Pituitary gonadotropin contents and ultrastructure of the gonadotrops in the African catfish Clarias gariepinus during the annual cycle in a natural habitat

Abstract

Over a period of 1 year, male and female specimens of a natural population of African catfish, Clarias gariepinus, were collected monthly at locations in northern Israel. Both the ultrastructural appearance of the gonadotrops and the pituitary gonadotropin content in males and females showed cyclical changes, which paralleled alterations in the reproductive cycle. In summer, during the breeding period, the gonadotrops were large and fully granulated, and pituitary gonadotropin reached maximum levels. After spawning, the resting period begins, with an increasing number of fusion products of secretory granules and globules in the gonadotrops, probably indicating a breakdown of hormone storage. This was followed by the appearance of residual bodies, cell shrinkage, and a considerable drop in pituitary gonadotropin content. In late winter and early spring, during gonadal recrudescence, the gonadotrops redeveloped, i.e., they increased in size and granulation, and at the same time the pituitary gonadotropin content augmented. This reproductive cycle will permit induced spawning and artificial propagation of African catfish from March till September. However, keeping the catfish at favourable feeding and temperature conditions may also permit the gonadotrops to produce gonadotropin continuously, thus providing the possibility of complete gametogenesis and of obtaining viable eggs and healthy larvae throughout the year.