Control Fish Research Articles

Use of All-Male cyp17a1-Deficient Zebrafish (Danio rerio) for Evaluation of Environmental Estrogens.

Natural and synthetic environmental estrogens (EEs) are widespread and have received extensive attention. Our previous studies demonstrated that depletion of the cytochrome P450 17a1 gene (cyp17a1) leads to all-testis differentiation phenotype in zebrafish and common carp. In the present study, cyp17a1-deficient zebrafish with defective estrogen biosynthesis were used for the evaluation of EEs, as assessed by monitoring vitellogenin (vtg) expression. A rapid and sensitive assessment procedure was established with the 3-day administration of estradiol (E2), followed by examination of the transcriptional expression of vtgs in our cyp17a1-deficient fish. Compared with the control fish, a higher E2-mediated vtg upregulation observed in cyp17a1-deficient zebrafish exposed to 0.1 μg/L E2 is known to be estrogen receptor-dependent and likely due to impaired in vivo estrogen biosynthesis. The more responsive vtg expression in cyp17a1-deficient zebrafish was observed when exposed to 200 and 2000 μg/L bisphenol A (BPA) and perfluoro-1-octanesulfonate (PFOS). The estrogenic potentials of E2, BPA, and PFOS were compared and assessed by the feminization effect on ovarian differentiation in cyp17a1-deficient zebrafish from 18 to 50 days postfertilization, based on which a higher sensitivity of E2 in ovarian differentiation than BPA and PFOS was concluded. Collectively, through the higher sensitivity to EEs and the capacity to distinguish chemicals with different estrogenic potentials exhibited by the all-male cyp17a1-deficient zebrafish with impaired estrogen biosynthesis, we demonstrated that they can be used as an excellent in vivo model for the evaluation of EEs. Environ Toxicol Chem 2024;43:1062-1074. © 2024 SETAC.

Repeated copper sulfate treatments have no effect on growth and survival of juvenile Walleye

AbstractObjectiveAn experiment was conducted to evaluate the effects of repeated copper sulfate (CuSO4) treatments on the growth and survival of juvenile Walleye Sander vitreus.MethodsCulture tanks were treated with 0 or 0.76 mg/L CuSO4 every other day for five exposures, then were not treated for 14 consecutive days; this regimen was repeated for a total of 10 exposures over the course of 50 days. Copper sulfate treatments had a half‐life of about 60 min. The study was conducted in flow‐through well water at ≈1.5 L/m and 23.8°C.ResultThe resulting survival data for CuSO4 treated and nontreated fish was 96% and 85% survival, respectively, and not statically different. There was no difference in weight, with treated weighing 25.3 g compared to 25.2 g for nontreated control fish. Both groups had weight increases of over 400% during the study. Neither group differed in length, with treated fish reaching a mean length of 14.6 cm and nontreated reaching a mean length of 14.5 cm.ConclusionThe results indicate that repeated CuSO4 treatments had no effect on Walleye growth or survival.

Pesticide-induced alterations in zebrafish (Danio rerio) behavior, histology, DNA damage and mRNA expression: An integrated approach

To assess the impact of glyphosate and 2,4-D herbicides, as well as the insecticide imidacloprid, both individually and in combination, the gills of adult zebrafish were used due to their intimate interaction with chemicals diluted in water. Bioassays were performed exposing the animals to the different pesticides and their mixture for 96 h. The behavior of the fish was analyzed, a histological examination of the gills was carried out, and the genotoxic effects were also analyzed by means of the comet assay (CA) and the change in the expression profiles of genes involved in the pathways of the oxidative stress and cellular apoptosis. The length traveled and the average speed of the control fish, compared to those exposed to the pesticides and mainly those exposed to the mixture, were significantly greater. All the groups exposed individually exhibited a decrease in thigmotaxis time, indicating a reduction in the behavior of protecting themselves from predators. Histological analysis revealed significant differences in the structures of the gill tissues. The quantification of the histological lesions showed mild lesions in the fish exposed to imidacloprid, moderate to severe lesions for glyphosate, and severe lesions in the case of 2,4-D and the mixture of pesticides. The CA revealed the sensitivity of gill cells to DNA damage following exposure to glyphosate, 2,4-D, imidacloprid and the mixture. Finally, both genes involved in the oxidative stress pathway and those related to the cell apoptosis pathway were overexpressed, while the ogg1 gene, involved in DNA repair, was downregulated.

