Effect of exogenous hormones on reproductive behaviour in territorial males of a natural population of demoiselles, Chromis dispilus (Pisces : Pomacentridae)

Abstract

Territorial male demoiselles (Chromis dispilus) engaged in egg brooding and defence were hand-netted from nest sites by divers and injected in situ with either des-Gly¹⁰ (D-Ala⁶) luteinizing-hormone-releasing hormone ethylamide (LHRHA), human chorionic gonadotrophin (hCG), 17α,20β- dihydroxy-4-pregnen-3-one (17,20βP), testosterone (T), or 11-ketotestosterone (11KT) in order to examine the effect of elevated 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 17,20βP, T, and 11KT by radioimmunoassay. The effect of egg presence on behaviour was assessed by removing the eggs from the nests of some fish. Underwater injections with hCG, LHRHA or gonadal steroids all resulted in increases in plasma 17,20βP, T and 11KT concentrations but did not stimulate the transition from brooding to display behaviour. Egg removal 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 nest. The results indicate that bioactive gonadotrophin-releasing hormone, gonadotrophin or gonadal steroids alone do not stimulate the transition from brooding to display and spawning behaviour in male demoiselles. Egg presence has a marked effect on the strength of association with the nest, but loss of eggs did not trigger the onset of display behaviour. It seems likely that a combination of events, including elevation of plasma concentrations of gonadal steroids and egg loss (hatching), stimulates the transition from brooding to display behaviour.