THE NATURAL GONADAL CYCLE IN THE AFRICAN CATFISH CLARIAS GARIEPINUS; A BASIS FOR APPLIED STUDIES ON ITS REPRODUCTION IN FISH FARMS

ABSTRACT

Based on morphological criteria and the distribution and activity of the enzyme 3β-hydroxy steroid dehydrogenase (3β-HSD), the annual reproductive cycles of the gonads of the African catfish Clarias gariepinus, collected in the Hula Reserve in northern Israel, have been divided into different stages. The testis cycle comprised four stages: preparatory, prespawning, spawning and postspawning. The ovarian cycle comprised six stages: previtellogenesis, endogenous and exogenous vitellogenesis, postvitellogenesis, spawning and atresia. The occurrence of these stages during the annual cycle enables the division of this cycle into three periods; the resting period (September—February), the period of full gametogenesis (March—April) and the breeding period (May—August). Fish from the Buteiha area of Lake Kinneret, collected from November until January, preceded those from the Hula region in gametogenesis and 3β-HSD activity, probably due to the higher water temperature in the lake. Production of gametes and steroids are interrupted during the breeding period even under high temperature and normal feeding conditions. The enzyme 3β-HSD is localized in testicular Leydig cells, interstitial cells, special theca cells and granulosa cells of vitellogenic follicles of the ovaries. The changes in enzyme activity coincide with the gametogenetic cycle. It is concluded that Clarias gariepinus has a discontinuous reproductive cycle which can be influenced by temperature, providing possibilities for continuous production of healthy larvae under adequate fish culture conditions.