Quantitative studies of steroid bioconversions in the seminal vesicles of spawning male African catfish, Clarias gariepinus (Burchell), under natural conditions, and of non-spawning catfish under natural and fish farm conditions

Abstract

1. 1. Steroid bioconversions in the seminal vesicles of Clarias gariepinus were studied quantitatively in vitro by tissue incubations with [ 3H]pregnenolone, [ 3H]androstenedione and [ 14C]11β-hydroxyandrostenedione, respectively. 2. 2. Spawning and non-spawning catfish, collected in the Hula nature reserve in northern Israel during the spawning period, and non-spawning animals, collected from a fish pond in the same region during the same period, were studied. 3. 3. Spawning animals showed a significantly higher production of 17α-hydroxyprogesterone, 5β-pregnan-17α-ol-3,20-dione and 5β-reduced androgens than non-spawning feral and pond catfish, as a result of a significantly increased contribution of the enzymes 5β-reductase and 3α-hydroxysteroid dehydrogenase (HSD). 4. 4. In spawning catfish the concentrations of gonadotropin in blood plasma were also significantly higher than in the plasma of non-spawning feral and pond catfish. This increase in gonadotropin level might have induced the rise in enzyme activity of 5β-reductase and 3α-HSD. 5. 5. It is concluded that the absence of a shift in steroidogenesis towards the production of 5β-reduced steroids may be among the factors preventing spontaneous spawning in male African catfish under husbandry conditions.