Can we predict personality in fish? Searching for consistency over time and across contexts

Effects of Personality and Behavioral Syndromes on Competition for Social Hierarchical Status in Anemonefish Amphiprion clarkii

In this study, the behavioral ethogram of Amphiprion clarkii during the growth phase prior to sexual differentiation was summarized based on behavioral observations in three social environments. These behaviors can be classified into four categories: in addition to normal behaviors, the other three categories of behaviors-threatening, agonistic, and appeasing behaviors-represent different intentions in interactions with other individuals. Subsequently, the personalities of each individual were assessed by testing their reactions to intruders. These individuals mainly exhibited two distinct personality types: bold-aggressive and shy-submissive. In pairing experiments, the interactive behaviors of the anemonefish were observed in pairing combinations of different body sizes and personalities. The impact of personality on the establishment of a stable social hierarchy was confirmed by significant differences in the success rates of different pairing combinations, with the frequency of appeasing behaviors being the main factor influencing the success rate. Our results suggested that in natural waters, when juvenile individuals migrate among host anemones, shy-submissive individuals are more likely to be accepted due to their appeasing behaviors towards larger individuals, thus avoiding the risk of being attacked and bitten, and benefiting the survival of the individual. Conversely, bold-aggressive individuals are more likely to be driven away to another host anemone due to their unwillingness to settle for a lower-ranked status, thereby contributing to population dispersal and increasing opportunities for gene exchange between populations.

Switch from fight-flight to freeze-hide: The impacts of severe stress and brain serotonin on behavioral adaptations in flatfish

Animals often experience changes in their environment that can be perceived as stressful. Previous evidence indicates that different individuals may have distinct stress responses. The role of serotonin (5-HT) in stress adaptation is well established, but its relationship with different defense strategies and the persistence of physiological and behavioral responses in different individuals during repeated acute stress remain unclear. In this study, using olive flounder (Paralichthys olivaceus) as a model, we analyzed the relationship between boldness and neurotransmitter 5-HT activity. We found that 5-HT suppression with 5-HT synthesis inhibitor p-chlorophenylalanine (pCPA) and 5-HT receptor subtype 1A (5-HT1A) antagonist WAY-100635 increased their oxygen consumption rates and the boldness of shy individuals. We determined the metabolic and behavioral changes in bold and shy individuals to repeated acute stress. The results suggest that bold individuals switch on passive "energy-saving" personality by changing their defense behavior from "fight-flight" to "freeze-hide" during a threat encounter, which manifests high behavioral plasticity. Both behavioral types decreased their spontaneous activity levels, which were also strengthened by limiting metabolic rate. Interestingly, treatment with pCPA and WAY-100635 before stress procedure attenuated stress and increased the boldness across diverse behavioral types. This study provides the initial empirical evidence of how perception of stress impacts both individual defense behavior and personality in this species. These findings can enhance our comprehension of individual variability and behavioral plasticity in animals, thereby improving our ability to develop effective adaptive management strategies.

Trait sensitivity to stress and cognitive bias processes in fish: A brief overview

Like other animals, fish have unique personalities that can affect their cognition and responses to environmental stressors. These individual personality differences are often referred to as "behavioural syndromes" or "stress coping styles" and can include personality traits such as boldness, shyness, aggression, exploration, locomotor activity, and sociability. For example, bolder or proactive fish may be more likely to take risks and present lower hypothalamo-pituitary-adrenal/interrenal axis reactivity as compared to shy or reactive individuals. Likewise, learning and memory differ between fish personalities. Reactive or shy individuals tend to have faster learning and better association recall with aversive stimuli, while proactive or bold individuals tend to learn more quickly when presented with appetitive incentives. However, the influence of personality on cognitive processes other than cognitive achievement in fish has been scarcely explored. Cognitive bias tests have been employed to investigate the interplay between emotion and cognition in both humans and animals. Fish present cognitive bias processes (CBP) in which fish's interpretation of stimuli could be influenced by its current emotional state and open to environmental modulation. However, no study in fish has explored whether CBP, like in other species, can be interpreted as long-lasting traits and whether other individual characteristics may explain its variation. We hold the perspective that CBP could serve as a vulnerability factor for the onset, persistence, and recurrence of stress-related disorders. Therefore, studying fish's CBP as a state or trait and its interactions with individual variations may be valuable in future efforts to enhance our understanding of anxiety and stress neurobiology in animal models and humans.

Fish personality: meta-theoretical issues, personality dimensions, and applications to neuroscience and psychopathology

While the field of personality neuroscience has extensively focused on humans and, in a few cases, primates and rodents, a wide range of research on fish personality has emerged in the last decades. This research is focused mainly on the ecological and evolutionary causes of individual differences and also aimed less extensively at proximal mechanisms (e.g., neurochemistry or genetics). We argue that, if consistent and intentional work is made to solve some of the meta-theoretical issues of personality research both on fish and mammals, fish personality research can lead to important advances in personality neuroscience as a whole. The five dimensions of personality in fish (shyness-boldness, exploration-avoidance, activity, aggressiveness, and sociability) need to be translated into models that explicitly recognize the impacts of personality in psychopathology, synergizing research on fish as model organisms in experimental psychopathology, personality neuroscience, and ecological-ethological approaches to the evolutionary underpinnings of personality to produce a powerful framework to understand individual differences.

Enhancement of Soybean Meal Alters Gut Microbiome and Influences Behavior of Farmed Atlantic Salmon (Salmo salar)

Atlantic salmon (Salmo salar) is one of the worlds most domesticated fish. As production volumes increase, access to high quality and sustainable protein sources for formulated feeds of this carnivorous fish is required. Soybean meal (SBM) and soy-derived proteins are the dominant protein sources in commercial aquafeeds due to their low-cost, availability and favorable amino acid profile. However, for Atlantic salmon, the inclusion of soybean meal (SBM), and soy protein concentrate (SPC) in certain combinations can impact gut health, which has consequences for immunity and welfare, limiting the use of soy products in salmonid feeds. This study sought to address this challenge by evaluating two gut health-targeted enhancements of SBM for inclusion in freshwater phase salmon diets: enzyme pre-treatment (ETS), and addition of fructose oligosaccharide (USP). These were compared with untreated soybean meal (US) and fish meal (FM). This study took a multi-disciplinary approach, investigating the effect on growth performance, gut microbiome, and behaviors relevant to welfare in aquaculture. This study suggests that both enhancements of SBM provide benefits for growth performance compared with conventional SBM. Both SBM treatments altered fish gut microbiomes and in the case of ETS, increased the presence of the lactic acid bacteria Enterococcus. For the first time, the effects of marine protein sources and plant protein sources on the coping style of salmon were demonstrated. Fish fed SBM showed a tendency for more reactive behavior compared with those fed the FM-based control. All fish had a similar low response to elicited stress, although ETS-fed fish responded more actively than US-fed fish for a single swimming measure. Furthermore, SBM-fed fish displayed lower repeatability of behavior, which may indicate diminished welfare for intensively farmed fish. The implications of these findings for commercial salmonid aquaculture are discussed.

