Behaviour, physiology and carotenoid pigmentation in Arctic charr Salvelinus alpinus

Effects of thermal stress responses in goldfish (Carassius auratus): growth performance, total carotenoids and coloration, hematology, liver histology, and critical thermal maximum

The present study aimed to investigate the effect of thermal stress on growth, feed utilization, coloration, hematology, liver histology, and critical thermal maximum (CTmax) in goldfish (Carassius auratus) cultured at three different acclimation temperatures including 27 °C, 30 °C, and 34 °C for 10 weeks. Goldfish were assigned randomly to tanks with a quadruplicate setup, accommodating 20 fish per tank. The result showed that fish acclimated to different temperatures did not significantly differ in weight gain (WG) and specific growth rate (SGR). However, increasing temperature significantly decreased feed efficiency ratio (FER), protein efficiency ratio (PER), and protein productive value (PPV), but significantly increased feed conversion ratio (FCR) (P < 0.05). The coloration parameters significantly decreased by high temperature in the trunk region with increasing temperature (L* and a* at week 5; L*, a*, and b* at week 10; P < 0.05). Total carotenoid contents in serum, fin, muscle, and skin also significantly decreased with increasing temperature (P < 0.05). Total protein, albumin, and globulin levels exhibited a notable decrease, while the albumin: globulin ratio showed a slight insignificant increase, with increasing temperature. Aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), total cholesterol, and triglycerides significantly increased with increasing temperature (P < 0.05). While, high-density lipoprotein cholesterol (HDL-c) decreased linearly (P < 0.05). Glucose and cortisol levels linearly increased with increasing temperature, the highest levels being observed in the 34 °C group. Liver histology showed swollen hepatocytes, nuclei displacement, and infiltration of inflammation in fish cultured at 34 °C. Goldfish acclimated to 34 °C displayed a higher CTmax of 43.83 °C compared to other groups. The present study showed that temperature should be kept below 34 °C for goldfish culture to prevent high FCR, fading coloration, and liver damages.

Sex-specific effects of inbreeding on body colouration and physiological colour change in the cichlid fish Pelvicachromis taeniatus

Background

Colour expression is highly variable in animals. In fishes, rapid colour change, i.e. physiological colour change, can be observed in multiple contexts, e.g. in camouflage or communication, and is affected by various factors, such as stress. Pelvicachromis taeniatus is a cichlid fish from West Africa with sexual dichromatism and both sexes being brightly coloured and flexible in ornament expression. In the present study, inbred and outbred P. taeniatus were photographed before and after a stress situation to investigate the stress response regarding colour expression in both sexes.

Results

The chromaticity and the colour patch size (relative coloured area at the abdomen) were determined at both timepoints and the changes were analysed. Additionally, the coefficients of variation within family groups for the chromaticity (CV_chromaticity) and colour patch size (CV_area) were calculated. Chromaticity as well as the extent of colouration increased significantly following handling stress. The change in chromaticity was not significantly different between in- and outbred individuals in females and males. Inbred males showed more intense yellow colouration than outbred males. Independent from inbreeding, the CV_chromaticity decreased following the handling stress. The change in CV_area of females and males differed between in- and outbred individuals. In females, the decrease was significantly stronger in inbred individuals and in males the decrease was stronger in the outbred group.

Conclusion

The results show that short-term stress can increase colouration, potentially advertising individual’s stress tolerance. Furthermore, this study shows positive inbreeding effects on a sexually selected trait.

White-edged cowards: high-pitched treefrogs will be attacked by those with orange legs

Anurans are one of the most diverse groups of animals, with single and multi-modal communication forms commonly used to settle disputes over territory and to attract females. Thus, I aimed to evaluate if male white-edged treefrogs tend to attack smaller individuals and which morphometric factor is related to it. Advertisement calls of this species were recorded and used in a four-choice experiment with the emission of artificially designed calls. I evaluated which speaker individuals approached and if morphometric variables could predict it. I observed that individuals approached significantly more often towards the high-pitched call than other treatments, and the frequency to do so was predicted by the extension of orange colour in their legs. These results indicate that smaller individuals are actively excluded from calling sites.

Proof of concept: visual categorization of carotenoid pigmentation in Arctic charr (Salvelinus alpinus L) can predict stress response

Carotenoid pigmentation in Salvelinus alpinus has been connected to stress responsiveness in earlier studies. This has, however, only been tested with time-consuming image analysis from photos. Here, we used quick visual categorization of carotenoid pigmentation to investigate the stress responsiveness of the extreme groups. The visually selected charr were then exposed to a net restraint stressor. Arctic charr with few spots also had a lower stress responsiveness compared to charr with many spots. Thus, visual selection could be used as a simple method within aquaculture.

