts of the world.
Adult male sea lice Lepeophtheirus salmonis were more likely to leave host fish Atlantic salmon Salmo salar if they detected the chemical cues of other adult male lice than if they detect cues of female lice. The detection of both male and female chemical cues yielded an intermediate response. These results suggest that males use chemical cues to balance competition for resources and mate acquisition, and they highlight the need for further studies of the chemical ecology of this important parasite.
The influence of light and/or fish on the behaviour of the infective stage of Ichthyophthirius multifiliis was investigated in an aquarium (30 × 10 × 7,5 cm) divided by a net into two equal compartments in the following experiments: 1. illuminated versus darkened compartment, 2. compartment with fish versus compartment without fish and 3. combinations of 1. and 2. After 45 to 70 minutes, significantly more theronts were found in the illuminated compartment than in the darkened one. When adding a fish to one of the two illuminated compartments, the number of theronts was significantly lower in the compartment containing the fish. The combination of tight and fish factors revealed significantly more theronts in the illuminated area with no fish than in the darkened area containing one fish. However, no difference occurred between the number of theronts in an illuminated area with fish and a darkened one without fish. These findings allow the suggestion that theronts show a positive phototaxis but no active search for fish.
Laboratory experiments were conducted to determine the effect of salinity on embryonic development and hatching in Neobenedenia melleni, a monogenean ectoparasite of seawater-cultured (37 ppt) Florida red tilapia (Oreochromis urolepis hornorum × O. mossambicus). Eggs, collected from adult monogeneans at 37 ppt, were exposed to different salinities (0, 6, 12, 18, 24, 30 and 37 ppt) for 48, 72 or 96 h. Varying degrees of post-treatment development and hatching occurred when natural seawater conditions were restored. Hatching success generally declined with decreasing salinity and increasing duration of exposure. Under all durations of exposure, hatching success remained relatively high (≥ 69.6%) at salinities of 24 ppt and above, but declined markedly (≤ 32.5%) at lower salinities. Hatching did not occur in eggs exposed to fresh water (0 ppt) for 72 and 96 h. The most effective treatments in preventing hatching, other than prolonged exposure to fresh water, were 96 h exposures to low-salinity brackish water. Percent hatch after 96 h exposure to 6, 12 and 18 ppt was 5.5, 11.9 and 5.8%, respectively.
This study investigated: 1) the influence of water temperature on Neobenedenia girellae (capsalid) infection, parasite growth, egg production and emerging second generation on the host amberjack Seriola dumerili (Carangidae) in Experiment I, and 2) changes in the infection level of N. girellae on S. dumerili, and the parasite growth and histopathological changes of S. dumerili skin infected with N. girellae at different water temperatures in Experiment II. In Experiment I, the length of parasites from S. dumerili reared at 30 °C was significantly greater than parasites from fish reared at 20 °C or 25 °C. Parasite eggs were observed at 13 days from larval attachment at 20 °C, 8 days at 25 °C, and 6 days at 30 °C, thus the number of eggs laid by parasites from S. dumerili reared at 30 °C was greater than that from fish reared at 20 °C and 25 °C. The next generation N. girellae larvae were identified on fish reared at 25 °C and 30 °C at 13 days after exposure to oncomiracidia and the number of larval parasites on fish reared at 30 °C was significantly higher than that on fish reared at 25 °C. In Experiment II, at 8 days and 12 days after exposure to oncomiracidia, the differences in the number of parasites among fish reared at 20 °C, 25 °C and 30 °C were not statistically significant. However, the number of parasites on fish reared at 30 °C was significantly lower than that on fish reared at 20 °C and 25 °C at 16 days after the exposure, suggesting that their life span after larval attachment on the host was shorter with increasing water temperature and ability of the parasites to infect on the host was comparable among these temperatures. Seriola dumerili epidermis with attached N. girellae thinned markedly in groups reared at 25 °C and 30 °C, whereas the epidermis of S. dumerili in the group reared at 20 °C did not, compared with that of uninfected fish throughout the trial. Therefore, at higher water temperatures, frequent measures for controlling the parasites would be required. Any information on N. girellae life cycle is potentially important in developing a strategy for its control.
