The alarm reaction of coho salmon parr is impaired by the carbamate fungicide IPBC

Exposure to carbamate fungicide iodocarb does not affect reproductive behavior or milt volumes in precocious male brown trout (Salmo trutta L.) parr

Previous studies with olfactory-disturbing pesticides resulted after exposure in disturbed behavior and physiology in fish. In the present experiment, reproductive behavior and milt volumes of precocious brown trout (Salmo trutta L.) male parr were studied in a large stream aquarium after exposure to the olfactory-disturbing fungicide 15 μg l^-1 IPBC (iodocarb; 3-iodo-2-propynyl butyl carbamate) for 96 h. The statistical analyses did not reveal any significant differences for time attending females between controls and IPBC-exposed males. Furthermore, there were no significant differences in milt volumes. However, when taking all fish into consideration, there were significant differences in milt volumes between parr that had been attending females and those had not been attending females. Controls that had attended females had significantly higher milt volumes than controls or IPBC-exposed males that had not attended females. Taking all control and IPBC parr into consideration, there was a statistically significant positive correlation between time attended females and volume of milt and gonadosomatic index (GSI), respectively. In summary, 15 μg l^-1 IPBC did not have any significant effects on mature male parr reproductive behavior and milt volumes.

Zebrafish Models in Neural and Behavioral Toxicology across the Life Stages

The industry is increasingly relying on fish for toxicity assessment. However, current guidelines for toxicity assessment focus on teratogenicity and mortality. From an ecotoxicological point of view, however, these endpoints may not reflect the “full picture” of possible deleterious effects that can nonetheless result in decreased fitness and/or inability to adapt to a changing environment, affecting whole populations. Therefore, assessing sublethal effects add relevant data covering different aspects of toxicity at different levels of analysis. The impacts of toxicants on neurobehavioral function have the potential to affect many different life-history traits, and are easier to assess in the laboratory than in the wild. We propose that carefully-controlled laboratory experiments on different behavioral domains—including anxiety, aggression, and exploration—can increase our understanding of the ecotoxicological impacts of contaminants, since these domains are related to traits such as defense, sociality, and reproduction, directly impacting life-history traits. The effects of selected contaminants on these tests are reviewed, focusing on larval and adult zebrafish, showing that these behavioral domains are highly sensitive to small concentrations of these substances. These strategies suggest a way forward on ecotoxicological research using fish.

Do you smell the danger? Effects of three commonly used pesticides on the olfactory-mediated antipredator response of zebrafish (Danio rerio)

Fish are warned about the presence of predators via an alarm cue released from the skin of injured conspecifics. The detection of this odor inherently initiates an antipredator response, which increases the chance of survival for the individual. In the present study, we assessed the effect of three commonly used pesticides on the antipredator response of zebrafish (Danio rerio). For this, we analyzed the behavioral response of zebrafish to a conspecific skin extract following 24 h of exposure to the respective contaminants. Results demonstrate that fish exposed to 20 μg/L of the organophosphate insecticide chlorpyrifos significantly reduced bottom-dwelling and freezing behavior, suggesting an impairment of the antipredator response. For the urea-herbicide linuron and the pyrethroid insecticide permethrin, no statistically significant effects could be detected. However, linuron-exposed fish appeared to respond in an altered manner to the skin extract; some individuals failed to perform the inherent behaviors such as erratic movements and instead merely increased their velocity. Furthermore, we determined whether zebrafish would avoid the pesticides in a choice maze. While fish avoided permethrin, they behaved indifferently to chlorpyrifos and linuron. The study demonstrates that pesticides may alter the olfactory-mediated antipredator response of zebrafish in distinct ways, revealing that particularly fish exposed to chlorpyrifos may be more prone to predation.