Wasteful carotenoid coloration and its effects on territorial behavior in a cichlid fish

The famously diverse body coloration of cichlid fish serves communicative functions in mating and social interactions including competition for resources. Here, we examined the effects of a color pattern trait-the width of a yellow bar on a black body-on territorial competition in males and females of a color variant ("Ikola") of the Lake Tanganyika cichlid Tropheus. First, measuring integumentary carotenoid concentrations in the yellow and black body regions, we established that wider yellow bars require more carotenoids allocated to body coloration. However, we also detected high carotenoid concentrations in the black body regions (> 100 µg/g fresh skin), raising questions about the function of non-displayed integumentary carotenoids. Behavioral experiments showed that fish with wider bars were quicker to explore an unfamiliar area of the tank. In experiments including presentations of fish dummies, the bar width of 'territorial' dummies had no effect on the latency time which test fish took to intrude into the dummies' territories. However, male test fish performed fewer aggressive acts against wide-barred than against narrow-barred dummy competitors. Our results suggest that intimidation by wide bars as well as correlations between bar width and explorative behavior may contribute to mediating success in territorial Tropheus "Ikola".

Embryonic development, locomotor behavior, biochemical, and epigenetic effects of the pharmaceutical drugs paracetamol and ciprofloxacin in larvae and embryos of Danio rerio when exposed to environmental realistic levels of both drugs

For several years, the scientific community has been concerned about the presence of pharmaceuticals in the wild, since these compounds may have unpredictable deleterious effects on living organisms. Two examples of widely used pharmaceuticals that are present in the environment are paracetamol and ciprofloxacin. Despite their common presence in the aquatic environment due to their poor removal by sewage treatment plants, knowledge concerning their putative toxic effects is still scarce. This work aimed to characterize the effects of paracetamol (0.005, 0.025, 0.125, 0.625, and 3.125 mg/L) and ciprofloxacin (0.005, 0.013, 0.031, 0.078, 0.195, and 0.488 μg/L) in zebrafish embryos and larvae, exposed to environmentally relevant levels, close to the real concentrations of these pharmaceuticals in surface waters and effluents. The adopted toxic end points were developmental, a behavioral parameter (total swimming time), and a biomarker-based approach (quantification of the activities of catalase, glutathione-S-transferase, cholinesterases, glutathione peroxidase, and lipid peroxidation levels) combined with epigenetic analysis (immunohistochemical detection of 5-methylcytidine). Exposure to paracetamol had effects on all of the adopted toxic end points; however, ciprofloxacin only caused effects on behavioral tests and alterations in biomarkers. It is possible to ascertain the occurrence of oxidative stress following exposure to both drugs, which was more evident regarding paracetamol, an effect that may be related to the observed epigenetic modifications.

Consistent individual competitive ability in rainbow trout as a proxy for coping style and its lack of correlation with cortisol responsiveness upon acute stress

For a given fish species, individuals are different in their ability to cope with stressors; each individual has its own set of physiological and behavioral responses to stress (stress-coping style). This individual diversity is of importance when considering the welfare of fish reared in aquaculture facilities. In this study with rainbow trout (Oncorhynchus mykiss) we investigated the link between the ability to compete for food of each individual (used as a proxy of dominance behavior/proactive stress-coping style) and its ability to cope with stress; we hypothesized that fish that are better competitors would be more robust against common aquaculture stressors. We screened 680 rainbow trout individuals for competition ability. This was done by submitting groups of 20 individuals to a 1-week competition trial where they were kept at low stocking density and were provided a restricted amount of food. A 15% of the screened fish were selected as "winners" and another 15% were selected as "losers", based on growth rates during the competition trials. Fish were re-tested in a second competition trial after several weeks, to assess for consistency of competitive ability. Winner and loser fish were individually exposed to confinement and their neuroendocrine stress response was evaluated (serotonergic activity in telencephalon and brain stem, plasma levels of cortisol, glucose and lactate). Furthermore, behavioral responses to confinement and net restraining tests were also investigated. The results showed good temporal consistency of competitive ability in the lapse of time of the experiments. Besides, competitive ability showed a positive association to fish activity during the net restraining tests. However, plasma stress marker data showed a lack of relevant differences between the acute stress responses of winner and loser fish, adding up to the body of evidence suggesting that stress responsiveness might not be consistently linked to SCS in vertebrates. This, together with the inability of winner fish to outperform loser fish in usual stocking density conditions, suggests that there is no clear welfare or performance benefits in selecting fish of a specific coping style for fish farming, at least in the domesticated trout population used in the current study.