Disparate behavioral types in wild and reared juveniles of gilthead seabream

Fish differ consistently in behavior within the same species and population, reflecting distinct behavioral types (BTs). Comparing the behavior of wild and reared individuals provides an excellent opportunity to delve into the ecological and evolutionary consequences of BTs. In this work, we evaluated the behavioral variation of wild and reared juvenile gilthead seabreams, Sparus aurata, a highly relevant species for aquaculture and fisheries. We quantified behavioral variation along the five major axes of fish behavioral traits (exploration-avoidance, aggressiveness, sociability, shyness-boldness, and activity) using standardized behavioral tests and a deep learning tracking algorithm for behavioral annotation. Results revealed significant repeatability in all five behavior traits, suggesting high consistency of individual behavioral variation across the different axes in this species. We found reared fish to be more aggressive, social and active compared to their wild conspecifics. Reared individuals also presented less variance in their aggressiveness, lacking very aggressive and very tame individuals. Phenotypic correlation decomposition between behavioral types revealed two different behavioral syndromes: exploration-sociability and exploration-activity. Our work establishes the first baseline of repeatability scores in wild and reared gilthead seabreams, providing novel insight into the behavior of this important commercial species with implications for fisheries and aquaculture.

Identifying knowledge gaps in understanding the effects of selective serotonin reuptake inhibitors (SSRIs) on fish behaviour

Selective serotonin reuptake inhibitors (SSRIs) are a class of antidepressants increasingly prescribed to treat patients with clinical depression. As a result of the significant negative impact of the COVID-19 pandemic on the population's mental health, its consumption is expected to increase even more. The high consumption of these substances leads to their environmental dissemination, with evidence of their ability to compromise molecular, biochemical, physiological, and behavioural endpoints in non-target organisms. This study aimed to provide a critical review of the current knowledge regarding the effects of SSRI antidepressants on fish ecologically relevant behaviours and personality-dependent traits. A literature review shows limited data concerning the impact of fish personality on their responses to contaminants and how such responses could be influenced by SSRIs. This lack of information may be attributable to a lack of widely adopted standardized protocols for evaluating behavioural responses in fish. The existing studies examining the effects of SSRIs across various biological levels overlook the intra-specific variations in behaviour and physiology associated with different personality patterns or coping styles. Consequently, some effects may remain undetected, such as variations in coping styles and the capacity to handle environmental stressors. This oversight could potentially result in long-term effects with ecological implications. Data support the need for more studies to understand the impact of SSRIs on personality-dependent traits and how they may impair fitness-related behaviours. Given the considerable cross-species similarity in the personality dimensions, the collected data may allow new insights into the correlation between personality and animal fitness.

Exposure of zebrafish to an environmental mixture of persistent organic pollutants triggers an increase in anxiety-like syndrome but does not affect boldness in unexposed offspring

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants (POPs) that are present as complex mixtures in all environmental compartments, including aquatic ecosystems. However, little is known about the effects of such complex mixtures on teleost behaviour. In this study, zebrafish (Danio rerio) were chronically exposed to an environmentally relevant mixture (MIX) containing 22 PCB and 7 PBDE congeners through diet from 5 days post fertilization onwards. MIX-exposed F0 fish produced offspring (F1 and F2 generations) that were fed using plain food and grown until adulthood. In each generation, five behavioural traits (i.e. boldness, activity, sociality, exploration and anxiety) were evaluated by the mean of different experimental set-ups. Two distinct behavioural syndromes were identified: boldness, positively correlated to activity and exploration; and anxiety, associated with low sociality. F0 fish did not display any behavioural disruption resulting from POP exposure whereas F1 MIX fish were bolder than fish from other generations but did not differ significantly from F1 controls. F2 MIX fish displayed a higher anxiety syndrome than F2 controls. This is of particular importance since such behavioural changes in offspring generations may have persistent ecological consequences, may affect fitness and hence cause detrimental effects on wild fish populations exposed to POP mixtures.

Live fish learn to anticipate the movement of a fish-like robot. BIOINSPIRATION & BIOMIMETICS 2022;17:065007. [PMID: 36044889 DOI: 10.1088/1748-3190/ac8e3e]

The ability of an individual to predict the outcome of the actions of others and to change their own behavior adaptively is called anticipation. There are many examples from mammalian species-including humans-that show anticipatory abilities in a social context, however, it is not clear to what extent fishes can anticipate the actions of their interaction partners or what the underlying mechanisms are for that anticipation. To answer these questions, we let live guppies (Poecilia reticulata) interact repeatedly with an open-loop (noninteractive) biomimetic robot that has previously been shown to be an accepted conspecific. The robot always performed the same zigzag trajectory in the experimental tank that ended in one of the corners, giving the live fish the opportunity to learn both the location of the final destination as well as the specific turning movement of the robot over three consecutive trials. The live fish's reactions were categorized into a global anticipation, which we defined as relative time to reach the robot's final corner, and a local anticipation which was the relative time and location of the live fish's turns relative to robofish turns. As a proxy for global anticipation, we found that live fish in the last trial reached the robot's destination corner significantly earlier than the robot. Overall, more than 50% of all fish arrived at the destination before the robot. This is more than a random walk model would predict and significantly more compared to all other equidistant, yet unvisited, corners. As a proxy for local anticipation, we found fish change their turning behavior in response to the robot over the course of the trials. Initially, the fish would turn after the robot, which was reversed in the end, as they began to turn slightly before the robot in the final trial. Our results indicate that live fish are able to anticipate predictably behaving social partners both in regard to final movement locations as well as movement dynamics. Given that fish have been found to exhibit consistent behavioral differences, anticipation in fish could have evolved as a mechanism to adapt to different social interaction partners.