Alteration of shoaling behavior and dysbiosis in the gut of medaka (Oryzias latipes) exposed to 2-μm polystyrene microplastics

There is global concern that microplastics may harm aquatic life. Here, we examined the effects of fine polystyrene microplastics (PS-MPs, 2-μm diameter, 0.1 mg/L, 2.5 × 107 particles/L) on the behavior and the microbiome (linked to brain–gut interaction) of a fish model using medaka, Oryzias latipes. We found that shoaling behavior was reduced in PS-MP-exposed medaka compared with control fish during the exposure period, but it recovered during a depuration period. There was no difference in swimming speed between the PS-MP-exposed and control groups during the exposure period. Analysis of the dominant bacterial population (those comprising ≥1% of the total bacterial population) in the gut of fish showed that exposure to PS-MPs tended to increase the relative abundance of the phylum Fusobacteria and the genus Vibrio. Furthermore, structural-equation modeling of gut bacteria on the basis of machine-learning data estimated strong relationship involved in the reduction of the functional bacterial species of minority (<1% of the total bacterial population) such as the genera Muribaculum (an undefined role), Aquaspirillum (a candidate for nitrate metabolism and magnetotactics), and Clostridium and Phascolarctobacterium (potential producers of short-chain fatty acids, influencing behavior by affecting levels of neurotransmitters) as a group of gut bacteria in association with PS-MP exposure. Our results suggest that fish exposure to fine microplastics may cause dysbiosis and ultimately cause social behavior disorders linked to brain–gut interactions. This effect could be connected to reduction of fish fitness in the ecosystem and reduced fish survival.

Tilapia lake virus infection disrupts the gut microbiota of red hybrid tilapia (Oreochromis spp.)

Viral infections have the potential to damage fish intestines and disrupt the composition and diversity of the bacterial populations. In this study, we investigated the gut microbiota profiles of 23 red hybrid tilapia (10 ± 3 g) infected with Tilapia lake virus (TiLV) via two different methods. For the intraperitoneal (IP)-injection, 50 μl of TiLV at a concentration of 105 TCID50/ml was administered into the fish's coelomic cavity. In the cohabitation challenge method, infection was achieved by injecting the virus into the coelomic cavity of the inducer fish and allow them to cohabited with cohabitation fish at a ratio of 1:3. The cohabitation infected fish had a cumulative mortality rate of 49%, while the IP-injection group had 81.5%, which was accompanied by clinical signs, severe histopathological changes in the intestines and high viral loads in the intestines over the infection period at 6, 12 and 21 days post challenge (dpc). Most importantly, an analysis of the bacterial populations based on the alpha and beta diversity patterns revealed distinct alterations in the intestines of the fish infected via IP injection and cohabitation and the control fish. Specifically, our findings highlighted a reduction in Cetobacterium (phylum Fusobacterium) and an increase in Brevinema (phylum Spirochaetes) in the infected fish at 6 and 12 dpc. Indeed, the elevation of Brevinema population is associated with a higher mortality rate within the IP-injection compared to the cohabitation group. Remarkably, the fish that survived TiLV infection at 21 dpc showed a higher abundance of Bacillus (phylum Firmicutes), which was in contrast to that at earlier time points (6 and 12 dpc). While Brevinema has been recognised as a potentially opportunistic pathogen in fish, different strains of Bacillus are commonly used as probiotics to promote fish health and enhance disease resistance. Our findings thus provide valuable insights into the distinct shifts occurring within fish gut microbiota during TiLV infection and suggest potential implications for improving gut health and resistance to viral infections in tilapia. Taken together, our study establishes that TiLV infection triggers significant changes in the diversity and composition of the intestinal microbiota in red hybrid tilapia.

