Fish Behavior Research Articles

Anglers as potential vectors of aquatic invasive species: Linking inland water bodies in the Great Lakes region of the US.

Unimpeded transfer and spread of invasive species throughout freshwater systems is of global concern, altering species compositions, disrupting ecosystem processes, and diverting economic resources. The magnitude and complexity of the problem is amplified by the global connectedness of human movements and the multiple modes of inter-basin transport of aquatic invasive species. Our objective was to trace the fishing behavior of anglers delineating potential pathways of transfer of invasive species throughout the vast inland waters of the Great Lakes of North America, which contain more than 21% of the world's surface freshwater and are among the most highly invaded aquatic ecosystems in the world. Combining a comprehensive survey and a spatial analysis of the movements of thousands of anglers in 12 states within the US portion of the Great Lakes Basin and the Upper Mississippi and Ohio River Basins, we estimated that 6.5 million licensed anglers in the study area embarked on an average of 30 fishing trips over the course of the year, and 70% of the individuals fished in more than one county. Geospatial linkages showed direct connections made by individuals traveling between 99% of the 894 counties where fishing occurred, and between 61 of the 66 sub-watersheds in a year. Estimated numbers of fishing trips to individual counties ranged from 1199-1.95 million; generally highest in counties bordering the Great Lakes. Of these, 79 had more than 10,000 estimated fishing trips originating from anglers living in other counties. Although angler movements are one mechanism of invasive species transfer, there likely is a high cumulative probability of invasive species transport by several million people fishing each year throughout this extensive freshwater network. A comprehensive georeferenced survey, coupled with a spatial analysis of fishing destinations, provides a potentially powerful tool to track, predict, curtail and control the transfer and proliferation of invasive species in freshwater.

The Roles of Histamine Receptor 1 (hrh1) in Neurotransmitter System Regulation, Behavior, and Neurogenesis in Zebrafish

Histamine receptors mediate important physiological processes and take part in the pathophysiology of different brain disorders. Histamine receptor 1 (HRH1) is involved in the development of neurotransmitter systems, and its role in neurogenesis has been proposed. Altered HRH1 binding and expression have been detected in the brains of patients with schizophrenia, depression, and autism. Our goal was to assess the role of hrh1 in zebrafish development and neurotransmitter system regulation through the characterization of hrh1−/− fish generated by the CRISPR/Cas9 system. Quantitative PCR, in situ hybridization, and immunocytochemistry were used to study neurotransmitter systems and genes essential for brain development. Additionally, we wanted to reveal the role of this histamine receptor in larval and adult fish behavior using several quantitative behavioral methods including locomotion, thigmotaxis, dark flash and startle response, novel tank diving, and shoaling behavior. Hrh1−/− larvae displayed normal behavior in comparison with hrh1+/+ siblings. Interestingly, a transient abnormal expression of important neurodevelopmental markers was evident in these larvae, as well as a reduction in the number of tyrosine hydroxylase 1 (Th1)–positive cells, th1 mRNA, and hypocretin (hcrt)-positive cells. These abnormalities were not detected in adulthood. In summary, we verified that zebrafish lacking hrh1 present deficits in the dopaminergic and hypocretin systems during early development, but those are compensated by the time fish reach adulthood. However, impaired sociability and anxious-like behavior, along with downregulation of choline O-acetyltransferase a and LIM homeodomain transcription factor Islet1, were displayed by adult fish.