Behavior and histopathology as biomarkers for evaluation of the effects of paracetamol and propranolol in the neotropical fish species Phalloceros harpagos

Pharmaceutical drugs in the aquatic environment can induce adverse effects on nontarget organisms. This study aimed to assess the short-term effects of sublethal concentrations of both paracetamol and propranolol on the fish Phalloceros harpagos, specifically light/dark preference, swimming patterns, skin pigmentation, histopathology, and liver glycogen levels. Fish were acutely exposed to sublethal concentrations of both paracetamol (0.008, 0.08, 0.8, 8, 80 mg L^-1) and propranolol (0.0001, 0.001, 0.01, 0.1, 1 mg L^-1) under controlled conditions. For scototaxis, a significant preference for the dark compartment was observed for the group exposed to the highest concentration of paracetamol (80 mg L^-1). Propranolol exposure significantly altered the swimming pattern, especially in fish exposed to the 0.001 mg L^-1 concentration. Pigmentation was reduced in propranolol-exposed fish (0.1, 1 mg L^-1). The lowest concentration of propranolol (0.0001 mg L^-1) induced a decrease of histochemical reaction for hepatic glycogen. These data demonstrate that pharmaceuticals can induce sublethal effects in nontarget organisms, even at low concentrations, compromising specific functions of the individual with ecological relevance, such as energy balance and behavior.

Neural and behavioural correlates of repeated social defeat

Dominance hierarchies are common across the animal kingdom and have important consequences for reproduction and survival. Animals of lower social status cope with repeated social defeat using proactive and reactive behaviours. However, there remains a paucity of information on how an individual’s coping behaviours changes over time or what neural mechanisms are involved. We used a resident-intruder paradigm in the African cichlid fish Astatotilapia burtoni to investigate the neural correlates of these two opposing behaviour groups. Fish initially used both proactive and reactive behaviours, but had a dramatic increase in use of proactive behaviours during the third interaction, and this was followed by cessation of proactive behaviours and exclusive use of reactive coping. By quantifying neural activation in socially-relevant brain regions, we identify a subset of brain nuclei, including those homologous to the mammalian amygdala, showing higher activation in fish displaying proactive but not reactive behaviours. Fish displaying reactive behaviours had greater neural activation in the superior raphe, suggesting a possible conserved function during social defeat across vertebrates. These data provide the first evidence on the involvement of specific brain regions underlying proactive and reactive coping in fishes, indicating that these nuclei have conserved functions during social defeat across taxa.

Serotonin Coordinates Responses to Social Stress-What We Can Learn from Fish

Social interaction is stressful and subordinate individuals are often subjected to chronic stress, which greatly affects both their behavior and physiology. In teleost fish the social position of an individual may have long-term effects, such as effects on migration, age of sexual maturation or even sex. The brain serotonergic system plays a key role in coordinating autonomic, behavioral and neuroendocrine stress responses. Social subordination results in a chronic activation of the brain serotonergic system an effect, which seems to be central in the subordinate phenotype. However, behavioral effects of short-term acute activation of the serotonergic system are less obvious. As in other vertebrates, divergent stress coping styles, often referred to as proactive and reactive, has been described in teleosts. As demonstrated by selective breeding, stress coping styles appear to be partly heritable. However, teleost fish are characterized by plasticity, stress coping style being affected by social experience. Again, the brain serotonergic system appears to play an important role. Studies comparing brain gene expression of fish of different social rank and/or displaying divergent stress coping styles have identified several novel factors that seem important for controlling aggressive behavior and stress coping, e.g., histamine and hypocretin/orexin. These may also interact with brain monoaminergic systems, including serotonin.

