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Selecting the most appropriate model organisms is crucial for studying ageing and ageing-related diseases. While vertebrate aging models offer valuable research feasibility due to their biological complexity and human relevance, their inherent lifespan limitations and high costs significantly restrict their experimental utility. The turquoise killifish (Nothobranchius furzeri, N. furzeri) is a relatively new animal model with the shortest lifespan among vertebrate models. We conducted a systematic review of the literature on N. furzeri following Prisma guidelines. We searched PubMed and Scopus databases, identifying 79 articles on ageing research in N. furzeri that met our inclusion criteria as of December 2024 and two independent reviewers screened and assessed all studies. We found that the ageing phenotypes of N. furzeri are highly consistent with those of other animal models. We screened and included literature on ageing mechanisms and focused our analysis on research results related to molecular biology and epigenetics. Compared to other fish models such as zebrafish, medaka, and fugu, N. furzeri offers several advantages for aging research, primarily due to its short lifespan, which provides unique insights from both physiological and genetic perspectives. However, several limitations must be considered. The current N. furzeri gene database remains incomplete, and the genetic background of this species is still not fully understood. Additionally, the mechanisms underlying the rapid ageing in N. furzeri have not yet been fully elucidated. Laboratory breeding of N. furzeri also lacks standardized processes and can be more challenging compared to other fish species. These factors may limit the widespread adoption of N. furzeri as an ageing model in the short term. Nevertheless, N. furzeri presents a novel, cost-effective, and rapid model for studying ageing-related diseases and mechanisms.

Individuals with divergent personality traits corresponding to stress coping styles have been suggested to differ in behavioural and neural plasticity. We used a model of social defeat stress to assess the coping ability of wild zebrafish selectively bred for boldness/shyness. Behavioural tests were applied to assess parameters such as boldness/exploration, aggressiveness, and displacement behaviour. Gene expression changes in the brain were assessed via RNA sequencing. The main results show a strong effect of shyness and boldness phenotype on behaviour and the brain transcriptome. Fish of the shy line displayed significant behavioural differences, while the number of differentially-expressed genes remained low. In contrast, fish of the bold line exhibited a small effect on behaviour and pronounced changes in brain gene expression. This study highlights the importance of boldness phenotype and its influence on the response to social challenges at the behavioural and transcriptomic levels.

Personality traits and acquired experience affect the capacity of an individual to cope with environmental and social changes. Behavioural adaptation and physiological alterations are important to prepare the body for these potential challenges. Whether inherited traits or acquired social rank (reflecting stress levels) are more important and how different personality-social rank combinations affect an individual's health is not well understood. One important aspect of health status is the function of biological barriers, as they represent the first line of defence of an organism. In the current study, we used a model of social defeat stress applied to a bold and a shy line of zebrafish. The Fulton's condition factor was determined, and gene expression analysis was performed on skin and intestines. The differences between lines explained a major part of the transcriptional changes observed as compared to differences in social rank. Additionally, shy fish that experienced repeated social defeat presented a poor body condition, accompanied by changes in gene expression suggesting inflammation in the gut. In the skin, shy fish showed a transcriptional enrichment of pathways related to cell division as well as increased expression of the stress response-associated gene crh2r. Together, these results complement our previous work and show that shy loser fish experience important changes not only in behaviour but also in their biological barriers, potentially putting their overall health at higher risk.

Coral reefs are among the most diverse and complex ecosystems. However, these habitats are currently facing severe pressures due to climate change, costal development and coral disease, influencing life on coral reefs. Considering that the degradation of the coral reefs can asymmetrically impact all organisms, we here asked if coral reef condition variability would be associated with change in stress and cleaning behaviour in Caribbean sharknose cleaning gobies Elacatinus evelynae. This study was conducted across five different reefs of the Island of Cura & ccedil;ao. We found significant differences in reef condition, in fish communities, in numbers of cleaning gobies and cleaning stations (i.e., goby territories) across all our sampled reefs. Specifically, the gobies from Carmabi (the most degraded reef) showed simultaneously lower cleaning activity and higher whole-body cortisol levels compared to gobies from other reefs. Collectively, our findings suggest that reef condition status may be implicated to stress and behavioural output variation of cleaning gobies.