Evaluation of coriander seed powder supplementation on body composition, growth performance, hematology, and serum biochemical indices in common carp (Cyprinus carpio) fingerlings.

This study aimed to investigate the role of coriander seed powder (Coriandrum sativum) on growth indices, feed utilization, body composition, and haemato-biochemical parameters in common carp (Cyprinus carpio) fingerlings over 84 days. One hundred and forty-four common carp (25.24±0.05 g) were assigned into four groups fed with different diets, namely 0 (basal diet), 1%, 2%, and 4% of coriander seed powder (CSP). In the current study, C. carpio fed with dietary CSP revealed significant improvement in weight gain, final weight, specific growth rate, total feed intake, feed conversion efficiency, feed conversion ratio, protein intake, and protein efficiency ratio, in comparison to control fish fed after 84 days (P>0.05). It was also found that fish fed with 1%CSP-supplemented dietary had the best growth performance and feed utilization. The crude protein of fish fed with CSP dietary treatments increased, and significant differences were only found in the fish fed with 1%CSP diet, in comparison to the control group. The CSP supplementation groups showed significant increases in hemoglobin, hematocrit, albumin, total protein, and globulin compared to the control group. Nevertheless, differential white blood cells, mean corpuscular hemoglobin concentration, cholesterols, and triglycerides were significantly reduced in the CSP dietary group in comparison to the control group. It was also found that CSP dietary treatment significantly increased lipase and amylase in comparison to the control group (P>0.05). However, the highest lipase and amylase levels were obtained at 1%CSP and 2%CSP dietary treatment groups, compared to the control basal diet. Based on the results, CSP supplementation could improve the overall health status and growth performance of common carp fingerlings.

Estrogen Signaling Inhibits the Expression of anti-Müllerian hormone (amh) and gonadal-soma-derived factor (gsdf) during the Critical Time of Sexual Fate Determination in Zebrafish.

The mechanism of fish gonadal sex differentiation is complex and regulated by multiple factors. It has been widely known that proper steroidogenesis in Leydig cells and sex-related genes in Sertoli cells play important roles in gonadal sex differentiation. In teleosts, the precise interaction of these signals during the sexual fate determination remains elusive, especially their effect on the bi-potential gonad during the critical stage of sexual fate determination. Recently, all-testis phenotypes have been observed in the cyp17a1-deficient zebrafish and common carp, as well as in cyp19a1a-deficient zebrafish. By mating cyp17a1-deficient fish with transgenic zebrafish Tg(piwil1:EGFP-nanos3UTR), germ cells in the gonads were labelled with enhanced green fluorescent protein (EGFP). We classified the cyp17a1-deficient zebrafish and their control siblings into primordial germ cell (PGC)-rich and -less groups according to the fluorescence area of the EGFP labelling. Intriguingly, the EGFP-labelled bi-potential gonads in cyp17a1+/+ fish from the PGC-rich group were significantly larger than those of the cyp17a1-/- fish at 23 days post-fertilization (dpf). Based on the transcriptome analysis, we observed that the cyp17a1-deficient fish of the PGC-rich group displayed a significantly upregulated expression of amh and gsdf compared to that of control fish. Likewise, the upregulated expressions of amh and gsdf were observed in cyp19a1a-deficient fish as examined at 23 dpf. This upregulation of amh and gsdf could be repressed by treatment with an exogenous supplement of estradiol. Moreover, tamoxifen, an effective antagonist of both estrogen receptor α and β (ERα and Erβ), upregulates the expression of amh and gsdf in wild-type (WT) fish. Using the cyp17a1- and cyp19a1a-deficient zebrafish, we provide evidence to show that the upregulated expression of amh and gsdf due to the compromised estrogen signaling probably determines their sexual fate towards testis differentiation. Collectively, our data suggest that estrogen signaling inhibits the expression of amh and gsdf during the critical time of sexual fate determination, which may broaden the scope of sex steroid hormones in regulating gonadal sex differentiation in fish.