Maternal allocation of carotenoids increases tolerance to bacterial infection in brown trout

Life-history theory predicts that iteroparous females allocate their resources differently among different breeding seasons depending on their residual reproductive value. In iteroparous salmonids there is typically much variation in egg size, egg number, and in the compounds that females allocate to their clutch. These compounds include various carotenoids whose functions are not sufficiently understood yet. We sampled 37 female and 35 male brown trout from natural streams, collected their gametes for in vitro fertilizations, experimentally produced 185 families in 7 full-factorial breeding blocks, raised the developing embryos singly (n = 2960), and either sham-treated or infected them with Pseudomonas fluorescens. We used female redness (as a measure of carotenoids stored in the skin) and their allocation of carotenoids to clutches to infer maternal strategies. Astaxanthin contents largely determined egg colour. Neither egg weight nor female size was correlated with the content of this carotenoid. However, astaxanthin content was positively correlated with larval growth and with tolerance against P. fluorescens. There was a negative correlation between female skin redness and the carotenoid content of their eggs. Although higher astaxanthin contents in the eggs were associated with an improvement of early fitness-related traits, some females appeared not to maximally support their current offspring as revealed by the negative correlation between female red skin colouration and egg carotenoid content. This correlation was not explained by female size and supports the prediction of a maternal trade-off between current and future reproduction.

Brain cortisol receptor expression differs in Arctic charr displaying opposite coping styles

Individually consistent behavioral and physiological responses to stressful situations (often referred to as coping styles) has been reported in many animal species. Differences in hypothalamic-pituitary axis reactivity characterize individuals, and it has been proposed that the glucocorticoid (gr) and mineralocorticoid (mr) receptors are fundamental in regulating coping styles. We sorted individuals into reactive and proactive coping styles by collapsing behavioral outputs from net restraint and confinement stress tests in a principal component analysis. We then analyzed plasma cortisol levels, serotonin neurochemistry and the relative mRNA expression of gr1 and mr in stressed individuals per coping style. Proactive fish were characterized as having a lower serotonergic activity and being more active under stress. In addition, proactive fish had higher hypothalamic gr1 and mr abundance and a higher mr/gr1 ratio, compared to reactive fish. We found no significant differences in cortisol or telencephalic mRNA, gr1 and mr expression, or their ratio. Brain MR and GR have been proven to have an important role in the appraisal, coping and adaptation to stressful stimuli, so that a higher expression of these receptors in proactive fish suggests increased tolerance and performance under stress, compared to reactive individuals. We present evidence of a conserved neuroendocrine mechanism associated with coping styles in a fish species which is ecologically very diverse and considered to be the most cold-adapted fish in freshwater. We propose that this may be a first step into exploiting this model in order to better understand climate-change related effects in sub populations and ecophenotypes.

Short-term stress: effects on cortisol levels and carotenoid spots in Arctic char (Salvelinus alpinus)

Earlier studies have shown that the carotenoid pigmentation in Arctic char (Salvelinus alpinus (L., 1758)) is connected to stress responsiveness. These studies also suggested that the pigmentation is dynamic and can change quickly. Therefore, we wanted to investigate the effect of a short-term stressor on the number of carotenoid spots before and after certain time intervals after the stressor. Individuals were exposed to a net-restraint stressor for 1 min and then assigned a recovery time of either 0, 1, 2, 8, or 24 h. Photographs were taken before the stressor and after the recovery time to count carotenoid spots and to look at the relative changes over time. Behaviour during the stressor and cortisol levels after the assigned recovery time were evaluated. We found that the change in spottiness, measured as the ratio of spots after and before the stressor, changed with recovery time on the right side but not on the left side. Furthermore, left-side spots were correlated with struggling activity. Thus, carotenoid pigmentation seems to be lateralized, with more static spots on the left side connected to stress responsiveness, whereas spots on the right side seem to be more dynamic.

Behavioural responses in a net restraint test predict interrenal reactivity in Arctic charr Salvelinus alpinus

In this study, a 1 min net restraint test was evaluated as a method to predict stress-coping style in Arctic charr Salvelinus alpinus, by investigating the relationship between behaviour during the test and levels of plasma cortisol sampled after 30 min confinement. In two separate groups of S. alpinus, general linearized model revealed significant correlations between cortisol levels and principal component scores extracted from principal component analysis, combining measures of activity in the tests. With the use of glmulti, the model selection ruled out any effects of size, sex and order of capture on interrenal reactivity. In general, S. alpinus that were more active in the net restraint test also had low levels of circulating cortisol, suggesting a proactive coping style. The results from two repeated runs were not correlated, but both runs, performed eight days apart, show a negative correlation between post-stress cortisol level and activity in the net. The lack of consistency could be explained by different treatments before each run and individual differences in behavioural plasticity. The net restraint test is thus predictive of stress-coping style in S. alpinus, and has the benefit of being less time-consuming than the commonly used confinement stress test.