Evaluating blood, gill, and muscle biopsy methods on the behaviour, reproductive success, and survival of a wild freshwater fish

Non-lethal biopsy methods (including blood, gill, and muscle biopsies) have been used to study the health and physiological status of wild fishes. Nonetheless, concerns exist regarding the impact of non-lethal sampling on relevant welfare measures such as behaviour and survival. Here, nesting Smallmouth Bass (Micropterus dolomieu) were used as a model species to study in situ how fish respond to non-lethal sampling. Male Smallmouth Bass provide sole parental care and guard well-defined nests for a period of several weeks, providing a unique opportunity to assess behaviour, reproductive success, and survival in the wild. Fish were captured from their nests by angling and subjected to a biopsy (either blood, gill, or muscle), or a combination of all three biopsy methods prior to release. A control group that was captured but not biopsied as well as a non-angled control were also included. Nests were monitored for a period of four weeks or until the parental males either abandoned offspring, died, or raised a brood to independence. Single biopsies, regardless of the biopsy type, were found to have no impact on parental care and survival, but fish that received the combined treatment took longer to return to their nest and displayed a 6.5 times greater likelihood of nest abandonment. Mortality was only observed in fish that received the combined biopsy treatment. As such, this study reveals that it is possible to maintain the welfare status of Smallmouth Bass in the wild by using individual biopsies, thus emphasizing the importance of making careful decisions about which tissues are needed to achieve desired study objectives. This is one of the few studies to assess the behavioural and fitness consequences of increasingly common non-lethal biopsy methods and provides useful information on the relative consequences of different biopsy methods on wild fish.

Bioenergetic consequences of repeated catch-and-release fisheries interactions on adult steelhead across a range of ecologically relevant water temperatures

The biological consequences of catch-and-release angling have been studied for decades, yet little is known about the compounding effects of repeated recreational fisheries recaptures on the physiology and behaviour of angled fish. Using heart rate biologgers and behavioural assays, this study investigated the physiological and behavioural consequences of multiple simulated angling events (i.e., repeated stressors) on female steelhead (Oncorhynchus mykiss), under current (6 °C) and future (11 °C) water temperature scenarios. While steelhead in the warmer water temperature scenario demonstrated alterations in cardiac function (e.g., increases in maximum heart rate and scope of heart rate) and evidence of behavioural impairments (e.g., decreases in chase activity and landing time) over the course of two simulated angling events, cold water treated fish had negligible change. Fish subjected to two simulated angling events under warm water temperature conditions tended to demonstrate an increase in recovery time and scope for heart rate, and a decrease in resting heart rate. A second experiment was conducted to test for sex-specific differences in the heart rate response of steelhead subjected to an increase in water temperature. Females demonstrated a higher scope for heart rate when compared to males during the event and during recovery. More work is needed to better understand the interaction between multiple angling events and recovery from these events at various water temperatures, and the biological basis for sex-specific differences in cardiac function and response to challenges. This study contributes to a growing body of evidence on the effects of repeated stressors on wild fish.

FIRST REPORTS OF LIGULA INTESTINALIS AND A SCHISTOCEPHALUS SP. INFECTING SMALL-BODIED FISH IN NEW BRUNSWICK, CANADA.

Morphological characteristics and DNA sequencing were used to identify plerocercoids of a Schistocephalus sp. infecting slimy sculpin (Cottus cognatus) from northern New Brunswick and plerocercoids of Ligula intestinalis infecting blacknose dace (Rhinichthys atratulus) in Fundy National Park (FNP, New Brunswick). To our knowledge, no previous publications documented either cestode from New Brunswick, Canada. Blacknose dace represent a new host record for L. intestinalis. Identifications were made based on the presence or absence of segmentation and sequencing partial nicotinamide adenine dinucleotide dehydrogenase subunit 1 (ND1; mitochondrial DNA) and/or partial cytochrome c oxidase subunit 1 (COI; mitochondrial DNA). Plerocercoids from blacknose dace in FNP were identified as Ligula intestinalis based on >99% nucleotide identity with COI for this species in the NCBI GenBank database. Plerocercoids in slimy sculpin from northern New Brunswick were identified as a Schistocephalus sp. based on high nucleotide identity with congenerics in the NCBI GenBank database. The absence of GenBank entries with sufficient high percent identity to our specimens, and potential species hybrids in this genus, prevents species-level identification of Schistocephalus sp. plerocercoids currently. The absence of previous documentation of these cestodes might reflect recent environmental change promoting the transmission of these parasites that can modulate host fish behavior, induce sterility of host fishes, and contribute to epizootics.

