Variation in nest building, aggression, learning, and steroid hormone levels in Betta splendens.

Individuals within a population present behavioral responses that vary according to intrinsic and extrinsic factors such as ontogenetic phase, nutritional status, reproductive stage, and previous experiences. These differences can be explained by endogenous changes, such as hormone release, that can modulate reproductive behaviors, stress response, and cognitive processes. In order to investigate the relationship between behavior and hormonal levels in the fighting fish Betta splendens, the present study characterized nest building, aggressive behavior, learning of a task, and levels of cortisol and 11-ketotestosterone (11-KT) in 86 male Fighting fish.