Investigating the physiological response and antibody concentration of gilthead sea bream (Sparus aurata) following Vibrio anguillarum vaccination depending on the stress coping style

Stress coping styles (SCSs) are defined as coherent sets of individual physiological and behavioral differences in stress response consistent across time and context and are described in a wide range of taxa, including fishes. These differences in behavior and physiology are of great interest because they may have direct implications on animal health, welfare, and performance in farming systems, including aquaculture. In this study, the physiological responses of sea bream (Sparus aurata) from different SCSs following Vibrio anguillarum vaccination were monitored. Fish were first screened either bold or shy (proxy of proactive and reactive SCSs, respectively) using group risk-taking tests and were then injected with a vaccine against V. anguillarum. Following vaccination, the fish were implanted with an accelerometer tag to monitor their swimming activity (proxy of energy expenditure), and blood sampling was carried out to measure health and welfare parameters (e.g., cortisol, glucose, hemoglobin) and aspecific immunity (e.g., protease, total proteins). In addition, blood was also collected at three different sampling times to screen antibody levels and, thus, to evaluate the efficiency of the vaccine. Following vaccination, bold fish displayed lower swimming activity values, indicative of lower energy expenditure, and also displayed higher levels of hematocrit, total proteins, and lysozyme in the plasma than the shy ones, which could be indicative of better health/welfare status and greater aspecific immunity. Finally, the V. anguillarum vaccination appeared to be more efficient in bold fish since the number of total antibodies was found higher than in shy fish 1 month after vaccination. Such results could help improve both health/welfare and productivity of farmed sea breams by selecting more robust fish, better adapted to farming conditions.

Variation in nest building, aggression, learning, and steroid hormone levels in Betta splendens

Individuals within a population present behavioral responses that vary according to intrinsic and extrinsic factors such as ontogenetic phase, nutritional status, reproductive stage, and previous experiences. These differences can be explained by endogenous changes, such as hormone release, that can modulate reproductive behaviors, stress response, and cognitive processes. In order to investigate the relationship between behavior and hormonal levels in the fighting fish Betta splendens, the present study characterized nest building, aggressive behavior, learning of a task, and levels of cortisol and 11-ketotestosterone (11-KT) in 86 male Fighting fish. At the beginning of the experiment (days 1-4), fish were characterized as nest builders, intermediate builders, or non-builders. They were then sequentially tested for aggression (days 7-8), learning performance (days 11-21), and circulating hormone levels (day 23). Nest builders showed the lowest hormonal levels at the end of the experiment and low aggressiveness; Intermediate builders presented low cortisol, but high KT levels and best learned the task; Non-builders were the most aggressive animals with higher cortisol levels (at day 23). Our data suggest that in B. splendens, aggressive behavior and learning performance are related to the relative investment in reproduction and variation in circulating levels of corticosteroids and androgens.

Differential Branchial Response of Low Salinity Challenge Induced Prolactin in Active and Passive Coping Style Olive Flounder

Stress coping styles are very common in fish, and investigations into this area can greatly improve fish welfare and promote the sustainable development of aquaculture. Although most studies have focused on the behavioral and physiological differences of these fishes, the endocrine response of different coping styles fish when undergoing salinity challenge is still unclear. We examined the physiological response in olive flounder with active coping (AC) style and passive coping (PC) style after transferred from seawater (SW) to freshwater for 0, 2, 5, 8, and 14 days. The results showed that: 1) the plasma prolactin level of FW-acclimated AC flounder was substantially higher than that of FW-acclimated PC flounder at 5, 8, and 14 days, and the branchial gene expression of prolactin receptor (PRLR) in AC flounder was slightly higher than PC flounder after transfer. While there was no remarkable difference observed in cortisol (COR) levels between AC and PC flounder. After transfer, glucocorticoid receptor (GR) expression in AC flounder was significantly higher compared with PC flounder at 8 days. 2) Branchial NKA-IR ionocytes numbers were reduced in PC flounder after transfer, while ionocytes number remain stable in AC flounder. 3) The branchial stem cell transcription factor foxi1 gene expression of AC flounder was significantly higher than PC flounder at 2, 5, and 14 days after transfer, while branchial stem cell transcription factor p63 gene expression of FW-acclimated AC flounder was only substantially higher than that of PC flounder at 5 days. 4) As an apoptosis upstream initiator, the branchial gene expression of caspase-9 in PC flounder was considerably higher than in AC flounder after transfer at 8 days. This study revealed that olive flounder with active and passive coping styles have different endocrine coping strategies after facing the low-salinity challenge. AC flounder adopt an active endocrine strategy by increasing ionocyte differentiation and prolactin secretion significantly. In contrast, PC flounder employ a passive strategy of reducing ionocytes differentiation and retaining prolactin content at a low level to reduce branchial ionocytes number.

Personality as a Predictor of Time-Activity Budget in Lion-Tailed Macaques (Macaca silenus)

Simple Summary

Time-activity budgets describe how animals divide their day into various behaviours and activities, e.g., time spent foraging or resting. Activity budgets can serve as crucial indicators of energy intake and expenditure, providing better knowledge of a species’ lifestyle. The conventional trend has been to explore group-level time-activity budgets; however, individuals may also vary in their time-activity budgets (e.g., one individual foraging more than another), with the influencing mechanisms still poorly understood. We propose that animal personality, a behavioural and cognitive profile that makes one individual different from another, may explain why individuals vary in their time-activity budgets. We used a multi-method approach comprised of behavioural observations and experiments to assess the personality traits of lion-tailed macaques. The observed traits were used to predict individual time-activity budgets, broadly categorised into food-related, active, and resting behaviours. We then discuss the significance of this novel approach in light of lion-tailed macaque ecology, conservation, and welfare.

Abstract

Time-activity budget, i.e., how a population or an individual divides their day into various behaviours and activities, is an important ecological aspect. Existing research primarily focused on group-level time-activity budgets, while individual variations have only been reported recently. However, little is known about how consistent inter-individual differences or personalities influence time-activity budgets. We examined the personalities of lion-tailed macaques (Macaca silenus) and investigated their influence on individual time-activity budgets. The resulting personality traits, namely persistence, sociability, affiliation, and anxiety, were used to predict the three broad categories of the time-activity budget—food-related, active, and resting behaviours. We found that persistence and sociability positively predicted the time spent being active. Food-related behaviours were positively predicted by persistence, while anxiety was found to influence them negatively. The time spent resting was negatively predicted by persistence. We did not find an effect of affiliation on the time-activity budgets. We discuss these findings in light of the ecology of lion-tailed macaques. Our study highlights the importance of a novel approach that uses animal personality traits as predictors of individual time-activity budgets and offers insights regarding the use of personality assessments in conservation and welfare activities.

Transcriptomic profiles of consistent risk-taking behaviour across time and contexts in European sea bass

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.