The organization and function of the brain monoaminergic systems are largely conserved throughout the vertebrate subphylum. Mainly, these transmitter systems act as neuromodulators with important functions in arousal, behavioral responsiveness to environmental stimuli, and control of endocrine systems and, by that, subserve important roles in coordinating autonomic, neuroendocrine, and behavioral responses to challenges. Fish subjected to stress show a rapid activation of the monoaminergic systems. Activation of the dopaminergic and serotonergic system appears to have opposing effects; dopamine is associated with aggression and active behavioral responses, whereas serotonin acts inhibitory on aggression and behavioral responsiveness in general. Stress has also been reported to result in the activation of the histaminergic system and to have inhibitory effects on aggressive behavior, even though the effects of histamine are less clear. The brain norepinephric system is also activated by stress and seems to play a role in activating endocrine stress responses such as the elevation of plasma cortisol. In this review, the organization and function of brain monoaminergic systems in teleost fishes are discussed and compared to that in other vertebrates, mainly mammals. Also, the role of these systems in the stress response and the control of agonistic behavior is discussed.

Atlantic salmon (Salmo salar) display high levels of agonistic behavior in aquaculture farms, resulting in fin damage and chronic stress. Aggression affects fish growth and performance negatively and presents a serious welfare problem. Indeed, it would be beneficial to identify, separate or exclude overly aggressive individuals. Research on behavioral syndromes suggests that aggressive behavior may correlate with traits from other contexts, such as boldness and locomotory activity. We aimed to develop a high-throughput method to quantify and predict aggressive behavior of individual parr in hatchery-reared Baltic salmon (Salmo salar L.). We screened approximately 2000 parr in open field (OF) and mirror image stimulation (MIS) tests. We extracted seven variables from video tracking software for each minute of the tests; distance moved and duration moving (activity), the duration in and number of entries to the center of the arena (boldness), the distance moved in, and duration spent in the area adjacent to the mirror during the MIS test (aggressiveness) and head direction (lateralization). To investigate the relationship between activity, boldness, and aggression we first correlated the first six variables to one another. Second, we assigned individuals to high, medium, low or zero aggression groups based on the MIS test and quantified activity and boldness in each group. Third, we analyzed whether the fish viewed the mirror with the left or right eye. Our results show that medium and low aggressive fish were the most active, while highly aggressive fish showed average activity. Aggressive groups did not differ in boldness. Activity and boldness were positively correlated. Finally, we detected a preference for fish to view the mirror with the left eye. We conclude that although the OF may not accurately predict aggressive behavior, the MIS test can be used for large-scale aggression profiling of juvenile salmon

To understand the processes underpinning social decision-making, we need to determine how internal states respond to information gathered from the social environment. Brain monoamine neurotransmitters are key in the appraisal of the social environment and can reflect the internal state underlying behavioural responses to social stimuli. Here we determined the effects of conspecific partner cooperativeness during predator inspection on brain monoamine metabolic activity in Trinidadian guppies (Poecilia reticulata). We quantified the concentration of dopamine, serotonin and their metabolites across brain sections sampled immediately after ostensibly expe-riencing cooperation or defection from social partners whilst inspecting a predator model, using a familiar object as a control condition. Our results indicate dopaminergic and serotonergic activity differs with the coopera-tiveness experienced; these different neurotransmission profiles are likely to affect the expression and regulation of downstream behaviours that ultimately contribute to the patterning of cooperative interactions among in-dividuals in a population.

