Impacts of climate-related stressors on social group cohesion and individual sociability in fish.

Group-living in animals comes with a number of benefits associated with predator avoidance, foraging, and reproduction. A large proportion of fish species display grouping behaviour. Fish may also be particularly vulnerable to climate-related stressors including thermal variation, hypoxia, and acidification. As climate-related stressors are expected to increase in magnitude and frequency, any effects on fish behaviour may be increased and affect the ability of fish species to cope with changing conditions. Here we conduct a systematic review of the effects of temperature, hypoxia, and acidification on individual sociability and group cohesion in shoaling and schooling fishes. Searches of the published and grey literature were carried out, and studies were included or excluded based on selection criteria. Data from studies were then included in a meta-analysis to examine broad patterns of effects of climate-related stressors in the literature. Evidence was found for a reduction in group cohesion at low oxygen levels, which was stronger in smaller groups. While several studies reported effects of temperature and acidification, there was no consistent effect of either stressor on sociability or cohesion. There was some evidence that marine fishes are more strongly negatively affected by acidification compared with freshwater species, but results are similarly inconsistent and more studies are required. Additional studies of two or more stressors in combination are also needed, although one study found reduced sociability following exposure to acidification and high temperatures. Overall, there is some evidence that hypoxia, and potentially other climate-related environmental changes, impact sociability and group cohesion in fishes. This may reduce survival and adaptability in shoaling and schooling species and have further ecological implications for aquatic systems. However, this synthesis mainly highlights the need for more empirical studies examining the effects of climate-related factors on social behaviour in fishes.

Negative impacts of social isolation on behavior and neuronal functions are recovered after short-term social reintroduction in zebrafish.

Recently, social isolation measures were crucial to prevent the spread of the coronavirus pandemic. However, the lack of social interactions affected the population mental health and may have long-term consequences on behavior and brain functions. Here, we evaluated the behavioral, physiological, and molecular effects of a social isolation (SI) in adult zebrafish, and whether the animals recover such changes after their reintroduction to the social environment. Fish were submitted to 12 days of SI, and then reintroduced to social context (SR). Behavioral analyses to evaluate locomotion, anxiety-like and social-related behaviors were performed after SI protocol, and 3 and 6 days after SR. Cortisol and transcript levels from genes involved in neuronal homeostasis (c-fos, egr, bdnf), and serotonergic (5-HT) and dopaminergic (DA) neurotransmission (thp, th) were also measured. SI altered social behaviors in zebrafish such as aggression, social preference, and shoaling. Fish submitted to SI also presented changes in the transcript levels of genes related to neural activity, and 5-HT/DA signaling. Interestingly, most of the behavioral and molecular changes induced by SI were not found again 6 days after SR. Thus, we highlight that SR of zebrafish to their conspecifics played a positive role in social behaviors and in the expression of genes involved in different neuronal signaling pathways that were altered after 12 days of SI. This study brings unprecedented data on the effects of SR in the recovery from SI neurobehavioral alterations, and reinforces the role of zebrafish as a translational model for understanding the neurobiological mechanisms adjacent to SI and resocialization.

Behavioral profile of adult zebrafish acutely exposed to a selective dopamine uptake inhibitor, GBR 12909.

BACKGROUND: The dopamine transporter (DAT) is the main regulator of dopamine concentration in the extrasynaptic space. The pharmacological inhibition of the DAT results in a wide spectrum of behavioral manifestations, which have been identified so far in a limited number of species, mostly in rodents. AIM: Here, we used another well-recognized model organism, the zebrafish (Danio rerio), to explore the behavioral effects of GBR 12909, a highly-affine selective DAT blocker. METHODS: We evaluated zebrafish locomotion, novelty-related exploration, spatial cognition, and social phenotypes in the novel tank, habituation and shoaling tests, following acute 20-min water immersion in GBR 12909. RESULTS: Our findings show hypolocomotion, anxiety-like state, and impaired spatial cognition in fish acutely treated with GBR 12909. This behavioral profile generally parallels that of the DAT knockout rodents and zebrafish, and it overlaps with behavioral effects of other DAT-inhibiting drugs of abuse, such as cocaine and D-amphetamine. CONCLUSION: Collectively, our data support the utility of zebrafish in translational studies on DAT targeting neuropharmacology and strongly implicate DAT aberration as an important mechanisms involved in neurological and psychiatric diseases.

Mixed-species groups of herbivorous reef fishes show variable responses to ecosystem perturbations in the Lakshadweep Islands, India.