Measuring inter-individual differences in behavioural types of gilthead seabreams in the laboratory using deep learning

Deep learning allows us to automatize the acquisition of large amounts of behavioural animal data with applications for fisheries and aquaculture. In this work, we have trained an image-based deep learning algorithm, the Faster R-CNN (Faster region-based convolutional neural network), to automatically detect and track the gilthead seabream, Sparus aurata, to search for individual differences in behaviour. We collected videos using a novel Raspberry Pi high throughput recording system attached to individual experimental behavioural arenas. From the continuous recording during behavioural assays, we acquired and labelled a total of 14,000 images and used them, along with data augmentation techniques, to train the network. Then, we evaluated the performance of our network at different training levels, increasing the number of images and applying data augmentation. For every validation step, we processed more than 52,000 images, with and without the presence of the gilthead seabream, in normal and altered (i.e., after the introduction of a non-familiar object to test for explorative behaviour) behavioural arenas. The final and best version of the neural network, trained with all the images and with data augmentation, reached an accuracy of 92,79% ± 6.78% [89.24-96.34] of correct classification and 10.25 ± 61.59 pixels [6.59-13.91] of fish positioning error. Our recording system based on a Raspberry Pi and a trained convolutional neural network provides a valuable non-invasive tool to automatically track fish movements in experimental arenas and, using the trajectories obtained during behavioural tests, to assay behavioural types.

Cohabitation With Atlantic Salmon (Salmo salar) Affects Brain Neuromodulators But Not Welfare Indicators in Lumpfish (Cyclopterus lumpus)

Lumpfish are utilized to combat ectoparasitic epidemics in salmon farming. Research gaps on both cleaning behavior and client preferences in a natural environment, emphasizes the need to investigate the physiological impacts on lumpfish during cohabitation with piscivorous Atlantic salmon. Lumpfish (39.9 g, S.D ± 8.98) were arranged in duplicate tanks (n = 40 per treatment) and exposed to Live Atlantic salmon (245.7 g, S.D ± 25.05), salmon Olfaction or lifelike salmon Models for 6 weeks. Growth and health scores were measured every second week. In addition, the final sampling included measurements of neuromodulators, body color, and plasma cortisol. A stimulation and suppression test of the hypothalamic-pituitary-interrenal (HPI) axis was used for chronic stress assessment. Results showed that growth, health scores, and body color remained unaffected by treatments. Significant reductions in levels of brain dopamine and norepinephrine were observed in Live compared to Control. Plasma cortisol was low in all treatments, while the stimulation and suppression test of the HPI axis revealed no indications of chronic stress. This study presents novel findings on the impact on neuromodulators from Atlantic salmon interaction in the lumpfish brain. We argue that the downregulation of dopamine and norepinephrine indicate plastic adjustments to cohabitation with no negative effect on the species. This is in accordance with no observed deviations in welfare measurements, including growth, health scores, body color, and stress. We conclude that exposure to salmon or salmon cues did not impact the welfare of the species in our laboratory setup, and that neuromodulators are affected by heterospecific interaction.

Covariation among behavioral traits and hatching time in zebrafish

Individuals of the same population differ in several ways. For instance, in fish populations, individuals who hatch earlier show more active behavior and are more explorative than those that hatch later, which is a characteristic of the behavioral personality type. One of the aspects relevant to this theory is the consistency of behavioral differences between contexts and over time. Thus, the present study evaluated the relationship between hatching time and behavioral consistency in two ontogenetic stages: juvenile and adult, and different contexts in zebrafish (Danio rerio). For this, the animals were separated according to hatching time into early-hatching (EH) and late-hatching (LH) fish and tested in an anxiety-like context (black-white paradigm) at the 30th-day post fertilization (dpf) and the 120th dpf. The animals were also tested in a novel tank paradigm and novel object paradigm to access explorativeness and boldness, respectively. In the black-white test, EH animals presented shorter latency to enter the white area and stayed longer in the black area than LH animals. The EH individuals were more explorative and bold in the novel tank and novel object tests and showed less anxiety-like behavior than the LH. In general, the results obtained suggest that hatching time may indicate consistent differences for zebrafish behavioral profiles.

Cross-Context Responses to Novelty in Rural and Urban Small Mammals

The Anthropocene is the era of urbanization. The accelerating expansion of cities occurs at the expense of natural reservoirs of biodiversity and presents animals with challenges for which their evolutionary past might not have prepared them. Cognitive and behavioral adjustments to novelty could promote animals’ persistence under these altered conditions. We investigated the structure of, and covariance between, different aspects of responses to novelty in rural and urban small mammals of two non-commensal rodent species. We ran replicated experiments testing responses to three novelty types (object, food, or space) of 47 individual common voles (Microtus arvalis) and 41 individual striped field mice (Apodemus agrarius). We found partial support for the hypothesis that responses to novelty are structured, clustering (i) speed of responses, (ii) intensity of responses, and (iii) responses to food into separate dimensions. Rural and urban small mammals did not differ in most responses to novelty, suggesting that urban habitats do not reduce neophobia in these species. Further studies investigating whether comparable response patters are found throughout different stages of colonization, and along synurbanization processes of different duration, will help illuminate the dynamics of animals’ cognitive adjustments to urban life.

Density influences the heritability and genetic correlations of fish behaviour under trawling-associated selection

Fishing-associated selection is one of the most important human-induced evolutionary pressures for natural populations. However, it is unclear whether fishing leads to heritable phenotypic changes in the targeted populations, as the heritability and genetic correlations of traits potentially under selection have received little attention. In addition, phenotypic changes could arise from fishing-associated environmental effects, such as reductions in population density. Using fish reared at baseline and reduced group density and repeatedly harvested by simulated trawling, we show that trawling can induce direct selection on fish social behaviour. As sociability has significant heritability and is also genetically correlated with activity and exploration, trawling has the potential to induce both direct selection and indirect selection on a variety of fish behaviours, potentially leading to evolution over time. However, while trawling selection was consistent between density conditions, the heritability and genetic correlations of behaviours changed according to the population density. Fishing-associated environmental effects can thus modify the evolutionary potential of fish behaviour, revealing the need to use a more integrative approach to address the evolutionary consequences of fishing.

