Abstract Understanding consistent inter-individual variability in animal behaviour, known as personality traits, is essential for exploring the mechanisms and evolutionary consequences of behavioural diversity. Aggressive behaviour influences survival, resource acquisition, and reproduction, so clarifying individual differences can enhance our understanding of ecological dynamics and improve experimental design accuracy in behavioural studies. In this study, ornamental male Betta splendens, a model organism for aggression research, were analysed for intra- and inter-individual variability in aggressive responses to their mirror image—a standard method for assessing aggression in fish—once per week, and their consistency was evaluated over three consecutive weeks There were significant differences in aggressive behaviour across individuals, with coefficients of variation ranging from 29 to 60%. While most fish exhibited the full suite of aggressive displays, some showed no aggressive behaviour, while others only displayed threat behaviours but did not advance to the attacks. The consistency of individual threat and attack behaviours varied, but repeatability was high overall (intra-class correlation coefficients ≥ 0.5), indicating that individual fish have different levels of aggression. There was habituation to the mirror assay, with aggression decreasing significantly by the second week, though the degree of habituation, a form of learning, varied among individuals in some behaviours. Air-breathing frequency correlated positively with aggression behaviours and can be considered an indicator to infer aggression level in this species. These results indicate that inter-individual variation in aggressive behaviour and habituation to repeated testing using the mirror assay should be considered in aggression studies using B. splendens and potentially in other species.

Recent years have witnessed the emergence of extensive new data suggesting a different view of inheritance from the view that has dominated biology for over a century. It suggests that what is transmitted across generations are the developmental means to construct phenotypes predicted to match anticipated environmental conditions. Those ‘developmental means’ include genes, but also other resources that parents bequeath to descendants, as well as activities parents engage in to construct the environmental context in which their offspring develop. If there are similarities between the traits of parents and offspring it is because, within lineages, phenotypes are reliably re-constructed across generations. Extra-genetic inheritance processes do an important job in evolution, but that job is, in the main, distinct from that of genetic inheritance. They are best regarded – not as noise, fine-tuning or baroque “add ons” (Wray et al. 2014) – but as essential tools for short-term, rapid-response adaptation. The true function of heredity is to make an informed forecast.

The earliest response to natural and anthropogenic changes in the environment is typically behavioural. Due to the relevance of animal behaviour in predicting and mitigating the impacts of environmental changes on populations and ecosystems the interdisciplinary field of Conservation Behaviour has recently emerged. While it was formally acknowledged as a discipline about 30 years ago, it was only in 2011 that a theoretical framework was proposed by Berger-Tal and colleagues. Currently, numerous examples illustrate the use of animal behaviour in conservation and management efforts. However, most of these examples involve terrestrial animals. This is partly because both the behaviour and habitats of terrestrial animals are more accessible than those in the marine environment. Here, I provide an overview on how animal behaviour can contribute to marine conservation, namely in assessing anthropogenic impacts on animal behaviour, using behaviour as indicators and in guiding conservation and management interventions, using examples from the marine environment. Finally, I discuss future directions and how major technological advances in equipment and in artificial intelligence can be critical for developing effective conservation strategies and policies in a rapidly changing world.