Herbivorous reef fishes provide a vital function in reef ecosystems by removing algae and making space available to coral recruits. The high abundance of herbivores in the reefs of the Lakshadweep islands has potentially aided in reef recovery and helped avoid a phase shift to an algal-dominated system, despite most areas having suffered massive coral losses. Mixed-species grouping in herbivores could potentially benefit both the participant species and the reef ecosystem by improving foraging efficiency. We examined the grouping propensity and species richness for three types of herbivore groups after a mass-bleaching event in 2010 and a mass recruitment event in 2015. The species richness and number of parrotfish groups, as well as the grouping propensity of common species, declined starkly across years, indicating that these groups may have formed in response to the mass-bleaching event, slowly diminishing as the reefs recovered. Conversely, large surgeonfish, which varied in richness and propensity across islands and aspect, are probably influenced by local processes. Small surgeonfish only increased in species richness and number in 2015, which may have been in response to the recruitment event. Thus, herbivorous fishes may respond differently to local ecosystem perturbations and play different roles in reef recovery. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.

Increased water temperature and turbidity act independently to alter social behavior in guppies (Poecilia reticulata).

Changes in environmental conditions can shift the costs and benefits of aggregation or interfere with the sensory perception of near neighbors. This affects group cohesion with potential impacts on the benefits of collective behavior such as reduced predation risk. Organisms are rarely exposed to one stressor in isolation, yet there are only a few studies exploring the interactions between multiple stressors and their effects on social behavior. Here, we tested the effects of increased water temperature and turbidity on refuge use and three measures of aggregation in guppies (Poecilia reticulata), increasing temperature and turbidity in isolation or in combination. When stressors were elevated in isolation, the distribution of fish within the arena as measured by the index of dispersion became more aggregated at higher temperatures but less aggregated when turbidity was increased. Another measure of cohesion at the global scale, the mean inter-individual distance, also indicated that fish were less aggregated in turbid water. This is likely due to turbidity acting as a visual constraint, as there was no evidence of a change in risk perception as refuge use was not affected by turbidity. Fish decreased refuge use and were closer to their nearest neighbor at higher temperatures. However, the nearest neighbor distance was not affected by turbidity, suggesting that local-scale interactions can be robust to the moderate increase in turbidity used here (5 NTU) compared with other studies that show a decline in shoal cohesion at higher turbidity (>100 NTU). We did not observe any significant interaction terms between the two stressors, indicating no synergistic or antagonistic effects. Our study suggests that the effects of environmental stressors on social behavior may be unpredictable and dependent on the metric used to measure cohesion, highlighting the need for mechanistic studies to link behavior to the physiology and sensory effects of environmental stressors.

Sex differences in the expression of aggressive behavior and influences on social choice in zebrafish (Danio rerio).

Aggregation behavior (grouping) provides many animals with the ecological benefits of protection from predators, increased access to food, and greater mating opportunities, despite possible costs. Many factors likely contribute to the social choices animals make, and we sought to determine if the individual expression of aggression would correlate with shoalmate choices. We quantified aggressive or submissive tendencies of individual male and female zebrafish and shoalmate preferences within dichotomous choice assays. We hypothesized that fish, regardless of their individual aggressive behaviors, would benefit most and therefore choose to spend time near larger shoals and shoals of the opposite sex. Both sexes spent significantly more time near shoals rather than be alone. Males spent significantly more time with the largest shoal, and females exhibited a similar trend. Both sexes spent more time with shoals of females, rather than males. Males were generally more consistent in their aggressive behaviors across multiple assays and females exhibited more individual-variability. More aggressive male zebrafish were more likely to choose shoals of males over females and were more likely to swim alone, but female zebrafish did not exhibit a correlation between aggressive behaviors and social choices. Our results demonstrate clear sex differences in the expression of individual behavior and influences on shoaling.

Brain metabolite profiles provide insight into mechanisms for behavior sexual dimorphisms in zebrafish (Danio rerio).