Hydropower-induced selection of behavioural traits in Atlantic salmon (Salmo salar)

Renewable energy projects such as hydropower facilities contribute towards meeting the world`s growing energy demands and urgent need for mitigating climate change. However, such infrastructure has the potential to substantially alter the environment which, in turn, can induce new challenges related to for instance fish migration conditions. As a consequence, local adaptations related to pre-development migration conditions may be affected for influenced populations. To explore selection regimes operating at a river hydropower plant, we monitored Atlantic salmon smolt individuals during their seaward migration. When passing the hydropower plant, the smolts chose between a surface fish passage or a submerged turbine intake. Smolts were scored for behavioural type (basal locomotor activity, net restrain (a measure of escape responses) and willingness to leave a familiar environment) prior to their migration choice, and we found that smolts with high basal activity had higher probability of using the fish passage than the turbine intake. In addition, migration route choice was a partly consistent trait in that fish that had previously passed a hydroelectric facility by using a fish passage rather than the turbine intake were significantly more likely to use it again when faced with the same choice. Higher mortality among turbine migrants could potentially reduce or eliminate particular behaviour types within populations- and the corresponding population genetic diversity that is essential to cope with future environmental challenges.

Diel rhythm of urotensin I mRNA expression and its involvement in the locomotor activity and appetite regulation in olive flounder Paralichthys olivaceus

Urotensin I (UI), a member of the corticotropin-releasing hormone family of peptides, regulates a diverse array of physiological functions, including appetite regulation, defensive behavior and stress response. In this study, firstly, the tissue-specific distribution of UI mRNA in olive flounder (Paralichthys olivaceus) was characterized and we found that UI mRNA was highly expressed in caudal neurosecretory system (CNSS) tissue. Secondly, alignment analysis found that a conserved cAMP response binding (CREB) site and a TATA element were located in the proximal promoter of UI gene. In addition, treatment of forskolin activatated cAMP-CREB pathway and induced the up-regulation of UI mRNA in cultured CNSS, suggesting the role of CREB in regulating the UI mRNA expression. Furthermore, plasma UI concentration and UI mRNA in CNSS showed obvious daily rhythm, with higher values in the daytime while lower values in the nighttime. Thirdly, using bold personality (BP) and shy personality (SP) flounder as an animal model, we found that flounder exhibited significantly higher locomotor activity in the nighttime than in the daytime (P < 0.001), and BP flounder showed significantly higher locomotor activity (P < 0.001) compared with SP flounder both in the daytime and nighttime. Analysis of feeding behavior revealed that BP flounder showed a shorter latency to feed and more attacks to prey. Furthermore, the qPCR and immunohistochemistry results showed that BP flounder expressed significantly lower level of UI mRNA and protein in CNSS tissue. Collectively, our study suggested that the UI plays an important role in locomotor activity and appetite regulation, which provides a basis for understanding the mechanism of defensive behavior and animal personality in flounder.

The weakly electric fish, Apteronotus albifrons, actively avoids experimentally induced hypoxia

Anthropogenic environmental degradation has led to an increase in the frequency and prevalence of aquatic hypoxia (low dissolved oxygen concentration, DO), which may affect habitat quality for water-breathing fishes. The weakly electric black ghost knifefish, Apteronotus albifrons, is typically found in well-oxygenated freshwater habitats in South America. Using a shuttle-box design, we exposed juvenile A. albifrons to a stepwise decline in DO from normoxia (> 95% air saturation) to extreme hypoxia (10% air saturation) in one compartment and chronic normoxia in the other. On average, A. albifrons actively avoided the hypoxic compartment below 22% air saturation. Hypoxia avoidance was correlated with upregulated swimming activity. Following avoidance, fish regularly ventured back briefly into deep hypoxia. Hypoxia did not affect the frequency of their electric organ discharges. Our results show that A. albifrons is able to sense hypoxia at non-lethal levels and uses active avoidance to mitigate its adverse effects.

Do Females in a Unisexual-Bisexual Species Complex Differ in Their Behavioral Syndromes and Cortisol Production?

Simple Summary

In many species, including humans, individuals in a population have personalities: collections of correlated behaviors that are consistent across different environments (i.e., mating, eating). Personalities are affected by competitors for food or mates and the hormones produced by individuals). Competitors can include other individuals of the same species or closely related species. The all-female, Amazon molly is a hybrid species, and needs to coexist with one of its bisexual (males and females), parent species, to reproduce. One parent species of the Amazon molly is the sailfin molly. Female sailfin and Amazon mollies compete for access to males for mating and food which could affect the personalities of individuals of each species. We found that both species have similar personalities consisting of a correlation between exploration and activity. We did not detect a relationship between a stress response hormone, cortisol, and individual personality. However, the all-female Amazons had higher cortisol release rates than sailfins. Personalities may be similar due to genetic constraints that link these behaviors, and might benefit Amazons if this causes male sailfin mollies to mismate with them. However, the differences in cortisol release rates may be a useful mate identification cue for males to offset such mating mistakes.

Abstract

Studies of suites of correlated behavioral traits (i.e., behavioral syndromes) aid in understanding the adaptive importance of behavioral evolution. Behavioral syndromes may be evolutionarily constrained, preventing behaviors from evolving independently, or they may be an adaptive result of selection on the correlation itself. We tested these hypotheses by characterizing the behavioral syndromes in two sympatric, closely related species and testing for differences between the species. We studied the unisexual Amazon molly (Poecilia formosa) and one of its bisexual, parent species, the sailfin molly (P. latipinna). Sympatric female sailfin and Amazon mollies compete for mating which could affect the behavioral syndromes found in each species. We identified a behavioral syndrome between exploration and activity in both species that did not differ between species. Additionally, we explored the relationship between a stress response hormone, cortisol, and behavioral type, and did not detect a relationship. However, P. formosa differed from P. latipinna in their cortisol release rates. Behavioral syndromes may be constrained in this complex, aiding in mate acquisition for P. formosa by virtue of having a similar behavioral type to P. latipinna. The difference between the females in cortisol release rates may be a useful mate identification cue for males to offset higher mating mistakes associated with the similar behavioral types.

Selective disappearance does not underlie age-related changes in trait repeatability in red squirrels

Understanding the causes and consequences of repeatable among-individual differences in behavior (i.e., animal personality) is a major area of research in behavioral and evolutionary ecology. Recently, attention has turned to understanding the processes behind changes in repeatability through ontogeny because of their implications for populations. We evaluated the relative importance of selective disappearance (i.e., differential mortality), an among-individual mechanism, in generating age-related changes in the repeatability of aggression and activity in juvenile North American red squirrels (Tamiasciurus hudsonicus). We observed age-related decreases in the repeatability of aggression across ages, arising from lower among-individual variance. Although we found evidence for directional selection on aggressiveness, it was insufficient to erode among-individual variance. Thus, ontogenetic decreases in the repeatability of aggression do not appear to be due to selective disappearance. In contrast, the repeatability of activity was higher across ages due to higher among-individual variance in activity, but there was no support for selective disappearance based on activity. Taken together, our results suggest that age-related changes in trait repeatability in red squirrels are not the result of selective disappearance and instead may be the result of within-individual developmental processes, such as individual differences in developmental trajectories.