Experimental Infection and the Effects of Temperature on the Pathogenicity of the Infectious Spleen and Kidney Necrosis Virus in Juvenile Nile Tilapia (Oreochromis niloticus)

The infectious spleen and kidney necrosis virus (ISKNV) is one of the most important emerging viral pathogens for Nile tilapia (Oreochromis niloticus) farming. While prevalent worldwide, it has recently been detected in Brazil. However, despite the importance of the virus and the affected fish species, there are no scientific data on the effects of water temperature on disease pathogenesis in Nile tilapia. In the present study, we conducted two trials using juvenile Nile tilapia over a 15-day period. In trial 1, an experimental infection model was developed based on the intraperitoneal inoculation of active viral homogenates (4.3 × 104 virus fish−1), while control fish were similarly inoculated with inactivated viral homogenates. In trial 2, the fish were maintained at different water temperatures (26, 28, 30, 32, and 34 °C) and then infected with ISKNV. For virus detection, kidney and spleen samples were collected and analyzed by qPCR. Our results show that the disease was successfully reproduced in experimental conditions with active homogenates, with the first signs of the disease appearing on the third day after infection. In addition, a significant reduction in mortality was observed in the groups maintained at higher temperatures (&gt;30 °C). This suggests that a treatment of the disease with non-lethal hyperthermia can be used to control the symptoms and mortality of ISKNV-infected Nile tilapia juveniles.

Survival and swimming performance in small-sized South European Cypriniformes tagged with passive integrated transponders

A fundamental assumption in animal telemetry is that the behavior and performance of tagged animals do not substantially deviate from that of untagged animals. For fish, swimming behavior is fundamental for every part of a fish post-hatch life, influencing predator-prey interactions, movement ecology, and habitat choice. Here, we study the effects of PIT-tagging on survival and a range of swimming behaviors for South European nase (Protochondrostoma genei) and brook barbel (Barbus caninus), two small-sized, stream-dwelling cypriniforms native to the Italian peninsula. Effects on volitional swimming activity (sustained swimming) and maximum swimming speed (escape response; burst swimming) were tested in arena trials. Tagging effects on the prolonged swimming performance were tested in South European nase in an increasing velocity time-to-fatigue test, while a barrier passage test was designed to further investigate tagging effects in brook barbel. Both species displayed very high survival (95–100%), with no difference between tagged and control fish. No fish lost a tag during the 64 days of the study, and no tagging effect on swimming activity, prolonged swimming performance, barrier passage rate, or escape response was detected. Our results indicate that PIT-telemetry is a suitable tool to study the tested fish species.

The Impact of Marine Resource-Free Diets on Quality Attributes of Atlantic Salmon

The influence of feeding Atlantic salmon for 90 days on diets that excluded fishmeal (FM) and fish oil (FO) was examined for influence on various quality traits. In addition, the effect of adding krill meal (KM; 0%, 2.5%, and 5%), as a putative feed palatant was also examined. Total replacement of FM/FO had a limited effect on production characteristics, affecting percentage yields of headed and gutted control fish and their standard length (p &lt; 0.05). Variances between dietary groups were observed for pigmentation, and plant protein-based KM-free-fed fish returned deeper hues across their belly, NQC (Norwegian Quality Cut), and back portions (p &lt; 0.03). No differences were measured for relative fin condition. δ13C and δ15N concentrations were lower and higher, respectively (p &lt; 0.05) for fish fed the FM/FO-based diet. δ13C:δ15N likewise differed between treatments with FM/FO-fed salmon expressing higher ratios. Fillet mechanical characteristics varied with fish fed on animal protein-based diets, without KM expressing higher springiness and resilience (p &lt; 0.05). Fish fed plant-based diets were generally preferred by younger taste testers. The results from this trial illustrate that FM/FO can be completely removed from salmon diets without problematic effects on quality and palatability attributes.