The zebrafish (Danio rerio) has historically been a useful model for research in genetics, ecology, biology, toxicology, and neurobehavior. Zebrafish have been demonstrated to have brain sexual dimorphism. However, the sexual dimorphism of zebrafish behavior demands our attention, particularly. To evaluate the behavior and brain sexual dimorphisms in zebrafish, this study assessed sex differences in adult D. rerio in four behavioral domains, including aggression, fear, anxiety, and shoaling, and further compared with metabolites in the brain tissue of females and males. Our findings showed that aggression, fear, anxiety and shoaling behaviors were significantly sexually dimorphic. Interestingly, we also show through a novel data analysis method, that the female zebrafish exhibited significantly increased shoaling behavior when shoaled with male zebrafish groups and, for the first time, we offer evidence that male shoals are beneficial in dramatically alleviating anxiety in zebrafish. In addition, there were significant changes in metabolites in zebrafish brain tissue between the sexes. Furthermore, zebrafish behavioral sexual dimorphism may be associated with brain sexual dimorphism, with significant differences in brain metabolites. Therefore, to prevent the influence or even bias of behavioral sex differences on results, it is suggested that behavioral studies or behavioral-based other relevant investigations consider sexual dimorphism of behavior and brain.

A warmer environment can reduce sociability in an ectotherm.

The costs and benefits of being social vary with environmental conditions, so individuals must weigh the balance between these trade-offs in response to changes in the environment. Temperature is a salient environmental factor that may play a key role in altering the costs and benefits of sociality through its effects on food availability, predator abundance, and other ecological parameters. In ectotherms, changes in temperature also have direct effects on physiological traits linked to social behaviour, such as metabolic rate and locomotor performance. In light of climate change, it is therefore important to understand the potential effects of temperature on sociality. Here, we took the advantage of a 'natural experiment' of threespine sticklebacks from contrasting thermal environments in Iceland: geothermally warmed water bodies (warm habitats) and adjacent ambient-temperature water bodies (cold habitats) that were either linked (sympatric) or physically distinct (allopatric). We first measured the sociability of wild-caught adult fish from warm and cold habitats after acclimation to a low and a high temperature. At both acclimation temperatures, fish from the allopatric warm habitat were less social than those from the allopatric cold habitat, whereas fish from sympatric warm and cold habitats showed no differences in sociability. To determine whether differences in sociability between thermal habitats in the allopatric population were heritable, we used a common garden breeding design where individuals from the warm and the cold habitat were reared at a low or high temperature for two generations. We found that sociability was indeed heritable but also influenced by rearing temperature, suggesting that thermal conditions during early life can play an important role in influencing social behaviour in adulthood. By providing the first evidence for a causal effect of rearing temperature on social behaviour, our study provides novel insights into how a warming world may influence sociality in animal populations.

Adapting classic paradigms to analyze alterations of shoal-wide behavior in early-life stages of zebrafish (Danio rerio) - A case study with fluoxetine.

Given the strong increase in prescription of neuroactive pharmaceuticals, neurotoxicity has received growing concern in science and the public. Regulatory requirements stimulated the development of new methods to evaluate the risk of neurotoxic substances for humans and the environment, and, with respect to potential damage to aquatic ecosystems, a variety of behavior-based assays have been proposed for neurotoxicity testing, most of which, however, are restricted to changes in the behavior of individual fish. Since many fish species form shoals under natural conditions, this may cause important aspects of behavior to be overlooked and there is a need for behavior assays integrating individual behavior with behavior of the entire swarm. In order to combine more environmentally realistic sub-chronic exposure scenarios with undistorted social behavior and animal welfare considerations, two behavioral assays are proposed that might be integrated into early-life stage toxicity studies according to OECD TG 210, which are commonly run for a multitude of regulations: To this end, protocols for a novel tank test and a predator response assay were adapted to also record the behavior of free-swimming zebrafish (Danio rerio) juveniles within shoals. Comparisons of the diving response (novel tank) or the shoal's coherence and position relative to the stimulus (predator) with control groups allow conclusions about the anxiety state of the fish, which might well have an impact on survival chances in the wild. As a model substance, the antidepressant fluoxetine ((RS)-N-Methyl-3-phenyl-3-(4-trifluoromethylphenoxy)propylamine) produced adverse effects down to concentrations three orders of magnitude below the EC10 from acute fish embryo toxicity tests according to OECD TG 236. With the integration of such behavior tests into OECD TG 210, important population-relevant information on potential neurotoxicity can be collected without increasing the number of experimental animals.

Zebrafish (Danio rerio) shoaling in light and dark conditions involves a complex interplay between vision and lateral line.

