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Background: Progressive CO2-induced ocean acidification (OA) impacts marine life in ways that are difficult to predict but are likely to become exacerbated over generations. Although marine fishes can balance acid–base homeostasis efficiently, indirect ionic regulation that alter neurosensory systems can result in behavioural abnormalities. In marine invertebrates, OA can also affect immune system function, but whether this is the case in marine fishes is not fully understood. Farmed fish are highly susceptible to disease outbreak, yet strategies for overcoming such threats in the wake of OA are wanting. Here, we exposed two generations of the European sea bass (Dicentrarchus labrax) to end-of-century predicted pH levels (IPCC RCP8.5), with parents (F1) being exposed for four years and their offspring (F2) for 18 months. Our design included a transcriptomic analysis of the olfactory rosette (collected from the F2) and a viral challenge (exposing F2 to betanodavirus) where we assessed survival rates. Results: We discovered transcriptomic trade-offs in both sensory and immune systems after long-term transgenerational exposure to OA. Specifically, RNA-Seq analysis of the olfactory rosette, the peripheral olfactory organ, from 18-months-old F2 revealed extensive regulation in genes involved in ion transport and neuronal signalling, including GABAergic signalling. We also detected OA-induced up-regulation of genes associated with odour transduction, synaptic plasticity, neuron excitability and wiring and down-regulation of genes involved in energy metabolism. Furthermore, OA-exposure induced up-regulation of genes involved in innate antiviral immunity (pathogen recognition receptors and interferon-stimulated genes) in combination with down-regulation of the protein biosynthetic machinery. Consistently, OA-exposed F2 challenged with betanodavirus, which causes damage to the nervous system of marine fish, had acquired improved resistance. Conclusion: F2 exposed to long-term transgenerational OA acclimation showed superior viral resistance, though as their metabolic and odour transduction programs were altered, odour-mediated behaviours might be consequently impacted. Although it is difficult to unveil how long-term OA impacts propagated between generations, our results reveal that, across generations, trade-offs in plastic responses is a core feature of the olfactory epithelium transcriptome in OA-exposed F2 offspring, and will have important consequences for how cultured and wild fish interacts with its environment. [ABSTRACT FROM AUTHOR]

Bolder individuals have greater access to food sources and reproductive partners but are also at increased risk of predation. Boldness is believed to be consistent across time and contexts, but few studies have investigated the stability of this trait across variable environments, such as varying stress loads or long periods of time. Moreover, the underlying molecular components of boldness are poorly studied. Here, we report that boldness of 1154 European sea bass, evaluated using group risk-taking tests, is consistent over seven months and for individuals subjected to multiple environments, including a chronically stressful environment. Differences in risk-taking behaviour were further supported by differences observed in the responses to a novel environment test: shy individuals displayed more group dispersion, more thigmotaxic behaviour and lower activity levels. Transcriptomic analyses performed on extreme phenotypes revealed that bold individuals display greater expression for genes involved in social and exploration behaviours, and memory in the pituitary, and genes involved in immunity and responses to stimuli in the head kidney. This study demonstrates that personality traits come with an underpinning molecular signature, especially in organs involved in the endocrine and immune systems. As such, our results help to depict state–behaviour feedback mechanisms, previously proposed as key in shaping animal personality. [ABSTRACT FROM AUTHOR]

Background: Consistent individual differences in behaviour, known as animal personalities, have been demonstrated within and across species. In fish, studies applying an animal personality approach have been used to resolve variation in physiological and molecular data suggesting a linkage, genotype-phenotype, between behaviour and transcriptome regulation. In this study, using three fish species (zebrafish; Danio rerio, Atlantic salmon; Salmo salar and European sea bass; Dicentrarchus labrax), we firstly address whether personality-specific mRNA transcript abundances are transferrable across distantly-related fish species and secondly whether a proactive transcriptome signature is conserved across all three species. Results: Previous zebrafish transcriptome data was used as a foundation to produce a curated list of mRNA transcripts related to animal personality across all three species. mRNA transcript copy numbers for selected gene targets show that differential mRNA transcript abundance in the brain appears to be partially conserved across species relative to personality type. Secondly, we performed RNA-Seq using whole brains from S. salar and D. labrax scoring positively for both behavioural and molecular assays for proactive behaviour. We further enriched this dataset by incorporating a zebrafish brain transcriptome dataset specific to the proactive phenotype. Our results indicate that cross-species molecular signatures related to proactive behaviour are functionally conserved where shared functional pathways suggest that evolutionary convergence may be more important than individual mRNAs. Conclusions: Our data supports the proposition that highly polygenic clusters of genes, with small additive effects, likely support the underpinning molecular variation related to the animal personalities in the fish used in this study. The polygenic nature of the proactive brain transcriptome across all three species questions the existence of specific molecular signatures for proactive behaviour, at least at the granularity of specific regulatory gene modules, level of genes, gene networks and molecular functions. [ABSTRACT FROM AUTHOR]

