Changes in plasma levels of gonadal steroids during spawning behaviour in territorial male demoiselles Chromis dispilus (Pisces: Pomacentridae) sampled underwater.

Males of the demoiselle Chromis dispilus (a species endemic to New Zealand) were hand-netted from nest territories by scuba divers and blood sampled in situ. Reproductive condition and behaviour prior to capture were compared with plasma levels of testosterone (T) and 17 alpha,20 beta dihydroxy-4-pregnen-3-one (17,20 beta P). Spawning cycles of about 7 days, consisting of 1-2 days of spawning activity followed by 4-5 days of brooding behaviour, were observed. Plasma levels of T and 17,20 beta P were elevated (4-6 and 1-1.5 ng.ml-1, respectively) in fish that were engaged in courtship display, spawning, or guarding freshly spawned eggs. Levels of both hormones fell to less than 1 (T) and less than 0.4 ng.ml-1 (17,20 beta P) at the end of spawning episodes and remained low through the subsequent brooding period. T levels increased slightly toward the end of the brooding phase. Samples taken at 2- to 3-hr intervals during daylight hours showed similar correlation of steroid levels and activity; however, there was a marked fall in 17,20 beta P in spawning fish with the onset of shelter seeking at dusk. Values returned to high levels with the resumption of spawning the next day. Plasma steroid levels were not consistently correlated with reproductive condition (degree of spermiation). It is concluded that there is a strong correlation between plasma T and 17,20 beta P levels and the male spawning cycle, but not brooding or territorial behaviour per se.