A quantitative study of steroid bioconversions in the testis of the African catfish, Clarias gariepinus (Burchell), under natural spawning and natural and cultivated non-spawning conditions

Abstract

Quantitative aspects of bioconversions in the testes of the African catfish (Clarias gariepinus) were studied in vitro by incubation of tissue with [3H]pregnenolone or [3H]androstenedione. During the breeding period, spawning and non-spawning animals were collected from their natural habitat, the Hula nature reserve, in northern Israel. In the same period, non-spawning animals were collected from a fish pond in the same region. It was shown that spawning was accompanied by significant changes in steroid bioconversions, i.e. a reduction in androgen synthesis, especially of 11 beta-hydroxyandrostenedione and 11 beta-hydroxytestosterone and an increase in the production of C21-steroids, especially progesterone, 17 alpha-hydroxyprogesterone and a pregnenolone ester. These changes resulted from a decreased contribution of the cytochrome P-450 enzymes 17 alpha-hydroxylase, C17-20-lyase and 11 beta-hydroxylase. A rise in plasma gonadotrophin concentration was observed only in spawning catfish. In the absence of such an increase in plasma gonadotrophin, steroid synthesis in the testes of non-spawning feral and pond catfish was primarily directed towards the production of 11-oxygenated androgens and 5 beta-pregnane-3 alpha,17 alpha,20 alpha-triol. It is suggested that spawning is induced by gonadotrophin and the ensuing change in steroidogenesis. It is possible that husbandry conditions inhibit the necessary increase in gonadotrophin release.

The biosynthesis of steroid glucuronides in the testis of the zebrafish, Brachydanio rerio, and their pheromonal function as ovulation inducers

“…Concerning African catfish, it must be mentioned that the seminal vesicle is the main source of steroid glucuronides (Schoonen and Lambert, 1986b, Schoonen et al, 198%). The formation of 17a,20@dihydroxy-4-pregnen-3-one by the testes has previously been described in some other teleosts, i.e., the rainbow trout, S. gairdneri (Arai and Tamaoki, 1967;Kime 1979;Depeche and Sire, I982), and the African catfish, C.. gaviepinus (Schoonen and Lambert 1986a;Schoonen et al, 1987b). According ts Ueda et al (1984) it is the sperm that is involved in the final synthesis of 17aJO@di-hydroxy-4-pregnen-3-one.…”

“…Testosterone glucuronide is found to be produced by the testes of rainbow trout Salmo gairdmeri (Hews and Kime, 1978) and goldfish, G. auratus (Kime, 1980). The &reduced steroid glucuronides, however, have so far not been described as being synthesized by teleosr testes, whereas Sp-reduced steroid glucuronides have been found among the products of steroidogenesis in the testes of the black goby, G. jozo (Colombo et al,, 1977) and African catfish, Cla& gariepinus (Schoonen et al, 1987b). Concerning African catfish, it must be mentioned that the seminal vesicle is the main source of steroid glucuronides (Schoonen and Lambert, 1986b, Schoonen et al, 198%).…”

“…1701,,2Ou-Dihydroxy-4-pregnen-3-one was identified indirectly by eliminating other possibilities based on derivatization and Rf values (Schoonen et al, 1987b). The synthesis of 11-ketotestosterone, androsterone, and epiandrosterone was confirmed after incubations with [3H]androstenedione .…”

Steroidogenesis in the testes and seminal vesicles of spawning and non-spawning African catfish, Clarias gariepinus

“…The main steroids, identified by Schoonen and Lambert (1986a) and Schoonen et al (1987b) after in vitro incubation with [ 3H] -pregnenolone of minced testis tissue of spawning feral catfish and non-spawning pond catfish, are given in Fig. 1.…”

“…Since ll-ketotestosterone and testosterone were hardly produced, and llj?-hydroxytestosterone only to a relatively low extent during testicular recrudescence, the period of strong spermatogenic activity and the prespawning period (Resink et al, 1987a;Schoonen et al, 1987b), it seems that none of these androgens, but rather the much more abundant llj. ?-hydroxyandrostenedione, may stimulate the germinal epithelium and the development of the secondary sex characters of male African catfish during the prespawning season.…”