The effects of exogenous 11-ketotestosterone, testosterone, and cyproterone acetate on prespawning and parental care behaviors of male bluegill.

This study investigated the effect of exogenous 11-ketotestosterone (11KT) and testosterone (T), two important androgens involved in fish reproduction, as well as cyproterone acetate (CYA), an antiandrogen, on behaviors of male bluegill (Lepomis macrochirus) during prespawning and parental care periods. Parental male bluegill build nests in colonies, spawn with females, and then remain alone on these nests to provide care for their developing offspring. Implantation of pellets containing either 11KT or T did not induce parental males to build nests in early spring, before the onset of natural spawning, or during late spring and early summer, when the reproductive season was in progress. Treatment with pellets containing CYA inhibited reproduction in male bluegill and these fish did not spawn for the remainder of the reproductive season. The release of appropriate steroids from pellets to the serum was confirmed in all cases by a radioimmunoassay. Interestingly, nesting males that spawned successfully and were implanted with 11KT at the onset of the parental care phase displayed increased rim-circling, a behavior characteristic of the late prespawning period. Treatment with T or CYA, however, did not induce such behaviors in nesting bluegill. Finally, none of these treatments significantly affected antipredator aggressive behavior displayed by nesting males. Our results suggest that parental care behaviors in male bluegill are most likely expressed through nonandrogenic mechanisms.