Analysis across diverse fish species highlights no conserved transcriptome signature for proactive behaviour

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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07317-z.

Rising to the challenge? Inter-individual variation of the androgen response to social interactions in cichlid fish

The Challenge Hypothesis (Wingfield et al. Am. Nat. 136, 829-846) aims to explain the complex relationship between androgens and social interactions. Despite its well acceptance in the behavioral endocrinology literature, several studies have failed to found an androgen response to staged social interactions. Possible reasons for these inconsistencies are the use of single sampling points that may miss the response peak, and the occurrence of inter-individual variability in the androgen response to social interactions. In this study we addressed these two possible confounding factors by characterizing the temporal pattern of the androgen response to social interactions in the African cichlid, Oreochromis mossambicus, and relating it to inter-individual variation in terms of the individual scope for androgen response (i.e. the difference between baseline and maximum physiological levels for each fish) and behavioral types. We found that the androgen response to territorial intrusions varies between individuals and is related to their scope for response. Individuals that have a lower scope for androgen response did not increase androgens after a territorial intrusion but were more aggressive and exploratory. In contrast males with a higher scope for response had fewer aggressive and exploratory behaviors and exhibited two peaks of KT, an early response 2-15 min after the interaction and a late response at 60-90 min post-interaction. Given that the pharmacological challenge of the Hypothalamic-Pituitary-Gonad axis only elicits the late response, we suggest that these two peaks may be regulated by different physiological mechanisms, with the early response being mediated by direct brain-gonad neural pathways. In summary, we suggest that determining the temporal pattern of the androgen response to social interactions and considering inter-individual variation may be the key to understanding the contradictory results of the Challenge Hypothesis.

Enriched environments enhance cognition, exploratory behaviour and brain physiological functions of Sparus aurata

Environmental enrichment is considered as a recommended tool to guarantee or improve the welfare of captive fish. This study demonstrates for the first time that structural environmental enrichment enhances cognition, exploratory behaviour and brain physiological functions of gilthead seabream (Sparus aurata). Seabream was reared in groups (n = 15) during 60 days under two different treatments: enriched tanks with plant-fibre ropes (EE) or bare/non-enriched tanks (NE). Fish were then exposed to a purpose-built maze for 1 h every second day in four trials. Analysis of video recordings showed that seabream under EE conditions presented higher overall exploratory behaviour, spatial orientation and learning capability compared to seabream from NE conditions. Results from brain monoamines analyses may suggest increased recent dopaminergic activity in telencephalon, known to be involved in learning processes; and increased serotonergic activity in cerebellum, involved in the coordination of balance, movements and orientation. In addition, EE-reared fish showed increased antioxidant activity in whole brain, with no apparent oxidative damage. Structural EE seemed to induce an hormetic response on juvenile seabream, improving their welfare status during captivity. Application of this kind of physical structure might be feasible at fish farms as a passive and non-invasive tool to improve welfare of intensively cultured seabream.

Zebrafish Danio rerio shows behavioural cross-context consistency at larval and juvenile stages but no consistency between stages

Coping style is defined as a set of individual physiological and behavioural characteristics that are consistent across time and context. In the zebrafish Danio rerio, as well as in many other animals, several covariations have been established among behavioural, physiological and molecular responses. Nonetheless, not many studies have addressed the consistency in behavioural responses over time starting at the larval stage. Therefore, this study aimed to improve the understanding of behavioural consistency across contexts and over time in zebrafish from the larval to juvenile stages. Two distinct experiments were conducted: a larval stage experiment (from 8 to 21 days post fertilization, dpf) and a juvenile stage experiment (from 21 to 60 dpf). On one hand, the larval experiment allows to focus on the transition between 8 and 21 dpf, marked by significant morphological changes related to the end of larval stage and initiation of metamorphosis. On the other hand, the juvenile experiment allows to properly cover the period extending from the end of larval stage to the juvenile stage (60 dpf), including metamorphosis which is itself completed around 45 dpf. Within each experiment, boldness was determined using a group risk-taking test to identify bold and shy individuals. A novel environment test was then performed at the same age to evaluate consistency across contexts. Groups of fish (either bold or shy) were bathed in an alizarin red S solution for later identification of their initially determined coping style to evaluate behavioural consistency over time. Fish were then reared under common garden conditions and challenged again with the same behavioural tests at a later age (21 and 60 dpf in the larval and juvenile experiments, respectively). Behavioural consistency was observed across contexts, with bold fish being more active and expressing higher thigmotaxis regardless of age. There was, however, little behavioural consistency over age, suggesting behavioural plasticity during development. Moreover, the use of alizarin red S to conduct this experiment provides new perspectives for the further study of the longitudinal evolution of various traits, including behaviour, over life stages in fish.

Contrasting neurochemical and behavioral profiles reflects stress coping styles but not stress responsiveness in farmed gilthead seabream (Sparus aurata)

In fish, as well as in other vertebrates, contrasting suites of physiological and behavioral traits, or coping styles, are often shown in response to stressors. However, the magnitude of the response (i.e. stress responsiveness) has been suggested to be independent of stress coping style. One central neurotransmitter that has been associated with both stress responsiveness and differences in stress coping styles is serotonin (5-hydroxytryptamine, 5-HT). In this study, we investigated to what extent stress responsiveness reflects differences in stress coping, and the potential involvement of the 5-HT system in mediating such differences in farmed Gilthead seabream. Initially, fish were classified as proactive or reactive based on their behavioural response to net restraint. Following 1.5 months, fish classified as proactive still showed a higher number of escape attempts and spent longer time escaping than those classified as reactive. These differences were reflected in a generally higher brain stem 5-HT concentration and a lower telencephalic 5-HT activity, i.e. the ratio of 5-hydroxyindoleacetic acid (5-HIAA) to 5-HT, in proactive fish. Independent of stress coping styles, stress responsiveness was reflected in elevated 5-HIAA concentrations and 5-HIAA/5-HT ratios in telencephalon and brain stem together with increased plasma cortisol concentrations at 0.5 and 2 h following the last net restraint. The current results show that 5-HT signaling can reflect different behavioural output to a challenge which are independent of neuroendocrine responses to stress and lend support to the hypothesis that stress coping styles can be independent of stress responsiveness.