Kinematics and behaviour in fish escape responses: guidelines for conducting, analysing and reporting experiments.

Work carried out since the late 1970s has provided key insights into the comparative biomechanics, kinematics, behaviour and neurobiology of fish escape responses. An escape response is an ecologically important behaviour used by fishes to evade predation and aggression via rapid swimming movements. With environmental change expected to affect the physiology and biomechanics of aquatic ectotherms, there is a growing interest in understanding how environmental stressors affect the swimming performance and behaviour of fishes during escape responses, particularly in the context of predator-prey interactions. As the study of fish swimming continues to expand, there have been repeated calls to standardise experiments and reporting practices to facilitate integrative and comparative studies. Here, we provide a set of practical guidelines for conducting, analysing and reporting experiments on escape responses in fish, including a reporting checklist to assist authors undertaking these experiments. These resources will facilitate executing and reporting escape response experiments in a rigorous and transparent fashion, helping to advance the study of fish swimming in an era of rapid environmental change.

Studies on Effects of Chronic Exposure of Some Organophosphates to Catla catla (HaM.)

The present study deals with the long-term toxic effects of the lowest sub-lethal concentration of dimethoate and malathion on a freshwater fish Catla catla. Toxicity is measured in terms of inhibition in acetylcholinesterase activity and fish behaviour. Technical grades of dimethoate (30 EC) and malathion (50 EC) were used for the present study. LC50 values for 96 hours were calculated for both pesticides. The lowest sublethal concentration (1/5 of LC50) of both pesticides was taken for chronic exposure. As organophosphates are potent inhibitors of acetylcholinesterase (AChE) activity, the AChE activity was estimated by the method of Metcalf (1957) in the brain and liver tissue of the test fishes to evaluate chronic toxicity. The fish were observed regularly to analyse the changes in behaviour. A significant increase in inhibition of acetylcholinesterase activity was observed. Experimental fishes exhibited a decreased rate of opercular movement, loss of balance, excessive mucous secretion, erratic swimming, and increased surfacing with increasing exposure time. Probable reasons for these alterations have been discussed in detail.

Ecotourism impacts on reef fishes in a marine reserve during the COVID‐19 era

Marine reserves generally permit ecotourism within their boundaries as a source of income for local communities, but the impacts of ecotourism on wildlife are still poorly understood. The lockdown resulting from the COVID‐19 pandemic in 2020 provided a unique opportunity to evaluate wildlife diversity in the absence of human activity. In a marine reserve in Mexico, we monitored fish assemblages before, during, and immediately after the lockdown to examine ecotourism impacts on fish assemblages. Our results show that fish density rose 2.5‐fold during the lockdown, suggesting that ecotourism activities alter fish behavior. We suggest that the presence of divers and noise pollution generated by recreational vessels are important disturbance factors. In the absence of human activity, however, some fish may be more bold (hide less often) or may return to the reserve after having retreated to more tranquil (deepwater) areas. We hope that our findings spur efforts to improve the health of marine reserves through the establishment of effective management strategies to mitigate ecotourism impacts.

The Need for Reporting Rationale and Detailed Methods in Studies that Surgically Implant Fish with Electronic Tracking Devices

Each year, thousands of fishes are tagged with electronic devices to study their biology and inform fisheries management. Such research assumes that the process of capturing, tagging, and then holding fish to allow them to recover before release (i.e., the “tagging process”) does not alter the physiology, behavior, and survival of these fish. However, the fish can experience physiological challenges during the tagging process that may affect their behavior and survival. We have observed that the rationale used to establish protocols for holding durations and conditions of fish before and following surgery has received little attention. Here, we provide a perspective that: (1) provides an overview of the tagging process and its effects on the physiology, behavior, and survival of fish; (2) highlights the diverse holding conditions and durations used by researchers (that are often inadequately described and seem arbitrary); and (3) identifies key research needs. We conclude that decisions of whether, how, and for how long to hold tagged fish before release depend on diverse circumstances that need to be evaluated by researchers. We recommend that researchers explicitly report the details of how, when, where, and why tagged fish are held to facilitate protocols that benefit fish welfare, science, and management.