The interactive effect of copper(II) and conspecific alarm substances on behavioural responses of zebrafish (Danio rerio)

Environmental contaminants such as metal ions can have detrimental effects on aquatic organisms at the molecular, organismal and population levels. In the present work, we examined the interactive effect of Cu(II) and conspecific alarm substance on zebrafish behavioural responses utilizing the novel tank diving assay. To this end, 3 novel tank diving tests (on day 0, 3 and 10 of the experimental phase) were conducted on zebrafish in 4 experimental groups: (1) control: no Cu(II) and no alarm substance, (2) Cu(II) only: exposed to 0.78 μM Cu(II) (25 % of the 240 h LC50) in the home tank for 10 days, (3) alarm substance only: exposed to alarm substance for 6 min concomitant with behavioural testing, and (4) Cu(II) + alarm substance: exposed to 0.78 μM Cu(II) in the home tank for 10 days and treated with alarm substance for 6 min during the behavioural testing. Results showed robust habituation response of zebrafish. Exposure to Cu(II) did not affect the behavioural phenotypes of zebrafish in the novel tank diving test or habituation responses. Alarm substance treatment evoked strong anxiety-like behaviour. Finally, zebrafish in the Cu(II) + alarm substance group lost their sensitivity to alarm substance in repeated novel tank assays throughout the concomitant Cu(II) exposure; this observation is tentatively ascribed to Cu(II)-induced olfactory impairment.

Behavioural responses of Pacific salmon to chemical disturbance cues during the spawning migration

Many fish that are exposed to a threat release disturbance cues, which are chemicals that alert conspecifics to the presence of the threat. The release of disturbance cues has been well demonstrated in various species of laboratory-reared fish. Migratory fish species often exhibit increased cortisol levels and are exposed to numerous stressors during their migrations, which could trigger the release of disturbance cues. We tested the responses of wild migrating sockeye salmon (Oncorhynchus nerka) and pink salmon (O. gorbuscha) to the odours of disturbed and undisturbed conspecifics to determine whether these fish release disturbance cues following exposure to a simulated stressor. Furthermore, we tested the responses of sockeye salmon to water-borne cortisol, following evidence from past studies that this chemical is excreted through the gills of stressed fish, and speculation that endogenous correlates of stress might function as disturbance cues. We found that sockeye salmon avoid the odour of disturbed conspecifics, whereas pink salmon do not. Avoidance occurred in both female and male sockeye salmon, and was associated with an increase in plasma cortisol levels in females, but not in males. We also found no behavioural response to water-borne cortisol, which suggests this chemical does not act as an exogenous disturbance cue in sockeye salmon. Avoidance of disturbed conspecifics could limit exposure to risks during the sockeye salmon spawning migration, but could also delay the rate of migration and thereby accrue reproductive costs.

Chemical avoidance responses of fishes

The hydrosphere is a repository for all of our waste and mistakes, be they sewage, garbage, process-affected waters, runoff, and gases. For fish living in environments receiving undesirable inputs, moving away seems an obvious way to avoid harm. While this should occur, there are numerous examples where it will not. The inability to avoid harmful environments may lead to sensory impairments that in turn limit the ability to avoid other dangers or locate benefits. For avoidance to occur, the danger must first be perceived, which may not happen if the fish is 'blinded' in some capacity. Second, the danger must be recognized for what it is, which may also not happen if the fish is cognitively confused or impaired. Third, it is possible that the fish may not be able to leave the area, or worse, learns to prefer a toxic environment. Concerning generating regulations around avoidance, there are two possibilities: that an avoidance threshold be used to set guidelines for effluent release with the intention of driving fishes away; the second is to set a contaminant concentration that would not affect the avoidance or attraction responses to other cues. With the complexities of the modern world in which we release diverse pollutants, from light to municipal effluents full of 1000s of chemicals, to the diversity present in ecosystems, it is impossible to have avoidance data on every stimulus-species combination. Nevertheless, we may be able to use existing avoidance response data to predict the likelihood of avoidance of untested stimuli. Where we cannot, this review includes a framework that can be used to direct new research. This review is intended to collate existing avoidance response data, provide a framework for making decisions in the absence of data, and suggest studies that would facilitate the prediction of risk to fish health in environments receiving intentional and unintentional human-based chemical inputs.

