EFFECT OF EXOGENOUS HORMONES ON REPRODUCTIVE-BEHAVIOR IN TERRITORIAL MALES OF A NATURAL-POPULATION OF DEMOISELLES, CHROMIS-DISPILUS (PISCES, POMACENTRIDAE)

Territorial male demoiselles (Chromis dispilus) engaged in egg broodin g and defence were hand-netted from nest sites by divers and injected in situ with either des-Gly(10) (D-Ala(6)) luteinizing-hormone-releasi ng hormone ethylamide (LHRHA), human chorionic gonadotrophin (hCG), 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta P), testosterone (T), or 11-ketotestosterone (11KT) in order to examine the effect of e levated plasma steroid concentrations on the transition from brooding to spawning display behaviour (when plasma concentrations of steroids are typically elevated). Blood samples were analysed for 17,20 beta P, T, and 11KT by radioimmunoassay. The effect of egg presence on behavi our was assessed by removing the eggs from the nests of some fish. Und erwater injections with hCG, LHRHA or gonadal steroids all resulted in increases in plasma 17,20 beta P, T and 11KT concentrations but did n ot stimulate the transition from brooding to display behaviour. Egg re moval resulted in vacation of the territory by most fish within 24 h. There was no evidence of transition from brooding to display behaviour during the period after egg removal over which fish remained at the n est. The results indicate that bioactive gonadotrophin-releasing hormo ne, gonadotrophin or gonadal steroids alone do not stimulate the trans ition from brooding to display and spawning behaviour in male demoisel les. Egg presence has a marked effect on the strength of association w ith the nest, but loss of eggs did not trigger the onset of display be haviour. It seems likely that a combination of events, including eleva tion of plasma concentrations of gonadal steroids and egg loss (hatchi ng), stimulates the transition from brooding to display behaviour.