Repeated boat noise exposure damages inner ear sensory hair cells and decreases hearing sensitivity in Atlantic croaker (Micropogonias undulatus).

Anthropogenic noise is becoming a major underwater pollutant because of rapidly increasing boat traffic worldwide. But its impact on aquatic organisms remains largely unknown. Previous studies have focused mainly on high-frequency and impulsive noises (i.e. sonar); however, boat noise is more pervasive, continuous, and its highest intensity and component frequencies overlap the auditory bandwidth of most fishes. We assessed the impacts of boat noise on saccular sensory hair cell density and hearing thresholds of a soniferous species, Atlantic croaker (Micropogonias undulatus). In two laboratory experiments, individuals were subjected to simulated boat noise: a single 15-min exposure and 3days of intermittent noise (simulating passing vessels). Immediately after both experiments, fish were either (1) tested for hearing sensitivity with auditory evoked potential (AEP) tests or (2) euthanized for fluorescent phalloidin and TUNEL labeling for hair cell density counts. Relative to controls, no differences were observed in auditory thresholds nor hair cell density between individuals subjected to a single 15-min noise exposure. However, fish from the 3-day experiment showed decreased sensory hair cell density, increased apoptotic cells, and higher hearing thresholds than control fish at 300, 800 and 1000 Hz. Our results demonstrate that impacts from boat noise depend upon the duration and frequency of exposure. For a species reliant on vocalization for communication, these impacts may hinder spawning success, increase predation risks and significantly alter the ecosystem.

Coinfection of channel catfish (Ictalurus punctatus) with virulent Aeromonas hydrophila and Flavobacterium covae exacerbates mortality.

Flavobacterium covae and virulent Aeromonas hydrophila are prevalent bacterial pathogens within the US catfish industry that can cause high mortality in production ponds. An assessment of invivo bacterial coinfection with virulent A. hydrophila (ML09-119) and F. covae (ALG-00-530) was conducted in juvenile channel catfish (Ictalurus punctatus). Catfish were divided into seven treatments: (1) mock control; (2) and (3) high and low doses of virulent A. hydrophila; (4) and (5) high and low doses of F. covae; (6) and (7) simultaneous challenge with high and low doses of virulent A. hydrophila and F. covae. In addition to the mortality assessment, anterior kidney and spleen were collected to evaluate immune gene expression, as well as quantify bacterial load by qPCR. At 96 h post-challenge (hpc), the high dose of virulent A. hydrophila infection (immersed in 2.3 × 107 CFU mL-1 ) resulted in cumulative percent mortality (CPM) of 28.3 ± 9.5%, while the high dose of F. covae (immersed in 5.2 × 106 CFU mL-1 ) yielded CPM of 23.3 ± 12.9%. When these pathogens were delivered in combination, CPM significantly increased for both the high- (98.3 ± 1.36%) and low-dose combinations (76.7 ± 17.05%) (p < .001). Lysozyme activity was found to be different at 24 and 48 hpc, with the high-dose vAh group demonstrating greater levels than unexposed control fish at each time point. Three proinflammatory cytokines (tnfα, il8, il1b) demonstrated increased expression levels at 48 hpc. These results demonstrate the additive effects on mortality when these two pathogens are combined. The synthesis of these mortality and health metrics advances our understanding of coinfections of these two important catfish pathogens and will aid fish health diagnosticians and channel catfish producers in developing therapeutants and prevention methods to control bacterial coinfections.