Temperature‐dependent sex determination (TSD) can be observed in multiple reptile and fish species. It is adaptive when varying environmental conditions advantage either males or females. A good knowledge of the thermosensitive period is key to understand how environmental changes may lead to changes in population sex ratio. Here, by manipulating temperature during development, we confirm that cold temperature (16°C) increases the proportion of fish that develop as females in European sea bass (Dicentrarchus labrax) until 56 days posthatching, but show that it has an opposite effect at later stages, with the proportion of males reaching ~90% after 230 days at 16°C. This is the first observation of opposite effects of temperature at different time periods on the sex ratio of a vertebrate. Our results highlight the potential complexity of environmental effects on sex determination. [ABSTRACT FROM AUTHOR]

To understand the genetic basis of coping style in European seabass, fish from a full factorial mating (10 females x 50 males) were reared in common garden and individually tagged. Individuals coping style was characterized through behavior tests at four different ages, categorizing fish into proactive or reactive: a hypoxia avoidance test (at 255 days post hatching, dph) and 3 risk-taking tests (at 276, 286 and 304 dph). We observed significant heritability of the coping style, higher for the average of risk-taking scores (h2 = 0.45 ± 0.14) than for the hypoxia avoidance test (h2 = 0.19 ± 0.10). The genetic correlations between the three risk-taking scores were very high (rA = 0.96–0.99) showing that although their repeatability was moderately high (rP = 0.64–0.72), successive risk-taking tests evaluated the same genetic variation. A mild genetic correlation between the results of the hypoxia avoidance test and the average of risk-taking scores (0.45 ± 0.27) suggested that hypoxia avoidance and risk-taking tests do not address exactly the same behavioral and physiological responses. Genetic correlations between weight and risk taking traits showed negative values whatever the test used in our population i.e. reactive individual weights were larger. The results of this quantitative genetic analysis suggest a potential for the development of selection programs based on coping styles that could increase seabass welfare without altering growth performances. Overall, it also contributes to a better understanding of the origin and the significance of individual behavioral differences. [ABSTRACT FROM AUTHOR]

Replacing aquaculture feeds based on fisheries-derived resources with plant-based diets could be a relevant strategy to improve the sustainability of aquaculture. Recent studies on sea bass have shown that the total and early replacement of marine products by plant products would have a moderate effect on fish growth and body lipid content. Whether a plant-based diet impacts behavioural and physiological traits possibly linked to fish welfare, is not known, however. Here, we studied the effect of a totally plant-based diet introduced at an early stage of sea bass development on self-feeding behaviour, learning ability in a T-maze and stress biomarkers. We first compared learning processes in self-feeding conditions, between naive fish fed a plant-based diet (PBF) and fish fed a classic marine diet (MF). Then, we tested fish individually in a T-maze to compare the two feed groups for swimming activity, exploration and the ability to learn to discriminate between two two-dimensional objects associated with a reward. Blood physiological variables, including stress indicators (cortisol and glucose concentrations), were also determined. We did not find any indications of differences in self-feeding behaviour between PBF and MF in the first 30 days. A second experiment showed similar swimming activities in both fish categories. The “no-choice” percentage was high in both fish categories (~60%), but all the fish moved preferentially toward the reward. Their first turns indicated an ability to discriminate between two two-dimensional objects to complete a simple task. However, the high percentage of “no-choice” responses in both fish categories could have rendered the results non significant. The T-maze test procedure induced the production of high concentrations of cortisol, indicating acute stress in fish of both groups during testing. Plasma cortisol concentration was higher in MF than PBF, suggesting that the plant-based diet may affect the short-term release of cortisol. This study provides the first insight into the impact of a plant-based diet on sea bass behavioural traits, and confirms the effect of this diet on cortisol release in response to stress. Overall, in this first experiment, we did not find any major impact of a plant-based diet on sea bass behavioural traits, which is an interesting point for the development potential of such a sustainable aquaculture strategy. [ABSTRACT FROM AUTHOR]

