Biochemical cost of a fight in fed and fasted Betta splendens.

Behavioral and biochemical effects of threat displays and fights were determined in both fed and fasted animals. A week-long fast resulted in subtle behavioral modifications and a significant reduction in muscle glycogen. Threat displays had no effect on carcass composition. In the course of fighting, fed animals degraded large amounts of lipids, glycogen and amino acids, while fasted animals degraded only glycogen. Two alternative hypotheses are proposed to explain the difference between the biochemical effects of a fight in fed and starved animals.