Evaluation of three inactive vaccines against Veronaea botryosa infection in white sturgeon (Acipenser transmontanus)

Veronaea botryosa is the etiological agent of a systemic phaeohyphomycosis known as “fluid belly” in white sturgeon (Acipenser transmontanus). Fluid belly is a critical disease affecting sturgeon aquaculture and the caviar industry for which there are no commercially available vaccines or approved antifungal treatments to manage outbreaks. The primary aim of this study was to investigate the effect of a V. botryosa [conidia], a V. botryosa [mold], and a Saccharomyces cerevisiae [yeast] formalin-killed vaccine on sturgeon immune responses to fungal challenge. Immunization consisted of an initial intracoelomic injection with one of the three treatment preparations, followed by a vaccine booster four weeks later by the same route and dose. Experimental challenge by intramuscular injection with a virulent V. botryosa conidia suspension followed after another four weeks. Non-challenged control fish received injections of PBS. The inactivated vaccines proved safe for white sturgeon fingerlings. Sturgeon immunized with either V. botryosa [mold] or S. cerevisiae [yeast] exhibited a significantly different pro-inflammatory response upon challenge with V. botryosa compared to non-immunized fish. Challenged fish developed clinical signs similar to those reported during natural outbreaks of fluid belly. Positive control treatments (those not immunized but challenged with V. botryosa) experienced the highest mortality; however, survival curves were similar amongst all treatments (p < 0.05). Furthermore, the S. cerevisiae [yeast] vaccine resulted in comparatively lower fungal persistence and fewer lesions following histological analysis. Further efforts evaluating the potential of Saccharomyces spp. as a vaccine candidate against fluid belly are warranted.

Assessing the impact of dietary polystyrene nanoplastics on growth performance, immunological parameters, and antioxidant defense in zebrafish (Danio rerio)

AbstractThis trial was performed in order to investigate the response of zebrafish (Danio rerio) to dietary exposure to polystyrene nanoplastics (PS‐NPs) under laboratory conditions on fish growth and health. Healthy zebrafish (n=240) were divided into 12 tanks and fed with diets including 0 (T0), 100 (T1), 500 (T2), and 1000 (T3) mg kg−1 synthesized polystyrenes nanoplastics (PS‐NPs) for 30 days. At the end of trial, fish fed the PS‐NPs supplementation showed weight gain percentages of 79.45%, 70.35%, and 61.88% for T1, T2, and T3 groups, respectively, compared with 87.39% in the control fish. The SOD, GPX and MDA activities and cortisol levels increased by 47%, 32% and 35% and 46%, respectively, especially at high‐dose administration (p &lt; 0.05). The expression of GPX (T2‐81% and T3‐82%) and SOD (T2‐101% and T3‐187%) were remarkably upregulated in T2 and T3 groups. Moreover, the relative gene expression of HSP70, interleukin‐1 (IL1), Interferon γ (IFN‐γ) and tumor necrosis factor‐α (TNF‐α) increased by 178%, 202%, 154% and 307%, respectively, especially at high‐dose administration (p &lt; 0.05). The results of the present study demonstrated that exposure to PS‐NPs especially at high concentrations (500 and 1000 mg kg−1 of diet) negatively influenced growth, health status‐, antioxidant‐, and immunity‐related gene expression responses of zebrafish.

Effects of temperature acclimation on the upper thermal tolerance of two Arctic fishes.