Abstract: In various experiments under self-feeding conditions, sea bass groups could be divided into three categories regarding feeder actuation: high, low and zero-triggering fish. In all cases few high-triggering fish were responsible for a high percentage of the feed delivery. A question was raised about the role played by feeding motivation in such high-triggering status acquisition. It was approached by applying a 3-week fasting period in order to induce similar negative specific growth rate (SGR) in two groups of fish of similar mean weight but with either a low or a high coefficient of variation for weight (CVw) (Tlow: CVw ∼11%, 3 tanks of 60 fish each; Thigh: CVw ∼20%, 3 tanks of 60 fish each). These groups were created to test the consistency of behavioural responses in two different contexts (i.e. two population size-distributions). During the follow-up period of 40 days, the group level feed-demand behaviour was not strongly modified by the fasting period and there were no differences between Tlow and Thigh groups. Complete growth compensation was the same in all tanks as observed at the end of the experiment. At the individual level, high-triggering fish were exactly the same individuals before and after the fasting period. Up to four high-triggering fish could be observed according to the tank and when several fish were performing high-triggering activity, their rankings were sometimes reversed after the fasting period. High-triggering fish increased their activity levels after the fasting period showing behavioural plasticity. High-triggering status could neither be explained by an initial lower SGR nor a sex effect, nor by any of the measured physiological blood parameters. Thus, individual''s triggering activity levels could be related to personality and/or metabolic traits but further research is required to confirm this assumption. [Copyright &y& Elsevier]

This study aims to test the influence of size grading on self-feeding behaviour, social structure (measured by the percentage of triggering acts per individual), growth performances, and blood physiological variables of individually passive integrated transponder (PIT)-tagged sea bass juveniles, using a computerized on-demand feeding system coupled with a PIT tag monitoring device. Three consecutive periods of 27 days each were compared: a first period (P1) before grading (6 tanks of 100 fish; 40.2 ± 8.9 g) followed by a second period (P2) after grading. The protocol applied aimed to create two groups of fish of similar mean weight but with either a low or a high coefficient of variation of weight (CVw) corresponding to an imposed difference in social disruption (Tlow: CVw ~ 10%, 3 tanks of 60 fish each with social disruption; Thigh:CVw ~20%, 3 tanks of 60 fish each, without social disruption). Tlow and Thigh groups were studied over P2, and an additional 27-day period under identical conditions (P3). The grading protocol used and/or time modified the social structure when comparing P1 and P2. Thereafter, during P2 and P3, no difference could be observed in growth performances, feed demand, or physiological variables between Tlow and Thighgroups. Feeding rhythms and social structures were similar in both groups. In conclusion, such grading practice only transiently modifies feed demand behaviour and social structure built around the self-feeder, without further improvement in individual growth performances in sea bass. [ABSTRACT FROM PUBLISHER]