How sexual and natural selection interact and shape the evolution of nests and nesting behaviour in fishes.

Among ray-finned fishes that provide parental care, many spawn in constructed nests, ranging from bowls, burrows and ridges to nests made of algae or bubbles. Because a nest by definition is a construction that enhances the nest-builder's fitness by helping it meet the needs of the developing offspring, nest-building behaviour is naturally selected, as is a preference for spawning with mates that provide well-built nests. However, nest-building behaviour can also be sexually selected, when nest traits increase mating success, protect against sperm competition or nest take-overs by conspecifics. Here, we offer a systematic review, with examples of how competition for sites and location of fish nests relates to sexual selection. We examine direct and indirect benefits of mate choice linked to nest traits, and different types of nests, from a sexual selection perspective. Nest-related behaviours are often under both natural and sexual selection, and we disentangle examples where that is the case, with special attention to females. We highlight some taxa in which nest building is likely to be sexually selected, but lack of research has left them uninvestigated. Some of them are established aquarium species, making them particularly amenable for future research. Finally, we compare with arthropods, amphibians and birds. This article is part of the theme issue 'The evolutionary ecology of nests: a cross-taxon approach'.

High uncertainty in fish bioenergetics impedes precision of fish-mediated carbon transport estimates into the ocean’s twilight zone

Mesopelagic fishes may contribute substantially to marine carbon transport by consuming organic carbon near the surface at night and releasing it in the mesopelagic zone during the day. However, the magnitude and uncertainties associated with this transport are not well understood; fish-mediated carbon flux estimates range from less than 1 % to greater than 30 % of biologically-driven carbon export out of the epipelagic zone. While total mesopelagic fish biomass is an important source of uncertainty, information on fish bioenergetics and movement might also limit the precision of carbon transport estimates. Here, we ask how uncertainties in fish bioenergetics and behaviors affect carbon flux estimation, and which processes contribute most to uncertainty. We used sensitivity analyses to reveal that modeled carbon flux was most sensitive to respiration-related parameters, and per capita fish carbon flux estimates varied six-fold over the range of plausible parameter values. Biomass estimation can add at least ten-fold variation in ecosystem-scale carbon flux estimates. We conclude that it is not currently possible to estimate fish-mediated carbon flux precisely, but estimates may be constrained through future empirical work on the most influential parameters.

Is vision deterioration responsible for changes in the host’s behavior caused by eye flukes?

Trematodes localizing in the lenses of fish change the behavior of their hosts. These behavioral changes are widely suggested to be parasitic manipulations of host behavior aimed at increasing the possibility of eye flukes completing their life cycle. It is often assumed that fish change their behavior due to the vision deterioration caused by trematode larvae. We checked this assumption by testing Salvelinus malma infected with eye flukes (Diplostomum pseudospathaceum) under different lighting conditions. We suggested that if the parasite alters the host’s behavior through vision impairment, then in the dark (when fish do not rely on vision to navigate), the difference in the behavior of infected and uninfected fish would disappear. Eye flukes, indeed, changed fish behavior, making their hosts less vigilant. We believe this is the first evidence of possible parasitic manipulation in this study system. However, contrary to expectations, the difference in the behavior of infected and control fish was independent of the lighting conditions. Our results suggest that mechanisms of behavioral change other than vision impairment should be taken into account in this fish-eye fluke study system.

Influence of Methylene Blue or Dimethyl Sulfoxide on Larval Zebrafish Development and Behavior.