A standardized procedure for Cryptocaryon irritans propagation was established by means of infecting the animal model pompano Trachinotus ovatus (167.8 ± 15.1 g) with a sub-lethal dose of theronts. By using this method, up to 40 consecutive cycles were successively established. Briefly, theronts collected within 2 h of excystment were used to infect pompanos (8000–15,000 theronts per fish) in dark for 3 h starting between 22:00 and 24:00, at 27 ± 0.5 °C and 29–32‰ salinity. The trophonts on the skin and gill appeared evidently 60 h post-infection. Their growth phase culminated when the mature trophonts spontaneously exited the host after another 24 h and fell to the bottom as protomonts. All of the protomonts were collected by using a special collection unit. After a 60-h incubation, the protomonts evolved into tomonts and began to release theronts. The excystment of theronts reached the peak after 24 h, and at this time point the theronts were collected for the next cycle of propagation. One cycle of propagation took one week and produced approximately 1 million theronts per fish. The maximum parasite yield of propagation was 122-fold and the minimum was 61-fold. The longest survival time of theronts was 36 h. The infection rate of theronts upon excystment was 64%, and then declined evidently by 4 h. At 8 h, the infection rate declined to 9.6%. The present study demonstrated that C. irritans could be efficiently propagated on T. ovatus, a suitable experimental host. The standardized method for C. irritans propagation provides a foundation for future studies of C. irritans such as its pathogenicity and control of the disease it causes.
Intraspecific variation in the ciliate Cryptocaryon irritans was examined using sequences of the first internal transcribed spacer region (ITS-1) of ribosomal DNA (rDNA) combined with developmental and morphological characters. Amplified rDNA sequences consisting of 151 bases of the flanking 18 S and 5.8 S regions, and the entire ITS-1 region (169 or 170 bases), were determined and compared for 16 isolates of C. irritans from Australia, Israela and the USA. There was one variable base between isolates in the 18 S region nd 11 variables indicate that Australian C. irritans isolates from estuarine (Moreton Bay) and coral reef (Heron Island) environments are distinct. The Heron Island isolate was genetically closer to morphologically dissimilar isolates from Israel (1.8% divergence) and USA (2.3 % divergence) than it was to the Moreton Bay isolates. Three isolates maintained in our laboratory since February 1994 originated from the same source. During this time the sequence of the isolates from wild fish in Moreton Bay remained unchanged. These genetic differences indicate the existence of a founder effects in laboratorty populations of C. irritans. The genetic variation found here, combined with known morphological and developmental differences, is used to characterise four strains of C. irritans.
The population fluctuation of the red palm weevil, Rhynchophorus ferrugineus was studied, using the aggregation pheromone traps, during 2000 and 2001 in the United Arab Emirates. The insect population
increased gradually from January to reach its peak in March, April, or May. The populations in three date palm plantations
were much less in 2001 compared to 2000 with reductions of 29.7–51.7%. An evaluation of the performance of the pheromone traps
showed that they could capture 4.4 to 20.7% of the resident populations of R. ferrugineus in the three different date palm plantations. No significant differences could be found in rates of capture between males
and females. Individuals of marked weevils released in date palm plantations migrated 1–7km from the plantations in which
they were released. The released marked weevils were recaptured, mostly, within 3–5days post release.
Two field studies were carried out with farmed Atlantic salmon (Salmo salar L.) in sea cages to examine various effects of artificial light (AL) and the vertical distribution of salmon on lice infestation.The use of AL light caused an overall increase in lice infestation in both experiments. The first study showed that salmon held at 0–4 m depth in cages developed higher infestation than salmon held at greater depths (4–8 and 8–12 m) under both natural light (NL) and AL. In the second study, salmon maintained in 14-m deep sea cages that were exposed to AL with different light intensities. The AL treatments resulted directly in different diel and seasonal patterns of vertical distribution of the salmon and also different temporal patterns in lice infestations. So indirectly the infestation pattern appeared to be correlated with median day-time swimming depth of the salmon.