Among the strategies that can be used to improve fish welfare in a rearing environment, domestication and/or selective breeding was proposed to minimize fish responsiveness to husbandry practices. To verify this hypothesis on a recently domesticated species, the sea bass Dicentrarchus labrax, two experiments were realized, each using two populations differing according to their level of domestication or selection. For the first experiment, we used one population produced from wild parents (Wild; initial body mass: 106 ± 3 g), and one population from parents selected for growth for one generation (Selected 1; initial body mass: 129 ± 4 g). For the second experiment, we used one population produced from parents domesticated for two generations (Domesticated; initial body mass: 72 ± 3 g), and one produced from parents selected for growth for two generations (Selected 2; initial body mass: 89 ± 4 g). The first experiment was carried out over 112 days with 240 fish (60 fish per tank, 120 fish per population), and the second one over 84 days with 200 fish (50 fish per tank, 100 fish per population). Two variables, self-feeding behavior and growth performance, were measured over the time of the experiments. After a control period, the fish were submitted twice, at three-week intervals, to an acute stress treatment consisting of draining the tank and leaving the fish out of water for one minute. Both self-feeding behavior and growth performance were altered by the acute stress treatment. During the first post-stress period, the Domesticated and Selected (1 and 2) groups showed more pronounced post-stress exposure responses than the Wild fish: they modified their feeding rhythm, their feed intake, and their growth rate. During the second post-stress period, feeding rhythm was still affected (being more diurnal with a well defined peak), but the feed intake and growth rate results showed that the Domesticated and Wild groups seemed less affected than the Selected (1 and 2) populations, which continued to express a high post-stress response. According to these results, it can be concluded that: (1) an application of two acute stress treatments, at three-week intervals, modified fish feeding behavior and growth performance; (2) the domestication process seemed to improve fish adaptation abilities to this kind of stress; and (3) the process of selection for growth led to a final, better growth, but did not seem to improve fish acute stress tolerance. [ABSTRACT FROM PUBLISHER]

Abstract: Domestication and selection may affect fish behaviour, sometime as soon as at the first generation of domestication. However, knowledge about how both processes impact on fish spatial exploration and swimming activity still is to be improved. The objective of this experiment was (i) to evaluate spatial exploration behaviour and swimming activities of three sea bass strains having different domestication and selection levels and (ii) to analyse their responses to an acute stress. Sea bass exploration and swimming activities were studied before, during and 40min after a stimulation (standardized fall of an object). The experimental tank was divided in to four zones, and the time spent, the distance travelled in each zone and the swimming complexity were quantified for each period from video recording. Results showed that fish from all strains presented the same flight response and that stimulus exposure induced a significant decrease in exploratory behaviour and swimming activity. The present study has also demonstrated that only one generation of captivity could be sufficient to obtain fish presenting the same behavioural characteristics than fish reared since at least two generations. Moreover, this study has highlighted that selection for growth seemed to select fish characterized by a bolder personality and potentially better adapted to rearing environment. It allowed us to suggest that selection for growth may have a higher effect on fish personality than domestication only. [Copyright &y& Elsevier]

Fish are ectotherms and this means they are highly vulnerable to changes in ambient temperature, particularly during early developmental stages when temperature can induce persistent effects on phenotypic traits. In this study, the effect of egg incubation temperature on the response of juvenile European sea bass (Dicentrarchus labrax) to food deprivation and recovery after refeeding was assessed. Eggs were incubated at 11, 13.5 and 16 °C until hatching and then were reared at a common temperature until 9 months when fish were deprived of food for one week. The recovery from food deprivation was evaluated at 10 h and 2 days post-refeeding. Food deprivation in fish from eggs incubated at the highest temperature (16 °C) compared to 11 and 13.5 °C exhibited the most morphological and metabolic changes in the liver and foregut. Liver metabolism was changed as revealed by the significant reduction in lipid area and the increased number of hepatocyte nuclei. Foregut atrophy was coupled to a significant up-regulation of transcripts associated with gluconeogenesis (pck1) and peptide absorption (pept1). A modified metabolic response to the fast-refeed regime was revealed by the significantly decreased levels of plasma lactate, which may result from up-regulation of transcripts of the thyroid axis, deiodinase 2 (dio2) in the foregut. Fish incubated as eggs at a lower temperature (11 °C) exhibited less changes following the fast-refeed regime. Food deprivation did not significantly modify the morphology of the foregut and the liver parenchyma recovered sooner in fish from the 11 °C egg thermal regime compared to fish from the other thermal regimes following refeeding. The latter group of fish had a temporary stimulation of the GH-IGF axis with significant up-regulation of liver insulin-like growth factor I and II (igf-1 and igf-2) after fasting. The liver parenchyma of fish from the 13.5 °C egg thermal regime (the standard temperature of the hatchery stage) did not recover by the end of the experiment and transcripts of catalase (cat), encoding an antioxidant enzyme, were significantly downregulated compared to fish from the other egg thermal regimes. Our results suggest that thermal imprinting at the egg stage in European sea bass modified the juvenile metabolic response to food deprivation and the recovery response when feeding was resumed. • Egg thermal regime (ETR) modified the metabolic response to fasting/refeeding. • Higher ETR caused foregut atrophy in fish after fasting/refeeding. • Higher ETR caused up-regulation of pept1 , pck1 and dio2 after fasting/refeeding. • Lower plasma lactate levels occurred in fish from higher ETR. • Lower ETR caused up-regulation of Igf-1 and igf-2 after fasting/refeeding. [ABSTRACT FROM AUTHOR]