Over the last decade, the zebrafish has emerged as an important model organism for behavioural studies and neurological disorders, as well as for the study of metabolic diseases. This makes zebrafish an alternative model for studying the effects of energy disruption and nutritional quality on a wide range of behavioural aspects. Here, we used the zebrafish model to study how obesity induced by overfeeding regulates emotional and cognitive processes. Two groups of fish (n = 24 per group) were fed at 2% (CTRL) and 8% (overfeeding-induced obesity, OIO) for 8 weeks and tested for anxiety-like behaviour using the novel tank diving test (NTDT). Fish were first tested using a short-term memory test (STM) and then trained for four days for a long-term memory test (LTM). At the end of the experiment, fish were euthanised for biometric sampling, total lipid content, and triglyceride analysis. In addition, brains (eight per treatment) were dissected for HPLC determination of monoamines. Overfeeding induced faster growth and obesity, as indicated by increased total lipid content. OIO had no effect on anxiety-like behaviour. Animals were then tested for cognitive function (learning and memory) using the aversive learning test in Zantiks AD units. Results show that both OIO and CTRL animals were able to associate the aversive stimulus with the conditioned stimulus (conditioned learning), but OIO impaired STM regardless of fish sex, revealing the effects of obesity on cognitive processes in zebrafish. Obese fish did not show a deficiency in monoaminergic transmission, as revealed by quantification of total brain levels of dopamine and serotonin and their metabolites. This provides a reliable protocol for assessing the effect of metabolic disease on cognitive and behavioural function, supporting zebrafish as a model for behavioural and cognitive neuroscience.

Introduction; Despite its popularity in research, there is very little scientifically validated knowledge about the best practices on zebrafish (Danio rerio) husbandry, which has led to several facilities having their own husbandry protocols. This study was performed to expand knowledge on the effects of enrichment and fish density on the welfare of zebrafish, with hopes of providing a scientific basis for future recommendations and legislations.

Methods: Zebrafish were reared at three different stocking densities, (1, 3 or 6 fish/L), in tanks with or without environmental enrichment. Agonistic behavior was observed twice a week for 9 weeks directly in the housing tanks. Aspects of welfare is known to be reflected in neuroendocrine stress responses. Thus, cortisol secretion in response to lowering the water level was analyzed for each group. In addition, we assessed cortisol secretion in response to confinement and risk-taking behavior (boldness) using the novel tank diving test for individual fish. At termination of the experiment fish were subjected to stress by transfer to a novel environment and brain tissue was sampled for analysis of brain monoaminergic activity.

Results: Fish kept at the lowest density (1 fish/L) showed a significantly higher level of aggression than fish kept at 3 or 6 fish/L. Moreover, fish kept at this low density showed significantly higher cortisol secretion on a group level than fish kept at the higher stocking densities, when subjected to lowering of the water level. Keeping fish at 1 fish/L also had effects on brain monoamines, these fish showing higher brain dopamine concentrations but lower dopamine turnover than fish kept at higher densities. Neither stocking density or enrichment had any clear effects on the behavior of individual fish in the novel tank diving test. However, fish kept at high densities showed lower and more variable growth rates than fish kept at 1 fish/L.

Discussion: Taken together these results suggest that zebrafish should not be kept at a density of 1 fish/L. The optimal stocking density is likely to be in the range of 3-6 fish/L.

Zebrafish (Danio rerio) are becoming one of the most important model organisms in behavioural neuroscience. It has been shown repeatedly that different zebrafish strains show large behavioural differences. These divergent behavioural profiles may have a genetic basis, but environmental factors and previous experience are also known to greatly affect the behavioural phenotype of zebrafish. It could be expected that behavioural differences at the larval stage should be less affected by environmental factors and experience. In the present study, we screened larvae of zebrafish of the AB strain and offspring of wild-caught zebrafish for boldness, using an open field test. In order to follow the behavioural development, we studied larvae at the age of 5-, 7-, 12- and 30-days post fertilization (dpf). Behaviour, as well as behavioural development, clearly differed between the larvae of the different strains. Wild larvae showed larger total distance moved than AB larvae, both at light and dark conditions. These differences were already present at 12 dpf but became more pronounced with age. Wild larvae had a greater variance compared to AB larvae for most of the variables. We have previously shown that bold and shy adult zebrafish differ in the brain expression of dopamine and opioid receptors. The results of the current study show that wild larvae display significantly higher brain expression of drd2b than AB larvae at 30 dpf, a difference that could be related to differences in activity. We did not detect any differences in the expression of opioid receptors.