Skin extract from Rhamdia quelen(Siluriformes: Heptapteridae) does not promote stress in conspecifics

Chemical communication is widely used in aquatic environments, where visual or auditory signals may not be always effective. Fish of the superorder Ostariophysi are known to display epidermal cells (club cells) that produce and store alarm substances, which are released to the water when the skin is damaged. Responses to alarm substances range widely, between active searches for refuge to a complete stop in any locomotor activity. In this study a large number of binucleated club cells (average density of 11 cells /5m2) were histologically observed in the skin of the catfish Rhamdia quelen (known as jundia). Skin extract (2, 5, and 10% w/v) applied for 15 minutes to conspecifics elicited increase in swimming activity and in the area visited by the fish inside the tank. However, exposure to the epithelial alarm cue did not evoke any stress response: plasma osmolality, ions (sodium, chloride, magnesium, and potassium), glucose and cortisol remained unchanged. In conclusion, the conspecific alarm cue of the jundia induces behavioral responses but not an acute stress response upon short-term exposure, compatible with its role in fostering physical integrity without representing major stress activation. Considering that in the natural environment such stimuli must quickly disappear due to dilution and that rapid protection responses may be necessary upon the possibility of an approaching predator, a faster mechanism to assure survival may come into play, such as sympathetic nervous system activation.

Carbaryl exposure and recovery modify the interrenal and thyroidal activities and the mitochondria-rich cell function in the climbing perch Anabas testudineus Bloch

We examined the effects of carbaryl (1-naphthyl methylcarbamate; sevin), a carbamate pesticide, on interrenal and thyroid activities and mitochondrial rich (MR) cell function in climbing perch to understand the physiological basis of toxicity acclimation in this fish to the chemical stressor. Carbaryl exposure (5-20 mg L(-1)) for 48 h increased cortisol and glucose, but decreased the T(3) level without affecting T(4) concentration in the plasma. These responses of the carbaryl-exposed fish were nullified and a rise in plasma T(4) occurred in these fish when they were kept for 96 h recovery in clean water. A tight plasma mineral control was indicated in the carbaryl-exposed fish as reflected by the unchanged plasma Na, K, Ca and inorganic phosphate levels. The ouabain-sensitive Na(+), K(+)-ATPase activity showed an increase in the gills but the intestinal and renal tissues showed little response to carbaryl treatment. However, substantial increases in the intestinal and renal Na(+), K(+)-ATPase activities occurred in the recovery fish. The MR cells in the branchial epithelia showed a strong Na(+), K(+)-ATPase immunoreactivity to carbaryl treatment indicating an activated MR cell function. The numerical MR cell density remained unchanged, but stretching of secondary gill lamellae as part of gill remodeling occurred during carbaryl exposure. The increased surface of these lamellae with abundant MR cells as a result of its migration into the lamellar surface points to marked structural and functional modifications of these cells in the carbaryl-treated fish which is likely to a target for carbaryl action. The rise in plasma T(4) and the restoration of normal branchial epithelia in the recovery fish indicate a thyroidal involvement in the recovery response and survival. Our data thus provide evidence that carbaryl exposure and its recovery evoke interrenal and thyroid disruption in this fish leading to a modified osmotic response including an altered MR cell function.

Mixture toxicity assessment of wood preservative pesticides in the freshwater amphipod Gammarus pulex (L.)

