Plasma levels of C18‐, C19‐ and C21‐steroids in captive and feral female sea bass

Abstract

Morphometric analysis of the gonads of sea bass Dicentrarchus labrax revealed that captive fish matured 1 month later than feral fish, but levels of gonadal steroids were identical in both groups at the same stage of sexual development. 17β‐oestradiol (E2) (up to 3 ng ml‐1) and testosterone (T) (up to 4 ng ml‐1) were highest during the gametogenetic period while 17,20β,21‐trihydroxy‐4‐pregnen‐3‐one (17,20β,21‐P) (free and sulphated) were maximal during the spawning period. Free 17,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β‐P) was very low and did not change (c. 0·5 ng ml−1) while 17,20β‐P‐sulphate increased during the spawning period in both groups (up to 2 ng ml−1). In contrast cortisol levels were higher in captive fish and increased during the spawning period (up to 100 ng ml−1). These results suggest that captivity delays vitellogenesis and spawning in sea bass without affecting the final levels of the gonadal steroids and further indicates a role for cortisol in the latter period. The increased levels during the spawning period suggests a pheromonal role for 17,20β‐P‐sulphate and 17,20β,21‐P‐conjugates and the involvement of 17,20β,21‐P in final ooccyte maturation.