SEXUAL STEROIDS DURING PUBERTY IN MALE AFRICAN CATFISH (CLARIAS-GARIEPINUS) - SERUM LEVELS AND GONADOTROPIN-STIMULATED TESTICULAR SECRETIONIN-VITRO

Blood serum and testicular tissue samples were collected from 3 to 13- month-old African catfish (groups A-G) in order to study their puberta l development. The sampling covered the period from before the beginni ng of spermatogenesis until full maturity. Testes of fish in group A c ontained spermatogonia alone. In testes of group B, spermatogonia, spe rmatocytes and spermatids were present. Spermatozoa were first observe d in group C and became predominant as the fish attained full maturity (group G). Several sex steroids were determined in the blood samples. Testosterone was the quantitatively dominating androgen in the blood serum (3-5 ng.ml(-1)) in groups B and C (fish in group A were too smal l to collect blood samples). In group D, the concentrations of 11-keto testosterone and 11 beta-hydroxyandrostenedione increased to levels si milar to those of testosterone. Androstenedione that was undetectable before (below 0.4 ng.ml serum(-1)), also increased to 3-5 ng.ml(-1) in group D. The levels of androgens kept increasing until the fish attai ned full maturity (group G): In order to monitor the responsiveness to gonadotropic hormone and the steroid secretion capacity, the in vitro secretion of two steroids (11 beta-hydroxyandrostenedione and 17 alph a,20 beta-dihydroxy-4-pregnen-3-one) by testicular tissue was quantifi ed at the different stages of development. Testicular maturation was a ccompanied by changes of both the steroid secretion capacities and of the sensitivity to gonadotropic hormone. The most important changes oc curred just after the initiation of spermatogenesis, as spermatocyte/s permatid formation was associated with a drop of the secretory capacit y (amount of steroid secreted per milligram of tissue incubated) and w ith a reduced sensitivity to gonadotropic hormone. At later stages, wh en the testicular weight substantially increased concurrently with the formation of numerous spermatozoa, both the secretory capacity and th e responsiveness to gonadotropic hormone increased again to reach the levels typical of adult fish. The blood levels of androgens appeared t o be positively related to the increasing testicular weight in the lat er phases of development.