All over the world, insecticides and fungicides are used to protect wood against pathogens. To document the environmental toxicity of wood preservative mixtures, freshwater amphipods Gammarus pulex (L.) were submitted to organic pesticides given independently or in mixtures. When given independently at environmentally realistic concentrations, propiconazole and tebuconazole (triazoles fungicides) were not toxic for G. pulex, 3-iodo-2-propinyl butyl carbamate (IPBC, fungicide) was moderately toxic, and cypermethrin (pyrethroid insecticide) was extremely toxic. 96-h LC50 were, respectively, 4703, 1643, 604, and 0.09 microg L(-1). When amphipods were submitted to a mixture mimicking the composition of a commercial solution (18.2% of cypermethrin, 45.8% propiconazole, 17.2% tebuconazole, 18.8% IPBC), the overall toxicity was equal to that of the most toxic component, namely cypermethrin. But, when organisms were submitted to the real commercial mixture containing pesticides, solvents and additives, the toxic effects were markedly higher. Moreover, a third mixture with only 0.002% cypermethrin showed lethality 2.5-18-fold higher than those predicted by the commonly used models. The present results show that toxicity of wood preservative mixtures cannot be assessed starting only from the toxicities of each single component. Furthermore, the present data strongly suggest that the environmental impacts of wood preservative mixtures might be frequently underestimated.

The effects of the herbicide metolachlor on agonistic behavior in the crayfish, Orconectes rusticus

Previous research suggests that agricultural herbicides interfere with olfactory-mediated behavior, such as responses to alarm signals and the ability to locate food, in aquatic organisms. In crayfish, aggressive interactions are also mediated by chemical signals. These social signals are important in establishing dominance, which in turn has an impact on an individual's ability to find and use mates, food, and habitat space. In this study, we investigated the impact of exposure to sublethal levels of the herbicide metolachlor on the ability of crayfish to respond to olfactory signals used in agonistic behaviors. Crayfish were exposed to three different environmentally relevant concentrations (60 ppb, 70 ppb, and 80 ppb) of metolachlor for 96 hours. Each exposed crayfish was then placed in a fight arena and was allowed to interact with a naïve, untreated crayfish for 15 minutes. We analyzed several characteristics of fighting behavior, including initial aggressiveness, time to fight, intensity levels, duration, number of encounters, and the winner and loser of each fight. Crayfish exposed to 80 ppb metolachlor were less likely to initiate and win encounters against naïve conspecifics than any other treatment group. Analysis of fight dynamics shows that metolachlor does not alter the temporal fighting dynamics within crayfish aggression. We conclude that high sublethal concentrations of metolachlor may be interfering with the ability of crayfish to receive or respond to social signals and thus affect certain agonistic behaviors.

Diethyldithiocarbamate injection induces transient oxidative stress in goldfish tissues

The effects of intraperitoneal injection of diethyldithiocarbamate (DDC) on free radical processes were examined in brain, liver and kidney of goldfish (Carassius auratus). Levels of oxidatively modified lipids and proteins as well as the activities of antioxidant and associated enzymes were measured. Intraperitoneal injection of DDC at a concentration of 0.01 mg/g wet mass decreased SOD activities by about 30-50% after 48 and 168 h compared to corresponding sham-injected values. This treatment resulted in transient oxidative stress. Lipid peroxide content increased after DDC injection at all time points in the kidney, after 48 h in the liver and was elevated in most experimental groups in the brain. Thiobarbituric-acid reactive substances (end products of lipid peroxidation) rose within the first 48 h after injection, but returned to initial levels after 168 h. Two other indices of oxidative stress were also transiently modified: protein carbonyl levels in the brain and kidney increased 24h post-injection, and the low-molecular mass thiol content was reduced over the same period in all tissues examined. Activities of catalase, glutathione peroxidase, glutathione-S-transferase, glutathione reductase, and glucose-6-phosphate dehydrogenase showed differential responses to DDC treatment that rebounded by 168 h post-injection. Glutathione peroxidase activities were reduced by 60, 45 and 65% in the brain, liver and kidney, respectively, after 24h but rebounded thereafter. After 48 h post-injection with DDC significant decreases were also seen in liver and kidney catalase, GST activities in all three tissues, and kidney GR and G6PDH activities. In some cases, catalase, GST, GR and G6PDH activities transiently increased after 24 h. It was concluded that DDC injection depleted SOD and simultaneously stimulated lipid peroxidation, but did not require compensatory enhancement of other enzymatic defenses. Different actions of the superoxide anion in cellular metabolism and possible consequences of the impairment of superoxide dismutase are discussed.