We know little about how - or even if in some species - fish shoal in darkness. We hypothesized that 'dark shoaling' occurs in zebrafish and therefore must depend upon lateral line sensory input. Shoaling in groups of five adult zebrafish was analyzed with motion tracking software. We measured average inter-individual distance, time near the arena wall (thigmotaxis zone) and total distance traveled under normal room light, and in near-complete darkness (infrared light at 850 nm). These observations were repeated in fish treated with cobalt chloride (CoCl2), which ablates lateral line function. In untreated controls, dark shoaling was reduced compared to in light, but nonetheless still present. Elimination of lateral line sensory input by CoCl2 treatment similarly reduced, but did not eliminate, shoaling under both light and dark. Our findings indicate that normal zebrafish shoaling in light or dark requires both visual and lateral line inputs, with neither alone sufficient for normal shoaling.

What drives mixed-species shoaling among wild zebrafish? The roles of predators, food access, abundance of conspecifics and familiarity.

Mixed-species groups occur across a wide range of faunal communities and provide several benefits to members. While zebrafish have often been observed to form mixed-species shoals with coexisting species, the factors determining their occurrence are not yet fully understood. Shoals comprising zebrafish (Danio rerio), flying barbs (Esomus danricus), and whitespots (Aplocheilus panchax) were collected from a stagnant canal at Haringhata (West Bengal, India), and using laboratory-based experiments, we deciphered likely drivers of mixed-species shoaling among zebrafish. Experiments assessing foraging efficiency revealed that the amount of food consumed by individual zebrafish in mixed shoals was comparable to the amount consumed by these individuals in conspecific shoals. Within mixed-species shoals, zebrafish individuals, despite being smaller than the other species, consumed a comparable amount of food as the other species. Shoal choice experiments revealed that under predator risk, zebrafish associate more with mixed shoals and showed comparable associations to shoals differing in the abundance of conspecifics. Furthermore, zebrafish preferred associating with familiar conspecifics over unfamiliar mixed and unfamiliar conspecific shoals. Therefore, equitable food consumption in mixed shoals, greater association with mixed shoals in the presence of predators, and familiarity were important in driving zebrafish towards mixed-species shoaling. This article has an associated First Person interview with the first author of the paper.

Acute Administration of Ethanol and of a D1-Receptor Antagonist Affects the Behavior and Neurochemistry of Adult Zebrafish.

Alcohol abuse represents major societal problems, an unmet medical need resulting from our incomplete understanding of the mechanisms underlying alcohol's actions in the brain. To uncover these mechanisms, animal models have been proposed. Here, we explore the effects of acute alcohol administration in zebrafish, a promising animal model in alcohol research. One mechanism via which alcohol may influence behavior is the dopaminergic neurotransmitter system. As a proof-of-concept analysis, we study how D1 dopamine-receptor antagonism may alter the effects of acute alcohol on the behavior of adult zebrafish and on whole brain levels of neurochemicals. We conduct these analyses using a quasi-inbred strain, AB, and a genetically heterogeneous population SFWT. Our results uncover significant alcohol x D1-R antagonist interaction and main effects of these factors in shoaling, but only additive effects of these factors in measures of exploratory behavior. We also find interacting and main effects of alcohol and the D1-R antagonist on dopamine and DOPAC levels, but only alcohol effects on serotonin. We also uncover several strain dependent effects. These results demonstrate that acute alcohol may act through dopaminergic mechanisms for some but not all behavioral phenotypes, a novel discovery, and also suggest that strain differences may, in the future, help us identify molecular mechanisms underlying acute alcohol effects.

Fentanyl Induces Novel Conditioned Place Preference in Adult Zebrafish, Disrupts Neurotransmitter Homeostasis, and Triggers Behavioral Changes.

Abuse of new psychoactive substances increases risk of addiction, which can lead to serious brain disorders. Fentanyl is a synthetic opioid commonly used in clinical practice, and behavioral changes resulting from fentanyl addiction have rarely been studied with zebrafish models. In this study, we evaluated the rewarding effects of intraperitoneal injections of fentanyl at concentrations of 10, 100, and 1000 mg/L on the group shoaling behavior in adult zebrafish. Additional behavioral tests on individual zebrafish, including novel tank, novel object exploration, mirror attack, social preference, and T-maze memory, were utilized to evaluate fentanyl-induced neuro-behavioral toxicity. The high doses of 1000 mg/L fentanyl produced significant reward effects in zebrafish and altered the neuro-behavioral profiles: reduced cohesion in shoaling behavior, decreased anxiety levels, reduced exploratory behavior, increased aggression behavior, affected social preference, and suppressed memory in an appetitive associative learning task. Behavioral changes in zebrafish were shown to be associated with altered neurotransmitters, such as elevated glutamine (Gln), gamma-aminobutyric acid (GABA), dopamine hydrochloride (DA), and 5-hydroxytryptamine (5-HT). This study identified potential fentanyl-induced neurotoxicity through multiple neurobehavioral assessments, which provided a method for assessing risk of addiction to new psychoactive substances.

