About this Research Topic
Fish are the earliest appearing group of vertebrates, distributed in a wide radiation of species that represent different environments and adaptations. Most likely due to its early appearance in vertebrate evolution, fish were traditionally considered simple organisms from the point of view of nervous system complexity and behavior. This view is rapidly changing, as ethologists, behavioral psychologists, neuroscientists, and physiologists repeatedly demonstrate complex social behavior and flexible, intricate behavioral patterns that are related to emotionality in humans. Examples of the multiplex sociality of fish species include not only shoaling and aggressive interactions, but also the ability to negotiate social transactions, cooperation, complex mating strategies, and intricate male-female interactions. Not only are fish capable of complex social interactions, but these social interactions also have an important role in emotion-like behavior – for example, by being either a source or a buffer of stress, or by representing incentives in motivated behavior.
In addition to its importance in evolutionary biology and ethology, the study of social and emotion-like behavior in fish has gained traction due to the emergence and spread of fish as model organisms in neuroscience. While zebrafish are a major player in the field – being considered the third most important model organism in neuropharmacology and drug discovery – many have argued for an expansion of the breadth of model and reference species. For example, studying social and/or emotion-like behavior in other teleosts increases the chance of finding “core” mechanisms that are evolutionarily conserved and shared between species, including more evolutionary recent vertebrates. Moreover, studying other fish species also highlights the variation that can be found in this group, as well as across vertebrate groups.
Currently, a great variety of fish species are chosen to study social behavior to the point that they can now be understood as model organisms in the field. Cichlids (e.g., Nile tilapia, Burton’s mouthbreeder) are widely used in the study of social stress and social plasticity in dominant-subordinate hierarchies. Poeciliids (e.g., guppies, swordtails) are used to study sexual selection and male-female interactions. Cleanerfish (e.g., cleaner wrasse) are used to study cooperation and social cognition. And even zebrafish are increasingly being chosen to study more complex social behavior, as well as its implications to emotionality.
These studies are not solely relevant for clade-specific variation but are crucial to understanding how conserved brain mechanisms across vertebrates are. Indeed, fish were essential for the major discovery of conserved structures that form the “social decision-making network (SDMN)”, which is still being expanded. The SDMN is a network of structures, that include telencephalic, hypothalamic, and midbrain regions, showing high expression of genes involved in sociality (e.g., sex hormone receptors, nonapeptides, etc.) that have a key role in the modulation of social behaviour. Interestingly, most structures of the SDMN also appear to be part of a “reward network” and a “brain aversive/fear system”.
This Research Topic aims to present new evidence and, above all, a clearer picture of the crucial role that social and emotional function plays in fish behavior, and neurochemical and neurophysiological organization. Manuscripts that focus on social and emotion-like behavior in fish, combined with the neuronal, behavioral, and psycho-social aspects are welcome. The core aim is to showcase all the complexity of fish behavior that has recently emerged in the field and lay out future avenues of research.
Keywords: emotion, sociability, social decision-making, neuroscience, fish
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