Plasma levels of C-18-, C-19- and C-21-steroids in captive and feral female sea bass

Morphometric analysis of the gonads of sea bass Dicentrarchus labrax reveal ed that captive fish matured I month later than feral fish, but levels of g onadal steroids were identical in both groups at the same stage of sexual d evelopment. 17 beta-oestradiol (E-2) (up to 3 ng ml(-1)) and testosterone ( T) (up to 4 ng ml(-1)) were highest during the gametogenetic period while 1 7,20 beta,21-trihydroxy-4-pregnen-3-one (17,20 beta,21-P) (free and sulphat ed) were maximal during the spawning period. Free 17,20 beta-dihydroxy-4-pr egnen-3-one (17,20 beta-P) was very low and did not change (c. 0.5 ng ml(-1 )) while 17,20 beta-P-sulphate increased during the spawning period in both groups (up to 2 ng ml(-1)). In contrast cortisol levels were higher in cap tive fish and increased during the spawning period (up to 100 ng ml(-1)). T hese results suggest that captivity delays vitellogenesis and spawning in s ea bass without affecting the final levels of the gonadal steroids and furt her indicates a role for cortisol in the latter period. The increased level s during the spawning period suggests a pheromonal role for 17,20 beta-P-su lphate and 17,20 beta,21-P-conjugates and the involvement of 17,20 beta,21- P in final ooccyte maturation. (C) 1999 The Fisheries Society of the Britis h Isles.