Collective response of fish to combined manipulations of illumination and flow.

Collective behavior is ubiquitous among fish, yet, its hows and whys are yet to be completely elucidated. It is known that several environmental factors can dramatically influence collective behavior, by eliciting behavioral adaptations in the individuals and altering physical pathways of social interactions in the group. Yet, empirical research has mostly focused on the quantification of the role of one factor at a time, with a paucity of studies designed to explore the multi-sensory basis of collective behavior. We investigated collective behavior of zebrafish (Danio rerio) pairs swimming in a water channel under combined manipulations of illumination (bright and dark) and flow conditions (absence and presence). The ability of the pair to orient and school increased in the presence of the flow and when fish were allowed to visually interact under bright illumination. Shoaling, instead, was only modulated by the illumination, so that fish swam at higher relative distances in the dark, irrespective of the flow. We also found evidence in favor of a modulatory effect of flow and illumination on the formation of the pair. Specifically, in the bright illumination, fish swam more side-by-side against a flow than in placid water; likewise, in the presence of a flow, they spent more time side-by-side in the bright illumination than in the dark. These findings point at a rich interplay between flow and illumination, whose alterations have profound effects on collective behavior.

Skin bacterial microbiome diversity predicts lower activity levels in female, but not male, guppies, Poecilia reticulata.

While the link between the gut microbiome and host behaviour is well established, how the microbiomes of other organs correlate with behaviour remains unclear. Additionally, behaviour-microbiome correlations are likely sex-specific because of sex differences in behaviour and physiology, but this is rarely tested. Here, we tested whether the skin microbiome of the Trinidadian guppy, Poecilia reticulata, predicts fish activity level and shoaling tendency in a sex-specific manner. High-throughput sequencing revealed that the bacterial community richness on the skin (Faith's phylogenetic diversity) was correlated with both behaviours differently between males and females. Females with richer skin-associated bacterial communities spent less time actively swimming. Activity level was significantly correlated with community membership (unweighted UniFrac), with the relative abundances of 16 bacterial taxa significantly negatively correlated with activity level. We found no association between skin microbiome and behaviours among male fish. This sex-specific relationship between the skin microbiome and host behaviour may indicate sex-specific physiological interactions with the skin microbiome. More broadly, sex specificity in host-microbiome interactions could give insight into the forces shaping the microbiome and its role in the evolutionary ecology of the host.

Acetic acid-induced nociception modulates sociability in adult zebrafish: Influence on shoaling behavior in heterogeneous groups and social preference.

Due to the recognition of fishes as sentient beings, the zebrafish (Danio rerio) has become an emergent animal model system to investigate the biological processes of nocifensive responses. Here, we aimed to characterize the zebrafish social behavior in a nociception-based context. For this purpose, using a three-dimensional analysis of heterogeneous shoals, we investigated the main behavioral responses in two 6-min trials: before (baseline) and after a single intraperitoneal (i.p) injection of 10 µL phosphate-buffered saline (PBS) (control), acetic acid 5% (AA), morphine 2.5 mg/kg (MOR) or acetic acid 5% plus morphine 2.5 mg/kg (AA + MOR) in one subject from a four-fish shoal. The social preference of individuals for tanks with shoals of fish treated with PBS, 5 % AA, or to an empty aquarium was also tested. We verified that AA administration disrupted the shoal homogeneity by eliciting dispersion of the treated fish with simultaneous clustering of non-manipulated fish. In general, morphine coadministration protected against AA-induced behavioral changes. The social preference test revealed a clear preference to conspecifics (PBS and AA) over an empty tank. However, a prominent preference for PBS- over AA-treated shoal was verified. Overall, our novel findings show that nociception can modulate zebrafish sociability, possibly due to the visual recognition of nocifensive responses. Although future studies are needed to elucidate how nociception modulates zebrafish social behavior, our results contribute to improve the welfare assessment of zebrafish shoals under distinct experimental manipulations.

Weathering-Resistant Replicas Fabricated by a Three-Dimensional Printing Robotic Platform Induce Shoaling Behavior in Zebrafish.