Physiological responses during acute stress recovery depend on stress coping style in European sea bass, Dicentrarchus labrax

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.

Linking stress coping styles with brain mRNA abundance of selected transcripts for Senegalese sole (Solea senegalensis) juveniles

In fish, proactive and reactive individual stress copying styles (SCS) have been used to resolve variation in molecular expression data. Stress coping styles have been previously described in several stages of Solea senegalensis by validating for the species the use of standard behavioural screening tests. The present study aimed to link behavioural SCS tests with brain transcript abundance in early Senegalese sole juveniles in order to observe the natural variation in a molecular pathway in this species. A total of 50 juveniles were subjected to three individual behavioural (Restraining, New environment and Confinement) and one group (Risk-taking) screening tests. The fish were classified in SCS categories by applying a hierarchical cluster to the variable "Total activity" (the total activity time that the fish was moving in each individual test). Three categories were defined, proactive, intermediate and reactive sole. Six transcripts were chosen and tested, one related to basic metabolism (gapdh-2), three to feeding behaviour (per1, igf-Ia, pparß) and two to the stress response (crh-BP and hsp90aa) in 30 juveniles (10 individuals per SCS category) using rt-qPCR to observe differences in the abundance of those transcripts among SCS. Four transcripts were differentially expressed (DETs) among them. The transcript gapdh-2 showed up-regulation for proactive and intermediate SCS sole while reactive individuals showed down-regulation. Target mRNAs per1, igf-Ia and pparß, showed different levels of up-regulation for proactive and reactive fish while intermediates were highly down-regulated. Surprisingly no differences in stress related transcripts were observed. Correlations were found between variation in coping styles and variation in the abundance of mRNAs involved in important biological functions in Senegalese sole. These results are the first evidence of the relationship between the behavioural individual variation and the fluctuation in brain transcripts abundance in Senegalese sole.

Linking stocking densities and feeding strategies with social and individual stress responses on gilthead seabream (Sparus aurata)

Intensive aquaculture and poor management practices can cause stress and compromise welfare of farmed fish. This study aimed to assess the potential links between stocking densities and feeding methods with social and individual stress responses on juvenile seabream (Sparus aurata) through risk-taking and hypoxia tests. Seabream was first experimentally reared under two different densities: high (HD: 11-65 kg m^-3) and low (LD: 3-15 kg m^-3). After 120 days under these conditions, increment in fish weight was not affected by different stocking densities. HD seemed to induce a stronger schooling behavior on seabream juveniles seeking for the group safety during the risk test; while LD increased the mean number of movements per fish recorded and the time of first response. Additionally, HD conditions delayed the time of first response of proactive fish during hypoxia tests. Glucose levels were higher in reactive fish compared to proactive ones, being highly significant in fish reared at HD. In parallel, juvenile seabream was also experimentally reared for 106 days under two different feeding strategies: hand-feeding (HF) and self-demanding feeding (DF), which influenced fish growth and foraging behavior at group and individual level. HF method induced a positive effect on fish weight compared to DF systems. Time of first response during both hypoxia and risk-taking tests was shorter in HF fish than DF fish, and the mean number of movements per fish during risk-taking behavior tests was lower for DF fish compared to HF fish. No differences were found in glucose and cortisol concentrations between behavioral traits (proactive/reactive) and feeding strategies. Triggering actions of seabream in DF systems were also assessed, which seemed to be highly dependent on particular individuals and not related to proactive individuals. DF systems however reinforce the social hierarchy within the fish group, which might lead to a higher competitiveness for resources among fishes, increasing the social hierarchy, and therefore, the stress. The findings of this study provide valuable information to the industry for the management of fish stress and welfare under production conditions at social and individual level.

Behavioral and physiological responses to stocking density in sea bream (Sparus aurata): Do coping styles matter?

Stocking density is considered a stress factor for fish and is therefore one of the numerous concerns about fish welfare in an aquaculture context. Stress coping styles (SCS) are defined as a coherent set of individual physiological and behavioral differences in stress responses that are consistent across time and context and appear to be promising for improving fish welfare in aquaculture. The aim of the present study was to describe the physiological and zootechnical performances of gilthead sea bream (Sparus aurata) at different stocking densities (low density, LD: 15 kg/m³ and high density, HD: 30 kg/m³), depending on individual SCS. To do so, the fish SCS were first screened by measuring boldness (prior to the experiment). Three consecutive samplings were performed over the experiment to measure several blood parameters, including hematocrit (Hct), red blood cell count (RBCC), hemoglobin (Hb), cortisol, adrenalin, noradrenalin, glucose, lactate, and lysozyme, to infer the consequence of the SCS profile on the welfare condition in response to stocking density. Finally, swimming activity was recorded in a subsample of individuals (9 BOLD and 9 SHY individuals per density), and BOLD individuals displayed higher swimming activity than SHY ones at HD, while the opposite pattern was observed at LD. According to principal component analysis, physiological parameters are linked to the SCS profile, mostly at the beginning of the experiment, while density effects on physiology remain during the entire experiment duration. In conclusion, regarding all the variables observed, fish SCS appeared to be promising criteria to select the most adaptive individuals relating to rearing conditions and therefore improve welfare.

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.

The role of intraspecies variation in fish neurobehavioral and neuropharmacological phenotypes in aquatic models

Intraspecies variation is common in both clinical and animal research of various brain disorders. Relatively well-studied in mammals, intraspecies variation in aquatic fish models and its role in their behavioral and pharmacological responses remain poorly understood. Like humans and mammals, fishes show high variance of behavioral and drug-evoked responses, modulated both genetically and environmentally. The zebrafish (Danio rerio) has emerged as a particularly useful model organism tool to access neurobehavioral and drug-evoked responses. Here, we discuss recent findings and the role of the intraspecies variance in neurobehavioral, pharmacological and toxicological studies utilizing zebrafish and other fish models. We also critically evaluate common sources of intraspecies variation and outline potential strategies to improve data reproducibility and translatability.