The use of larval zebrafish developmental testing and assessment, specifically larval zebrafish locomotor activity, has been recognized as a higher throughput testing strategy to identify developmentally toxic and neurotoxic chemicals. There are, however, no standardized protocols for this type of assay, which could result in confounding variables being overlooked. Two chemicals commonly employed during early-life stage zebrafish assays, methylene blue (antifungal agent) and dimethyl sulfoxide (DMSO, a commonly used vehicle) have been reported to affect the morphology and behavior of freshwater fish. In this study, we conducted developmental toxicity (morphology) and neurotoxicity (behavior) assessments of commonly employed concentrations for both chemicals (0.6-10.0 μM methylene blue; 0.3%-1.0% v/v DMSO). A light-dark transition behavioral testing paradigm was applied to morphologically normal, 6 days postfertilization (dpf) zebrafish larvae kept at 26°C. Additionally, an acute DMSO challenge was administered based on early-life stage zebrafish assays typically used in this research area. Results from developmental toxicity screens were similar between both chemicals with no morphological abnormalities detected at any of the concentrations tested. However, neurodevelopmental results were mixed between the two chemicals of interest. Methylene blue resulted in no behavioral changes up to the highest concentration tested, 10.0 μM. By contrast, DMSO altered larval behavior following developmental exposure at concentrations as low as 0.5% (v/v) and exhibited differential concentration-response patterns in the light and dark photoperiods. These results indicate that developmental DMSO exposure can affect larval zebrafish locomotor activity at routinely used concentrations in developmental neurotoxicity assessments, whereas methylene blue does not appear to be developmentally or neurodevelopmentally toxic to larval zebrafish at routinely used concentrations. These results also highlight the importance of understanding the influence of experimental conditions on larval zebrafish locomotor activity that may ultimately confound the interpretation of results.

Acute mancozeb-fungicide exposure induces neuro-ethology disruption, health disorders, and immune-oxidative dysfunction in Nile tilapia (Oreochromis niloticus)

An acute exposure study of mancozeb (MAZ) fungicide was applied on Oreochromis niloticus for 96-h duration. Three hundred fish (20.50 ± 1.60 g) were assigned into six groups (50 fish/ group; 10 fish/replicate) and exposed to different six concentrations (0, 4, 8, 12, 16, and 20 mg L−1) of MAZ for 96-h. The Probit analysis program was used to compute the 96-h lethal concentration 50 (96-h LC50) of MAZ. During the exposure duration, the fish's behavior, clinical symptoms, and mortalities were recorded daily. After the exposure period was ended, the hematological, biochemical, immunological, and oxidant/antioxidant parameters were evaluated. The results of this study recorded the 96-h LC50 of MAZ for O. niloticus to be 11.49 mg L−1. Acute MAZ exposure badly affected the fish's behavior in the form of increased the breath gasping and swimming activity with aggressive mode. The exposed fish showed excessive body hemorrhages and fin rot. The survival rate of the exposed fish to MAZ was 100, 80, 66, 50, 38, and 30% in 0, 4, 8, 12, 16, and 20 mg L−1 MAZ, respectively. The hematological indices (red blood cell count, hemoglobin, packed cell volume%, and white blood cell count) were significantly decreased by increasing the MAZ exposure concentration (8–20 mg L−1). The acetylcholine esterase activity and immune indices (lysozyme, nitric oxide, immunoglobulin M, complement 3) were decreased by MAZ exposure (4–20 mg L−1). Acute MAZ exposure induced hepato-renal dysfunction and elevated stress-related parameter (cortisol) by increasing the MAZ concentration. A significant reduction in the antioxidant parameters (total antioxidant activity, catalase, and superoxide dismutase) with increasing the lipid peroxidation marker (malondialdehyde) was noticed by acute MAZ exposure (4 –20 mg L−1) in O. niloticus. Based on these outcomes, the MAZ exposure induced toxicity to the fish evident in changes in fish behavior, neurological activity, hepato-renal functioning, and immune-antioxidant responses which suggest physiological disruption.

Individual variation in preference behavior in sailfin fish refines the neurotranscriptomic pathway for mate preference.

