Neuronal and neuroendocrine mechanisms of social rank and stress coping in teleost fish

Abstract

Fights for social dominance are stressful and results in an activation of the brain serotonergic system. Subordinate animals in an established dominance hierarchy are characterized by a chronic elevation of brain serotonergic activity, an effect that seems to mediate the behavioural inhibition observed in these animals. By contrast, social dominance has been associated with elevated dopaminergic activity, and dopamine (DA) has behavioural effects to some extent opposing those of serotonin (5HT). In addition to effects of the social environment, brain monoaminergic functions are controlled by genetic factors. For instance, zebrafish (Danio rerio) classified as bold, showing a propensity for being social dominant, display higher expression of DA2b receptor mRNA than shy conspecifics. In rainbow trout (Oncorhynchus mykiss) and Baltic salmon (Salmo salar) bold and shy individuals differ in the expression of 5HT1A receptor mRNA. In salmonids, bold and shy fish also show divergent effects of stress on brain 5HT neurotransmission. Personality traits are to a large extent genetically controlled. However, teleost fish are extremely plastic and it is not clear to what extent “personality related” differences in monoaminergic, and peptidergic, systems is related to heritable factors or early social interaction.