The thermally dynamic nearshore Beaufort Sea, Alaska, is experiencing climate change-driven temperature increases. Measuring thermal tolerance of broad whitefish (Coregonus nasus) and saffron cod (Eleginus gracilis), both important species in the Arctic ecosystem, will enhance understanding of species-specific thermal tolerances. The objectives of this study were to determine the extent that acclimating broad whitefish and saffron cod to 5°C and 15°C changed their critical thermal maximum (CTmax) and HSP70 protein and mRNA expression in brain, muscle and liver tissues. After acclimation to 5°C and 15°C, the species were exposed to a thermal ramping rate of 3.4°C · h-1 before quantifying the CTmax and HSP70 protein and transcript concentrations. Broad whitefish and saffron cod acclimated to 15°C had a significantly higher mean CTmax (27.3°C and 25.9°C, respectively) than 5°C-acclimated fish (23.7°C and 23.2°C, respectively), which is consistent with trends in CTmax between higher and lower acclimation temperatures. There were species-specific differences in thermal tolerance with 15°C-acclimated broad whitefish having higher CTmax and HSP70 protein concentrations in liver and muscle tissues than saffron cod at both acclimation temperatures. Tissue-specific differences were quantified, with brain and muscle tissues having the highest and lowest HSP70 protein concentrations, respectively, for both species and acclimation temperatures. The differences in broad whitefish CTmax between the two acclimation temperatures could be explained with brain and liver tissues from 15°C acclimation having higher HSP70a-201 and HSP70b-201 transcript concentrations than control fish that remained in lab-acclimation conditions of 8°C. The shift in CTmax and HSP70 protein and paralogous transcripts demonstrate the physiological plasticity that both species possess in responding to two different acclimation temperatures. This response is imperative to understand as aquatic temperatures continue to elevate.

Immunological effects of vitamin c and zinc on tilapia (Orechromis niloticus) exposed to cold water stress.

This study investigates the immunological and growth effects of Vitamin C and Zinc supplementation on Nile tilapia (Oreochromis niloticus) subjected to cold water stress. Nile tilapia fingerlings were housed in eight 20-gallon tanks at Purdue University, acclimated to 26 ± 2°C water conditions before the experiment. The tilapia was divided into groups with varying water temperatures and feed supplements: control fish in warm water, and experimental groups in cold water with increased levels of Vitamin C and Zinc. Stress was induced by lowering the water temperature to 15 ± 2°C in four tanks, while the remaining tanks were kept at the optimal growth temperature. Results demonstrated that Vitamin C and Zinc supplementation significantly enhanced immune response and muscle regeneration in cold-stressed tilapia, allowing them to achieve growth rates comparable to those of control fish in optimal warm water conditions. These findings highlight the potential benefits of combined Vitamin C and Zinc supplementation in improving the immune response and growth performance of tilapia under suboptimal temperature conditions.

Naphthenic acid fraction compounds, produced by the extraction of bitumen from oil sands, alter survival and behaviour of juvenile yellow perch (Perca flavescens)

We evaluated whether naphthenic acid fraction compounds (NAFCs) extracted from oil sand tailings adversely affect fish survival and behaviour. Following a before–after-control-impact design, we housed wild-caught juvenile yellow perch ( Perca flavescens) in outdoor mesocosms to assess survival and behaviour under baseline conditions, then exposed fish to one of three treatments: negative control, 2 mg/L NAFC, or 15 mg/L NAFC. We performed behavioural assays (no-stimulus activity, food stimulus, and predator stimulus using a model bird) and assessed a comprehensive suite of endpoints (equilibrium losses, activity, shoaling, burst swimming, freezing, and space use). We found that exposure to 15 mg/L NAFCs substantially reduced fish survival and impaired fish equilibrium in all three behavioural tests. Furthermore, exposure to NAFCs impaired anti-predator behaviour: while the activity of control fish increased by two-fold in response to a predator stimulus, fish exposed to 2 or 15 mg/L NAFC did not change their activity levels after stimulation. No significant changes were observed in other behavioural endpoints. Overall, our findings suggest that a week-long exposure to NAFCs at concentrations commonly found in tailings ponds, constructed wetlands, and other mining-impacted waters may affect multiple facets of fish behaviour that could ultimately lead to reduced fitness in fish populations.

