Immunocytochemical and histological studies on the hypophyseal-gonadal system in the freshwater nile tilapia, oreochromis niloticus (L.), during sexual maturation and spawning in different habitats

The activities of the hypophyseal-gonadal system of O. niloticus in different habitats were investigated using immunocytochemical and histological techniques. The observed physico-chemical results indicated that Lake Nasser water characteristics are within the allowed and desired safety baseline levels. In contrast, Lake Manzalah exhibited high levels of Ca(2+), Mg(2+), SO(4)(2-) and heavy metals (Zn, Pb, and Cd). These water conditions affected the activity of the hypophyseal-gonadal axis of tilapia. The secretory and the synthetic activities of GTH and SL cells in the pituitary gland, in general, underwent obvious normal changes during gonad maturation and spawning of O. niloticus in Lake Nasser. In Lake Manzalah, the secretory activity of GTH and SL cells declined. This may be due to the effect of the high levels of heavy metals which interfere with the release of hormones and disturb the feedback mechanisms. In addition, the activity of both PRL and GH cells in Lake Nasser was higher than that of Lake Manzalah, but the synthetic activity of the ACTH and MSH cells was higher in Lake Manzalah. This may be related to the increased stress on fishes and the dark polluted water in Lake Manzalah. Both the environmental and the endocrine impacts in Lake Manzalah caused a decline in the gonadal activity as reflected by the decrease of sperm amount in the ripe testis, the appearance of oocytes in the testis and the degeneration of ripe oocytes (atresia) during the spawning season. J. Exp. Zool. 284:343-354, 1999. Copyright 1999 Wiley-Liss, Inc.