Coping styles consist of a coherent set of individual physiological and behavioral differences in stress responses that are consistent across time and context. Such consistent inter-individual differences in behavior have already been shown in European sea bass (Dicentrarchus labrax), but the associated mechanisms are still poorly understood. Here, we combine physiological measurements with individual behavioral responses in order to characterize coping styles in fish. Fish were tagged and placed in a tank for group risk-taking tests (GRT) at 8 months of age to evaluate boldness using the proxy latency of leaving a sheltered area towards an open area. A subsample of these fish were individually challenged 16 months later using an open field test (OFT), in which the boldness was assessed after being placed in a shelter within an open arena. Latency to exit the shelter, time spent in the shelter, and distance travelled were recorded for this purpose. The blood and brain were then collected to evaluate plasma cortisol concentration and neurotransmitter levels (dopamine, norepinephrine, serotonin, and related metabolites), as well as brain transcription of key genes involved in stress axis regulation (gr1, gr2 , mr, crf), neurogenesis (neurod1, neurod2, pcna), and neuronal development (egr1). Fish acting bolder in the GRT were not necessarily those acting bolder in the OFT, highlighting the relatively low consistency across different types of tests performed with a 16-months interval. There was, however, a significant correlation between stress markers and boldness. Indeed, mRNA levels of mr, crf, gr2, egr1 , and neurod2 , as well as norepinephrine levels were higher in shy than bold fish, whereas brain serotonergic activity was lower in shy fish. Overall, our study highlights the fact that boldness was not consistent over time when testing context differed (group vs. alone). This is in agreement with previous literature suggesting that social context play a key role in boldness measurement and that the particular life history of each individual may account in shaping the personality fate of a fish. • Boldness is not consistent when characterized using different types of test over an interval period of 16 months (group vs. individual tests). • After open field test, plasma cortisol concentration is similar between bold and shy fish. • Shy fish, however, display higher level of transcription of mr , gr2 , crf , egr1 and neurod2 (trend) in the whole brain. • Shy fish display higher level of norepinephrine and lower turnover ratio between serotonin and s hydroxyindoleacetic acid in the whole brain. [ABSTRACT FROM AUTHOR]

Fish skin is a multifunctional tissue that develops during embryogenesis, a developmental stage highly susceptible to epigenetic marks. In this study, the impact of egg incubation temperature on the regeneration of a cutaneous wound caused by scale removal in juvenile European sea bass was evaluated. Sea bass eggs were incubated at 11, 13.5 and 16 °C until hatching and then were reared at a common temperature until 9 months when the skin was damaged and sampled at 0, 1 and 3 days after scale removal and compared to the intact skin from the other flank. Skin damage elicited an immediate significant (p < 0.001) up-regulation of pcna in fish from eggs incubated at higher temperatures. In fish from eggs incubated at 11 °C there was a significant (p < 0.001) up-regulation of krt2 compared to fish from higher thermal backgrounds 1 day after skin damage. Damaged epidermis was regenerated after 3 days in all fish irrespective of the thermal background, but in fish from eggs incubated at 11 °C the epidermis was significantly (p < 0.01) thinner compared to other groups, had less goblet cells and less melanomacrophages. The thickness of the dermis increased during regeneration of wounded skin irrespective of the thermal background and by 3 days was significantly (p < 0.01) thicker than the dermis from the intact flank. The expression of genes for ECM remodelling (mmp9 , colXα, col1α1, sparc, and angptl2b) and innate immunity (lyg1 , lalba , sod1 , csf-1r and pparγ) changed during regeneration but were not affected by egg thermal regime. Overall, the results indicate that thermal imprinting of eggs modifies the damage-repair response in juvenile sea bass skin. • Egg thermal regime modified skin repair in juvenile fish. • Higher egg thermal regimes increased the regenerated epidermis thickness and up-regulated pcna. • Lower egg thermal regimes reduced the regenerated epidermis thickness and up-regulated krt2. • Skin damage to one flank caused molecular and morphological modifications in the undamaged flank. • The dermis was thicker in regenerated skin than in undamaged skin, irrespective of thermal background. [ABSTRACT FROM AUTHOR]

