Arginine vasotocin neuronal phenotypes and their relationship to aggressive behavior in the territorial monogamous multiband butterflyfish, Chaetodon multicinctus.

Intra and interspecific comparisons of arginine vasotocin (AVT) and its mammalian homolog arginine vasopressin (AVP) demonstrate several relationships between these neuropeptides and aggression/dominance behaviors. Prior studies in coral reef butterflyfishes and other fishes indicate that features of AVT neurons in the gigantocellular preoptic area (gPOA) and axon varicosities within the ventral nucleus of the ventral telencephalon should have a positive relationship with aggressive behavior, whereas AVT-ir neuronal features in the parvocellular preoptic area (pPOA) should have a negative relationship. We measured the offensive aggression of wild caught territorial monogamous multiband butterflyfish, Chaetodon multicinctus, in a simple lab paradigm that controlled for social context and variations in social stimuli. Offensive aggression did not follow a clear stereotyped pattern, but rather a complex sequence that includes five action patterns and two approach behaviors. We then used immunohistochemistry to test for associations between AVT immunoreactive features and projections with overall offensive aggression. Our results indicate that gPOA cell number was positively related to aggression while both the size and number of pPOA cells were negatively related to aggression. No association between aggression and the number of axon varicosities in the telencephalic region proposed to be associated with aggression was found. This study provides further support for the relationship between AVT neuronal features and aggression in fishes, and provides preliminary evidence that this relationship may relate to the motivation to produce aggressive behaviors in the immediate future.