Plasma sex steroid concentrations in male blue cod, Parapercis colias (Bloch & Schneider) (Pinguipedidae), sampled underwater during the spawning season

Abstract

Blood samples were collected underwater from male blue cod (Parapercis colias) captured by SCUBA divers during the spawning season. Acute reproductive condition (degree of spermiation) and size were determined, after which the fish were released. In all, 82 fish were sampled during 13 dives in daylight hours over a 10-week period. Fish that were not spermiated were most common before 1000 hours, whereas most of the spermiated fish were captured after 1500 hours. Spawning has yet to be observed, but available evidence suggests that it occurs in the late afternoon or early evening, although it is not known how frequently spawning acts occur. Plasma testosterone (T) concentrations were variable but did not show consistent association with date, time of sampling, moon phase or acute reproductive condition. Plasma T was higher in large males than in small males in all spermiation stages. There was no clear relationship between plasma T and T-glucuronide concentrations. Plasma 11-ketotestosterone (IIKT) concentrations were less variable than T concentrations but, like T, were higher in large fish than in small fish. Plasma 17a,20ßP-dihydroxy-4-pregnen-3-one (17,20ßP was not detectable at any time, but the presence of 17,20ßP-glucuronide (17,20ßPG) indicated that 17,20ßP was being produced and glucuronated before it accumulated to detectable concentrations in the plasma. In spermiated fish, 17,20ßPG was elevated.