Biological variability is no longer considered as statistical noise, but rather as an adaptive benefit. This variability comes from consistent differences in behavioral and physiological responses among individuals to a changing/challenging environment, named “coping style”, “temperament” or “personality”. Many studies have described how to characterize personality traits and how to assess their consistency over time and between different contexts; however, little is known about the environmental factors shaping personality development. Because contrasting personalities are maintained with evolution, this lead to the widespread assumption that genes play a predominant role in personality. In many cases, personality traits are however also likely to be determined by individual experience, which is probably at least as important as genetics in shaping personality. The aim of this study was to assess how environmental variability (herein food predictability) impacts behavioral responses, particularly the shyness-boldness axis, one of the most widely shared animal personality trait. Here, we reared juvenile seabass (95 days old) from two divergent strains selected for feed deprivation tolerance under standard conditions for 40 days. Thereafter, we submitted them to two feeding treatments (Predictable versus Unpredictable) starting at 135 dph and lasting 60 days. Seabass reared under a predictable food supply (PFS) grew faster and were shyer than fish reared under an unpredictable food supply (UFS) ( i.e. they took more time to exit the refuge zone of a Z-maze; UFS: 132.47 ± 34.63 s; PFS: 336.79 ± 56.97 s) but their exploration tendency was similar. We also examined the behavioral responses of these fish facing a hypoxic challenge. Hypoxia tolerance results were consistent before and after the two feeding treatments. Our findings show the importance of early environmental experience as a driving force shaping boldness. In addition, we provide further evidence that predictable feeding time should be respected in studies assessing essential functions such as growth and behavior. Although personality traits are partially heritable, this study demonstrates the important influence of environmental conditions and life history on behavior. [ABSTRACT FROM AUTHOR]

The shy–bold continuum is both a fundamental aspect of human behavior and a relatively stable behavioral trait for many other species. Here we assessed whether shy individuals prefer familiar congeners, taking the European sea bass, a recently domesticated fish showing similar behavioral responses to wild fish, as a model to better understand the inter-individual variability in social behavior previously observed in this species. In the wild, the link between familiarity i . e ., the preference of fish for familiar congeners and boldness could be part of the mechanism underlying shoaling formation in fish. Thirty fish were individually tested in a device designed to assess the preference for a familiar vs . an unfamiliar congener on the basis of visual cues only. An open field test (OFT) with shelter was performed on the same fish 32 days later to assess the boldness of each individual. Variables of interest included the proportion of time spent in the shelter, border and center zone of the arena and variables of activity. Variables measured in OFT were collapsed into first principal component scores using Principal Components Analysis (PCA) which allowed characterizing a shy-bold continuum. Time spent near the familiar congener was negatively correlated with boldness i . e ., shy individuals spent most of the time near the familiar congener. We discuss the relevance of these findings to the understanding of the behavior of European sea bass and suggest that the link between familiarity and shyness is a general aspect of both animal and human behavior. [ABSTRACT FROM AUTHOR]

