Changes in plasma levels of gonadal steroids and gonad morphology during the spawning cycle of male and female demoiselles Chromis dispilus (Pisces: Pomacentridae).

This study examined the relationship between gonad morphology and endocrine function of male and female demoiselles Chromis dispilus. Gonad samples were collected over two successive seasons and staged macroscopically and histologically. Blood samples were assayed for the gonadal steroids 17 beta-estradiol (E2), testosterone (T), 11-ketotestosterone (11KT), and 17 alpha,20 beta-dihydroxy-4-pregen-3-one (17,20 beta P) by radioimmunoassay. Histological examination indicated that demoiselles are multiple spawners with group synchronous gamete development, and gonad changes are synchronised within local populations. Gonad morphology does not differ between nonterritorial and territorial males. Plasma levels of E2 and T increased with vitellogenesis in female demoiselles. Plasma levels of 17,20 beta P did not change in association with final oocyte maturation, but 17,20 beta P was not excluded as the possible maturation inducing steroid. However, 17,20 beta P was elevated in females in association with spawning activity. Plasma levels of T and 11KT were not consistently associated with spermiation in male demoiselles but were elevated in association with spawning behaviour. Androgen levels were significantly higher during spawning in territorial males than in nonterritorial males. There was no association between 17,20 beta P and spermiation. Plasma levels of 17,20 beta P were elevated during the display and spawning period in territorial males only. The results of this study provide further evidence for the association of plasma levels of gonadal steroids and behavioural status in demoiselles.