Evaluation of &lt;em&gt;Chromolaena odorata&lt;/em&gt; as Growth Promoter in the African Catfish (&lt;em&gt;Clarias gariepinus&lt;/em&gt;, Burchell 1822)

The effect of different concentrations of Chromolaena odorata (Siam weed) supplementation in fish feed on Clarias gariepinus fingerling growth characteristics was examined. Fish were randomly assigned to one of the four experimental groups: 0.0 percent (controls), 0.5 percent, 1.0 percent, and 3.0 percent concentrations of Chromolaena odorata in feed. Fish was fed at 5 percent body weight (g) per day for 70 days. Results showed that fish-fed the treatment diet had no significant effect on weight gain. The final body lengths (cm) of all treated groups were marginally (P &gt; 0.05) different from the control group after 70 days. When the growth parameters were considered, the fish fed the diet containing 1.0 percent Chromolaena odorata had the best growth response (2.4±0.04g) while the fish fed the control diet had the slowest growth (1.2±0.13g). In comparison with the control fish fed the diet containing 1.0 percent Chromolaena odorata had the best feed conversion ratio (FCR), specific growth rate (SGR), and condition factor (K) This study showed that the inclusion of Chromolaena odorata in fish food at 0.5 – 3.0 percent level did not significantly increase the weight and length of catfish.

Fluoxetine may interfere with learning in fish

Our study aimed to test whether fluoxetine impairs learning in fish and whether this potential impairment is reversible. Learning efficiency, with no aversive stimuli, of the Carassius carassius was analysed under different pharmaceutical conditions: (i) fish cultured without antidepressant (control), (ii) fish exposed to fluoxetine for 21 days (fluoxetine), and (iii) fish exposed to fluoxetine for 21 days and then cultured without fluoxetine for another 21 days (recovery). We exposed animals to environmental concentrations (360 ng L−1) of antidepressant. The learning rate was measured by timing how long it took the individual fish to find food and start feeding, six days in a row. The control and recovery fish took significantly less time to start eating over the six days. Control fish start eating 14 times faster than the fluoxetine fish. Fluoxetine can significantly affect learning and 21-day recovery period is not enough to fully restore the original learning abilities.

Tissue Lipid Profiles of Rainbow Trout, Oncorhynchus mykiss, Cultivated under Environmental Variables on a Diet Supplemented with Dihydroquercetin and Arabinogalactan.

Reared rainbow trout are vulnerable to environmental stressors, in particular seasonal water warming, which affects fish welfare and growth and induces a temperature response, which involves modifications in tissue lipid profiles. Dietary supplements of plant origin, including the studied mix of a flavonoid, dihydroquercetin and a polysaccharide, arabinogalactan (25 and 50 mg per 1 kg of feed, respectively), extracted from larch wood waste, were shown to facilitate stress tolerance in fish and also to be beneficial for the safety of natural ecosystems and the sustainability of aquaculture production. This four-month feeding trial aimed to determine the effects of the supplement on liver and muscle lipid accumulation and the composition in rainbow trout reared under environmental variables. During periods of environmental optimum for trout, a consistent increase in energy lipid stores, particularly triacylglycerols (2.18 vs. 1.49-fold over a growing season), and an overall increase in lipid saturation due to lower levels of PUFAs, such as eicosapentaenoic (20:5n-3), docosahexaenoic (22:6n-3) and arachidonic (20:4n-6) acids, were observed in both control and supplement-fed fish, respectively. However, in fish stressed by an increase in ambient temperature, dietary supplementation with dihydroquercetin and arabinogalactan reduced mortality (3.65 in control vs. 2.88% in supplement-fed fish, p < 0.05) and alleviated the high-temperature-induced inhibition of lipid accumulation. It also stabilised the membrane phospholipid ratio and moderated the fatty acid composition of fish muscle and liver, resulting in higher levels of n-3 PUFAs and their precursors. Thus, the natural compounds tested are beneficial in accelerating fish tolerance to environmental stressors, reducing mortality and thermal response, and moderately improving fillet quality attributes by increasing the protein/lipid ratio and the abundance of fatty acids essential for human nutrition.