Reproductive condition and behavior in relation to plasma levels of gonadal steroids in the spiny damselfish Acanthochromis polyacanthus

Gonadal condition and plasma levels of gonadal steroids were measured in re lation to behavior in the biparental brood-protecting spiny damselfish Acan thochromis polyacanthus. Fish were captured by SCUBA divers from natural po pulations on Australia's Great Barrier Reef and immediately bled underwater , following diver or video observation of precapture behaviour. In winter ( July), most fish were nonterritorial, with a low proportion of mature males , or vitellogenic females present. In spring (November), most fish were ter ritorial with broods of young at varying stages of maturity, and all stages of gonadal development were represented. Territorial males were larger tha n nonterritorial fish, but territorial fish that had large (older) young (t he end of the brooding phase) had lower condition factors than fish at othe r stages. Males of all gonad stages had a high proportion of spermatozoa in the testis, but this was higher in November than in July. Ovaries of femal es commonly had several classes of developing follicles present, although f ish that were brooding large young had regressed ovaries with a high incide nce of atresia. Plasma levels of testosterone (T) and 11-ketotestosterone w ere elevated in males of advanced gonadal maturity, and also in relation to recent or imminent spawning behaviour, but there were no changes in plasma 17,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta P), which was near assay detection limits at all times. Females had elevated T and 17 beta-estradiol (E-2) in association with vitellogenesis and elevated T in relation to spa wning activity in some fish, but as in males, 17,20 beta P levels were low and unchanging. Territorial females without young had lower cortisol levels than nonterritorial fish, or females protecting young. The results confirm the importance of elevated androgens to spawning activity in territorial m ale fish, but not females where endocrine activity is more closely related to stage of ovarian development. Extended brooding appears to inhibit vitel logenesis, perhaps via a stress-related mechanism, (C) 1999 Academic Press.