Recent years have seen a growth of interest in the consistent differences in individual behaviour over time and contexts constituting the so-called “individual coping styles”. An understanding of this inter-individual variation is essential to improve our knowledge of the adaptive value of behaviour. Coping styles may have implications in diverse fields, so the development of appropriate screening methods for each species appears to be the most effective way to extend our knowledge and to incorporate behavioural responses into selection-based breeding programmes, to improve the domestication and welfare of farmed fish. We tested 30 juvenile seabass ( Dicentrarchus labrax ) at least twice in individual-based tests (feeding recovery in isolation, aggressiveness, exploration in a T-maze and net restraint) and group-based tests (risk-taking and hypoxia sorting), to assess coping style consistency in the short- and long-term and between tests. The results of individual-based tests were inconsistent over time and between tests in our setup: the time between repeat tests, learning and species-specific behavioural responses appeared to have a major impact. By contrast, the results of group-based tests, such as risk-taking and hypoxia sorting, appeared to be consistent (both in the short- and long-term). These tests therefore appeared to be the most relevant for the characterisation of coping style in European seabass. Furthermore, the results of these tests were also predictive of cortisol stress response. These tests are simple to perform and can be used to screen large numbers of fish, the first step in selection programmes including behavioural profiles. [ABSTRACT FROM AUTHOR]

Most studies carried out with seabass under self-feeding conditions report an intriguing social structure that is built around the device and the food dispenser with three coexisting triggering categories: high-triggering (HT), low-triggering (LT) and zero-triggering (ZT) fish. However, neither sex nor feeding motivation or hierarchy can explain the establishment of this specialization. We characterized the personality of seabass with the commonly used restraint and open field tests and assessed the link between personality traits and individual triggering activity towards the self-feeder apparatus. We found no differences between triggering categories during the restraint test but high triggering fish were characterized as shyer than low- and zero-triggering fish during the open field test. Triggering activity was negatively correlated with exploratory capacities and boldness. This experiment provides for the first time evidence that high triggering status in seabass is correlated with personality traits, which could partly explain the social structure that builds around a self-feeder device. [ABSTRACT FROM AUTHOR]

Abstract: Behavioural studies comparing hatchery and wild-caught fish are useful to improve selection for aquaculture and restocking programmes. We examined swimming behaviour characteristics in wild captured and domesticated sea bass juveniles before and after eliciting a startle response at 8 different ages and always on naive individuals. We specifically investigated whether domestication impacts juvenile sea bass behaviour and whether the first months of captivity induce behavioural modifications in wild juveniles. An apparatus was designed to mimic a predator attack by presenting a sudden visual and mechanical stimuli simultaneously in 8 arenas where single individuals were placed and video recorded. The reactivity response was evaluated and different swimming variables including angular velocity, total distance travelled, mean velocity, immobility and distance from stimulus point were analysed from videos taken 5min before stimulus actuation, 5 and 15min after. Otolith readings showed that wild and domesticated juveniles were of similar age (∼55 days at the start of the experiment and ∼125 at the end of experiment). There were consistent behavioural differences (e.g. higher angular velocity and distance from stimulus point in wild fish) demonstrating that domestication reduces flight response behaviour. There were also similarities between both fish origins (similar response to stimulus actuation: decrease of total distance travelled and mean velocity, increase of angular velocity and immobility). A decrease over time in reactivity and variability in swimming responses among fish of both origins showed that captivity only does not fully explain wild fish behaviour changes and ontogenic modifications are likely interplaying. [Copyright &y& Elsevier]

Stress modifies energy allocation in fishes by redirecting energy from growth and reproduction to coping mechanisms. However, these adjustments become inappropriate when the challenge consists of sustained or repeated stressors, with the animal entering a maladaptive state. Capacities to cope with additional threats are then altered and compromise survival. The characterization of the responses to chronic stress in fishes helps better understanding the physiological limits in an aquaculture or ecological context. Here, we investigate the coping capacities of European sea bass to multiple and diverse stressors applied over a 3-weeks period. Multiple behavioural (group dispersion and swimming activity) and physiological responses (blood cortisol, osmoregulatory mechanisms, stress-related gene expression, etc.) were evaluated in resting fish or in fish exposed to additional challenges. Resilience to the chronic stress protocol was evaluated 4 months after the end of the chronic stress. Chronically stressed individuals showed reduced growth, lower cortisol response, increased chloride and sodium concentration in the plasma and modified gill gene expression translating osmoregulatory dysfunctions. Chronic stress had no significant effect on plasmatic calcium, lysozyme concentration and osmotic pressure. Increased thigmotaxic behaviour was observed in a new environment behavioural test. Four months after the chronic stress, no significant difference was observed in growth performances and in plasma parameters. Altogether, gills and more generally osmoregulatory functions were found to be the most sensitive to the chronic stress, while only limited changes in growth, activity of the HPI axis, immunity and swimming behaviour were observed when assessed individually. This work demonstrates the necessity of using multiple and diverse endpoints related to different functions to properly assess health and welfare in fishes. • Stress load following a chronic stress protocol was assessed in European sea bass • Our broad approach shows that osmoregulatory functions are the most sensitive • Measures taken individually can be misleading when evaluating welfare in aquaculture • Multiple endpoints are needed to properly assess health and welfare in aquaculture [ABSTRACT FROM AUTHOR]