Social interactions can drive distinct gene expression profiles which may vary by social context. Here we use female sailfin molly fish (Poecilia latipinna) to identify genomic profiles associated with preference behavior in distinct social contexts: male interactions (mate choice) versus female interactions (shoaling partner preference). We measured the behavior of 15 females interacting in a non-contact environment with either two males or two females for 30 min followed by whole-brain transcriptomic profiling by RNA sequencing. We profiled females that exhibited high levels of social affiliation and great variation in preference behavior to identify an order of magnitude more differentially expressed genes associated with behavioral variation than by differences in social context. Using a linear model (limma), we took advantage of the individual variation in preference behavior to identify unique gene sets that exhibited distinct correlational patterns of expression with preference behavior in each social context. By combining limma and weighted gene co-expression network analyses (WGCNA) approaches we identified a refined set of 401 genes robustly associated with mate preference that is independent of shoaling partner preference or general social affiliation. While our refined gene set confirmed neural plasticity pathways involvement in moderating female preference behavior, we also identified a significant proportion of discovered that our preference-associated genes were enriched for 'immune system' gene ontology categories. We hypothesize that the association between mate preference and transcriptomic immune function is driven by the less well-known role of these genes in neural plasticity which is likely involved in higher-order learning and processing during mate choice decisions.

Structure of Aggressive Behavior in Underyearlings of the Rainbow Trout Oncorhynchus mykiss (Salmonidae) Changes under the Influence of Diplostomum pseudospathaceum (Trematoda) Parasites

The dynamics of aggressive behavior of the underyearlings of the rainbow trout Oncorhynchus mykiss infected with metacercariae of the trematodes Diplostomum pseudospathaceum has been studied in an experimental heterogeneous environment for 48 days. The fish competed for the dark area of the bottom by charges, biting, chasing, and frontal and lateral displays. The sharply increased aggressiveness of fish when the parasites became infective (1.0–1.5 months after infection), i.e., capable of infecting the final host (piscivorous birds), manifested itself in an increased frequency of bites (more than 20 times compared to the control) and charges (almost three times) and was accompanied by fast movements, sharp maneuvers, and low ability to compete for shelters. The share of comparatively slow displays and chasing was much smaller. The strategy of D. pseudospathaceum manipulation of fish behavior consists of two stages: (1) protecting the host from predators; (2) increasing the vulnerability of the host. At the first stage, the general level of aggression decreases sharply; at the second, on the contrary, aggressiveness rapidly increases, but the ratio of different categories of aggression changes. The share of categories that make the host more vulnerable to predators increases. High activity and low competitiveness of infected fish contribute to their rapid extermination by predators or moving to another habitat. Such migration of fish can increase the fitness of the parasite, facilitating its dispersal in the water body.

High-resolution app data reveal sustained increases in recreational fishing effort in Europe during and after COVID-19 lockdowns.

It is well recognized that COVID-19 lockdowns impacted human interactions with natural ecosystems. One example is recreational fishing, which, in developed countries, involves approximately 10% of people. Fishing licence sales and observations at angling locations suggest that recreational fishing effort increased substantially during lockdowns. However, the extent and duration of this increase remain largely unknown. We used four years (2018-2021) of high-resolution data from a personal fish-finder device to explore the impact of COVID-19 lockdowns on angling effort in four European countries. We show that relative device use and angling effort increased 1.2-3.8-fold during March-May 2020 and generally remained elevated even at the end of 2021. Fishing during the first lockdown also became more frequent on weekdays. Statistical models explained 50-70% of the variation, suggesting that device use and angling effort were relatively consistent and predictable through space and time. Our study demonstrates that recreational fishing behaviour can change substantially and rapidly in response to societal shifts, with profound ecological, human well-being and economic implications. We also show the potential of angler devices and smartphone applications for high-resolution fishing effort analysis and encourage more extensive science and industry collaborations to take advantage of this information.