In recent decades, zebrafish have become an increasingly popular laboratory organism in several fields of research due to their ease of reproduction and rapid maturation. In particular, shoaling behavior has attracted the attention of many researchers. This article presents a fully printed robotic model used to sense and stimulate shoaling behavior in zebrafish (Danio rerio). Specifically, we exposed laboratory-fabricated replicated materials to critical acid/base/salt environments and evaluated the mechanical, optical, and surface properties after a three-month immersion period. Focusing on weatherability, these test samples maintained high tensile strength (~45 MPa) and relatively similar transmission (>85%T in the visible region), as determined by UV−vis/FTIR spectroscopy. Three-dimensional (3D) printing technology allowed printing of models with different sizes and appearances. We describe the sense of zebrafish responses to replicas of different sizes and reveal that replicas approximating the true zebrafish size (3 cm) are more attractive than larger replicas (5 cm). This observation suggests that larger replicas appear as predators to the zebrafish and cause fleeing behavior. In this study, we determined the weatherability of a high-transparency resin and used it to fabricate a fully printed driving device to induce shoaling by zebrafish. Finally, we demonstrate a weathering-resistant (for three months) 3D-printed decoy model with potential utility for future studies of outdoor shoaling behavior, and the result has the potential to replace the traditional metal frame devices used in outdoor experiments.

Combined effect of diazepam and polystyrene microplastics on the social behavior of medaka (Oryzias latipes).

The combined effect of microplastics and pharmaceuticals on aquatic organisms is an issue of concern. In this laboratory study, we evaluated the combined effect of polystyrene microplastics (2-µm diameter) and diazepam on the social behavior of medaka (Oryzias latipes) by using the shoaling behavior test with five treatment groups: solvent control, polystyrene microplastics exposure (0.04 mg/L), low-concentration diazepam exposure (0.03 mg/L), high-concentration diazepam exposure (0.3 mg/L), and polystyrene microplastics and low-concentration diazepam co-exposure. After 7 days of exposure, the shoal-leaving behavior of the high-concentration diazepam exposure group (8.9 ± 8.3 counts/medaka) and the co-exposure group (6.8 ± 6.7 counts/medaka) was significantly greater than that in the solvent control group (1.8 ± 2.6 counts/medaka). Even after 5 days of recovery, medaka in the co-exposure group left the shoal more often (7.3 ± 5.0 counts/medaka) than those in the solvent control group (2.6 ± 2.6 counts/medaka), whereas the shoal-leaving behavior in other exposure groups, except for the high-concentration diazepam exposure group, was restored. Our findings show that the combined effects of diazepam and polystyrene microplastics suppressed medaka social behavior, suggesting that the presence of microplastics can enhance the adverse effects of pollutants on the social behavior of aquatic organisms.

Emergence and repeatability of leadership and coordinated motion in fish shoals.

Studies of self-organizing groups like schools of fish or flocks of birds have sought to uncover the behavioral rules individuals use (local-level interactions) to coordinate their motion (global-level patterns). However, empirical studies tend to focus on short-term or one-off observations where coordination has already been established or describe transitions between different coordinated states. As a result, we have a poor understanding of how behavioral rules develop and are maintained in groups. Here, we study the emergence and repeatability of coordinated motion in shoals of stickleback fish (Gasterosteus aculeatus). Shoals were introduced to a simple environment, where their spatio-temporal position was deduced via video analysis. Using directional correlation between fish velocities and wavelet analysis of fish positions, we demonstrate how shoals that are initially uncoordinated in their motion quickly transition to a coordinated state with defined individual leader-follower roles. The identities of leaders and followers were repeatable across two trials, and coordination was reached more quickly during the second trial and by groups of fish with higher activity levels (tested before trials). The rapid emergence of coordinated motion and repeatability of social roles in stickleback fish shoals may act to reduce uncertainty of social interactions in the wild, where individuals live in a system with high fission-fusion dynamics and non-random patterns of association.

Male zebrafish (Danio rerio) do not preferentially associate with familiar over unfamiliar conspecifics.

Members of several shoaling species have been shown to prefer to associate with familiar individuals, enhancing the benefits of aggregation. The authors used a series of social preference tasks in the laboratory to evaluate whether prior familiarity with potential partners influences preference of shoaling partner in male zebrafish (Danio rerio), a social species found in shallow, slow-moving waters. The authors found that though male zebrafish exhibited a strong preference for shoaling with a male conspecific as opposed to remaining alone, they exhibited no preference for familiar over unfamiliar conspecifics. This suggests that the benefits of familiarity for shoaling behaviour may not be as important for male zebrafish as has been shown in other social fish species.