Social stress effects on pigmentation and monoamines in Arctic charr

Pigmentation often signals status and in general melanin-based pigmentation is indicative of aggression and stress resilience in vertebrates. This is evident in the salmonids Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) where more melanin spotted individuals are more stress resilient. However, in the salmonid Arctic charr (Salvelinus alpinus) it seems as if it is carotenoid-based pigmentation that signals aggression and stress resilience. In our study, social stress effects on carotenoid-based spots, and behavioural and physiological stress responses were investigated. Socially stressed individuals have more spots, and behavioural stress responses were associated with spots. Some of the results concerning physiological stress responses, such as plasma cortisol levels and monoaminergic activity, are associated with spottiness. Further, the earlier proposed lateralization of spots, with left side connected to stress responsiveness and right side to aggression, is to some extent validated although not conclusively. In conclusion, this study provides further evidence that more stressed charr have more carotenoid spots, and for the first time monoaminergic activity is shown to be connected with carotenoid pigmentation.

Dominance and stress signalling of carotenoid pigmentation in Arctic charr (Salvelinus alpinus): lateralization effects?

Social conflicts are usually solved by agonistic interactions where animals use cues to signal dominance or subordinance. Pigmentation change is a common cue used for signalling. In our study, the involvement of carotenoid-based pigmentation in signalling was investigated in juvenile Arctic charr (Salvelinus alpinus). Size-matched pairs were analysed for pigmentation both before and after being tested for competitive ability. We found that dominant individuals had fewer carotenoid-based spots on the right and left sides as well as lower plasma cortisol levels compared to subordinate individuals. Further, the number of spots on both sides was positively associated with plasma cortisol levels. These results indicate that carotenoid-based pigmentation in Arctic charr signals dominance and stress coping style. Further, it also appears as if carotenoid-based pigmentation is lateralized in Arctic charr, and that the right side signals aggression and dominance whereas the left side signals stress responsiveness.

Behavioural stress responses predict environmental perception in European sea bass (Dicentrarchus labrax)

Individual variation in the response to environmental challenges depends partly on innate reaction norms, partly on experience-based cognitive/emotional evaluations that individuals make of the situation. The goal of this study was to investigate whether pre-existing differences in behaviour predict the outcome of such assessment of environmental cues, using a conditioned place preference/avoidance (CPP/CPA) paradigm. A comparative vertebrate model (European sea bass, Dicentrarchus labrax) was used, and ninety juvenile individuals were initially screened for behavioural reactivity using a net restraining test. Thereafter each individual was tested in a choice tank using net chasing as aversive stimulus or exposure to familiar conspecifics as appetitive stimulus in the preferred or non preferred side respectively (called hereafter stimulation side). Locomotor behaviour (i.e. time spent, distance travelled and swimming speed in each tank side) of each individual was recorded and analysed with video software. The results showed that fish which were previously exposed to appetitive stimulus increased significantly the time spent on the stimulation side, while aversive stimulus led to a strong decrease in time spent on the stimulation side. Moreover, this study showed clearly that proactive fish were characterised by a stronger preference for the social stimulus and when placed in a putative aversive environment showed a lower physiological stress responses than reactive fish. In conclusion, this study showed for the first time in sea bass, that the CPP/CPA paradigm can be used to assess the valence (positive vs. negative) that fish attribute to different stimuli and that individual behavioural traits is predictive of how stimuli are perceived and thus of the magnitude of preference or avoidance behaviour.

Carotenoid-based coloration in cichlid fishes

Animal colors play important roles in communication, ecological interactions and speciation. Carotenoid pigments are responsible for many yellow, orange and red hues in animals. Whereas extensive knowledge on the proximate mechanisms underlying carotenoid coloration in birds has led to testable hypotheses on avian color evolution and signaling, much less is known about the expression of carotenoid coloration in fishes. Here, we promote cichlid fishes (Perciformes: Cichlidae) as a system in which to study the physiological and evolutionary significance of carotenoids. Cichlids include some of the best examples of adaptive radiation and color pattern diversification in vertebrates. In this paper, we examine fitness correlates of carotenoid pigmentation in cichlids and review hypotheses regarding the signal content of carotenoid-based ornaments. Carotenoid-based coloration is influenced by diet and body condition and is positively related to mating success and social dominance. Gaps in our knowledge are discussed in the last part of this review, particularly in the understanding of carotenoid metabolism pathways and the genetics of carotenoid coloration. We suggest that carotenoid metabolism and transport are important proximate mechanisms responsible for individual and population-differences in cichlid coloration that may ultimately contribute to diversification and speciation.