Effects of Temperature Variation on Behaviour and Growth Performance of African Catfish Clarias gariepinus

The effect of temperature variation on the behaviour and growth performance of Clarias gariepinus was studied. Temperature has both direct and indirect influence on fisheries and aquaculture. This study was set to evaluate how changes in temperature of the aquatic environment influence the behaviour and growth of Clarias gariepinus as one of the best aquaculture candidates especially in central and western Africa. The fish were subjected to different temperature conditions over a period of eight (8) weeks. Changes in fish behaviour were determined by careful observation of feeding behaviour as well as swimming patterns. Changes in the growth of fish were determined by measuring the weight of the fish and the standard length of the fish accordingly. The outcome of the current study reveals that temperature significantly affects the behaviour and growth performance of Clarias gariepinus. The effect is more significant in the weight than the length of the fish. Temperature values between 20-27 ℃ are more suitable for proper growth and well-being of Clarias gariepinus, any further increase in temperature above 27 ℃ causes a decline in the growth that fish species.

Study of the Response of Environmental Factors of the Coastal Area in Zhoushan Fishery to Typhoon In-fa Based on Remote Sensing

The response of typical environmental factors in Zhoushan Fishery, including sea surface temperature (SST), sea surface salinity (SSS), and chlorophyll a (Chl-a), before and after Typhoon In-fa was analyzed using satellite data and reanalysis data in this study. Additionally, this study simultaneously elucidated the mechanism by which the typhoon affected these factors. The results showed that: (1) the strong vertical mixing caused by In-fa provoked a decrease in SST, while the asymmetric typhoon wind stress and vertical difference in temperature structure before the typhoon caused a more robust cooling of SST on the right side of the In-fa track; (2) despite the strong mixing and inflow of hypersaline seawater increasing SSS, the combined effect of intense rainfall and diluted water inflow caused an overall decrease in SSS after In-fa’s landing; (3) In-fa caused the Chl-a concentration to decrease first and then increase. The high cloudiness and low Chl-a seawater inflow inhibited the phytoplankton growth during the typhoon, while the abundant light, rich surface nutrients under the upwelling effect, and transport of rich land-based substances induced rapid phytoplankton reproduction after the typhoon; and (4) the change in Chl-a concentration, current, temperature, and salinity induced by a typhoon are essential factors that affect fish behavior and community composition in fisheries. This study provides a point of reference to reveal the response of environmental factors to typhoons and their effects on fishery resources in fisheries located on nearshore estuarine shallow waters with intensive islands.

Optimizing zebrafish rearing-Effects of fish density and environmental enrichment.

Despite its popularity in research, there is very little scientifically validated knowledge about the best practices on zebrafish (Danio rerio) husbandry, which has led to several facilities having their own husbandry protocols. This study was performed to expand knowledge on the effects of enrichment and fish density on the welfare of zebrafish, with hopes of providing a scientific basis for future recommendations and legislations. Zebrafish were reared at three different stocking densities, (1, 3 or 6 fish/L), in tanks with or without environmental enrichment. Agonistic behavior was observed twice a week for 9 weeks directly in the housing tanks. Aspects of welfare is known to be reflected in neuroendocrine stress responses. Thus, cortisol secretion in response to lowering the water level was analyzed for each group. In addition, we assessed cortisol secretion in response to confinement and risk-taking behavior (boldness) using the novel tank diving test for individual fish. At termination of the experiment fish were subjected to stress by transfer to a novel environment and brain tissue was sampled for analysis of brain monoaminergic activity. Fish kept at the lowest density (1 fish/L) showed a significantly higher level of aggression than fish kept at 3 or 6 fish/L. Moreover, fish kept at this low density showed significantly higher cortisol secretion on a group level than fish kept at the higher stocking densities, when subjected to lowering of the water level. Keeping fish at 1 fish/L also had effects on brain monoamines, these fish showing higher brain dopamine concentrations but lower dopamine turnover than fish kept at higher densities. Neither stocking density or enrichment had any clear effects on the behavior of individual fish in the novel tank diving test. However, fish kept at high densities showed lower and more variable growth rates than fish kept at 1 fish/L. Taken together these results suggest that zebrafish should not be kept at a density of 1 fish/L. The optimal stocking density is likely to be in the range of 3-6 fish/L.