Evidence that the stress hormone cortisol regulates biofilm formation differently among Flavobacterium columnare isolates

The impact of cortisol on Flavobacterium columnare biofilm formation was explored. Firstly, the dynamics of biofilm formation by one highly (HV) and one low virulent (LV) F. columnare isolate with and without the stress hormone cortisol under microfluidic flow conditions was characterized. This to confirm that F. columnare cells could form biofilm under cortisol supplementation, and to compare the temporal and structural differences between different treatment groups. One trial revealed that in both isolates cell aggregates resembling biofilms occurred within 7-h post-inoculation. Consequently, cell clusters were sloughed away, followed by a rebuilding of bacterial cell aggregates, suggestive for a high spreading capacity. While the HV isolate revealed cell aggregates formed upstream at all time-points, for the LV isolate this was only seen upon cortisol supplementation. Secondly, the transcriptional effect of genes (gldK, gldL, gldM, gldN, sprA, sprE, sprT, and porV) belonging to the Type IX secretion system involved in gliding motility was investigated in planktonic and biofilm cells of a HV and LV isolate to which no, a low (LD) or high (HD) dose of cortisol was added. Significantly lower expression of gliding genes gldK, gldL, gldM and gldN, and of protein secretion regulator porV was seen in the LV isolate planktonic cells supplemented with a HD-cortisol. The LV isolate biofilm cells treated with the HD-cortisol showed a significant upregulation of sprT, encoding mobile surface adhesion important in bacterial colonization. This is the first evidence for the co-regulatory effect of cortisol on biofilm formation and F. columnare gliding gene expression.

Proactive avoidance behaviour and pace-of-life syndrome in Atlantic salmon

Individuals in a fish population differ in key life-history traits such as growth rate and body size. This raises the question of whether such traits cluster along a fast-slow growth continuum according to a pace-of-life syndrome (POLS). Fish species like salmonids may develop a bimodal size distribution, providing an opportunity to study the relationships between individual growth and behavioural responsiveness. Here we test whether proactive characteristics (bold behaviour coupled with low post-stress cortisol production) are related to fast growth and developmental rate in Atlantic salmon, Salmo salar. Boldness was tested in a highly controlled two-tank hypoxia test were oxygen levels were gradually decreased in one of the tanks. All fish became inactive close to the bottom at 70% oxygen saturation. At 40% oxygen saturation level a fraction of the fish actively sought to avoid hypoxia. A proactive stress coping style was verified by lower cortisol response to a standardized stressor. Two distinct clusters of bimodal growth trajectories were identified, with fast growth and early smoltification in 80% of the total population. There was a higher frequency of proactive than reactive individuals in this fast-developing fraction of fish. The smolts were associated with higher post-stress plasma cortisol than parr, and the proactive smolts leaving hypoxia had significant lower post-stress cortisol than the stayers. The study demonstrated a link between a proactive coping and fast growth and developmental ratio and suggests that selection for domestic production traits promotes this trait cluster.

Reproductive success of a marine teleost was correlated with proactive and reactive stress-coping styles

The present study investigated the relationship between reproductive success and stress-coping styles in gilthead seabream Sparus aurata in captivity. To characterise stress-coping styles, a total of 22 breeders were submitted to three different individual-based tests, one group-based test and post-handling glucocorticoid quantification. To assess spawning participation, a microsatellite analysis was performed on a total of 2698 larvae, which allowed each offspring to be assigned unambiguously to a single parental couple. Overall, S. aurata showed defined proactive and reactive behavioural traits. Proactive breeders exhibited higher levels of activity and risk taking and lower glucocorticoid blood levels than reactive breeders. The stress-coping style traits were consistent over time and context (different tests). Breeders that contributed to a higher number of progeny exhibited proactive behaviours, while those showing low progeny contribution exhibited reactive behaviour. Therefore, breeders with a high proportion of progeny (> 20%) had significantly higher activity and risk taking and lower cortisol than breeders with low progeny contribution (< 20%). In addition, males were more proactive than females and males exhibited significantly higher activity, risk taking and lower cortisol than females. This study is the first to establish in S. aurata breeders: (a) a relationship between stress-coping styles and spawning success; (b) a relationship between stress-coping styles and gender; and (c) the existence of proactive and reactive traits at the adult stage.

Personality in the longsnout seahorse, Hippocampus reidi Ginsburg, 1933: Are males shyer than females?

Individual responses, particularly based on personality, can have important consequences for individual fitness, based upon success in exploring new habitats, feeding on novel foods, and aggressiveness in competitive interactions. We conducted laboratory experiments to analyze individual responses to different artificial conditions that could suit specific male and female personalities in the endangered seahorse, Hippocampus reidi. Our experiments with H. reidi evaluated individual responses to a new habitat, novel objects, level of inactivity and social interactions. We demonstrate that approximately half of the seahorses have a bold personality, readily inspecting new habitats and objects and sporadically presenting social approaches. The remaining shy individuals had high levels of inactivity and did not check novelties in their habitats. Although we expected that males would have shyer personalities when compared with females, due to their ecological role in the provision of parental care, we found no statistical difference between the sexes in terms of these aspects of personality. The similar frequency of both types of personality in males and females suggests that these features may be balanced and evolutionarily stable in the sampled population.

Understanding the Role of Environmental Enrichment in Zebrafish Neurobehavioral Models

Environmental stimuli are critical in preclinical research that utilizes laboratory animals to model human brain disorders. The main goal of environmental enrichment (EE) is to provide laboratory animals with better choice of activity and greater control over social and spatial stressors. Thus, in addition to being a useful experimental tool, EE becomes an important strategy for increasing the validity and reproducibility of preclinical data. Although zebrafish (Danio rerio) is rapidly becoming a promising new organism for neuroscience research, the role of EE in zebrafish central nervous system (CNS) models remains poorly understood. Here we discuss EE in preclinical studies using zebrafish and its influence on brain physiology and behavior. Improving our understanding of EE effects in this organism may enhance zebrafish data validity and reliability. Paralleling rodent EE data, mounting evidence suggests the growing importance of EE in zebrafish neurobehavioral models.

Repeatability and reliability of exploratory behavior in proactive and reactive zebrafish, Danio rerio

Behavioral responses to novel situations often vary and can belong to a suite of correlated behaviors. Characteristic behaviors of different personality types (e.g. stress coping styles) are generally consistent across contexts and time. Here, we compare the repeatability and reliability of exploratory behaviors between zebrafish strains selectively bred to display contrasting behavioral responses to stressors that represent the proactive-reactive axis. Specifically, we measure exploratory behavior of individual fish in an open field test over five weeks. We quantified the stationary time, average swimming speed and time spent by a fish in the center area. We found a number of strain differences for each behavioral measure. Stationary time was the most repeatable and reliable measure for assessing proactive-reactive behavioral differences. Reactive zebrafish generally showed the highest reliability and repeatability of exploratory behavior compared to proactive zebrafish and a separate wild caught strain. Given the increased interest in the evolutionary consequences and proximate mechanisms of consistent individual differences, it will be important to continue to investigate how different selective pressures may influence expression of stress coping styles and their effects on the consistency of an animal’s behavior.