• Groups of fish were exposed to acute stressors (Hypoxia, Hyperoxia, High ammonia). • Behavior was recorded both during stress condition and following stress. • All stress conditions induce a decrease in activity, thigmotaxis and group cohesion. • Novel tank diving test was validated for welfare assessment in European sea bass. • Activity, thigmotaxis and group cohesion are sensitive welfare indicators. In aquaculture, fish are exposed to unavoidable stressors that can be detrimental for their health and welfare. However, welfare in farmed fish can be difficult to assess, and, so far, no standardized test has been universally accepted as a welfare indicator. This work contributes to the establishment of behavioural welfare indicators in a marine teleost in response to different water quality acute stressors. Groups of ten fish were exposed to high Total Ammonia Nitrogen concentration (High TAN, 18 mg.L-1), Hyperoxia (200 % O 2 saturation), Hypoxia (20 % O 2 saturation), or control water quality (100% O 2 saturation and TAN < 2.5 mg.L-1) over 1 hour. Fish were then transferred in a novel environment for a group behaviour test under the same water quality conditions over 2 hours. Videos were recorded to assess thigmotaxis, activity and group cohesion. After this challenge, plasma cortisol concentration was measured in a subsample, while individual behavioural response was measured in the other fish using novel tank diving test. Prior to this study, the novel tank diving test was validated as a behavioural challenge indicative of anxiety state, by using nicotine as anxiolytic drug. Overall, all stress conditions induced a decrease in activity and thigmotaxis and changes in group cohesion while only fish exposed to Hypoxia and High TAN conditions displayed elevated plasma cortisol concentrations. In post -stress condition, activity was still affected but normal behaviour was recovered within the 25 minutes of the test duration. Our work suggests that the activity, thigmotaxis and group cohesion are good behavioural indicators of exposure to degraded water quality, and could be used as standardized measures to assess fish welfare. [ABSTRACT FROM AUTHOR]

• Reactive fish showed a slower stress recovery after acute confinement stress. • Serotonin turnover ratio was affected by acute confinement stress. • A positive correlation was shown between plasma cortisol and serotonin turnover ratio. Individual stress coping style (reactive, intermediate and proactive) was determined in 3 groups of 120 pit tagged European seabass using the hypoxia avoidance test. The same three groups (no change in social composition) were then reared according to the standards recommended for this species. Then, 127 days later, individuals initially characterized as reactive, intermediate or proactive were submitted to an acute confinement stress for 30 min. Blood samples were taken to measure plasma cortisol levels 30 min (Stress30) or 150 min (Stress150) after the end of the confinement stress. Individuals were then sacrificed to sample the telencephalon in order to measure the main monoamines and their catabolites (at Stress30 only). Individuals from Stress150 were sampled for whole brain for a transcriptomic analysis. The main results showed that reactive individuals had a lower body mass than intermediate individuals which did not differ from proactive individuals. The physiological cortisol response did not differ between coping style at Stress30 but at Stress150 when intermediate and proactive individuals had recovered pre stress levels, reactive individuals showed a significant higher level illustrating a modulation of stress recovery by coping style. Serotonin turnover ratio was higher in proactive and reactive individuals compared to intermediate individuals and a significant positive correlation was observed with cortisol levels whatever the coping style. Further, the confinement stress led to a general increase in the serotonin turnover comparable between coping styles. Stress150 had a significant effect on target mRNA copy number (Gapdh mRNA copy number decreased while ifrd1 mRNA copy number increased) and such changes tended to depend upon coping style. [ABSTRACT FROM AUTHOR]