| Abstract: | Oreochromis niloticus is an endemic species in the River Nile and represents the main object of fishery in the Nile Delta Lakes of which Lake Maryût is the smallest and most polluted. Due to current pollution problems, fish production in the lake greatly declined. Besides fish biology, this study considered a wide array of water databases in selected sites along the lake. Hydrologic and biologic data were compared to that of a reference fish hatchery. Water concentrations of ammonia, manganese, nickel, cadmium, lead and mercury proved hazardous to fish, whereas chromium, copper, iron, zinc, pH, alkalinity, hardness, phosphate, nitrate, and nitrite always fell within acceptable levels. Physiologic evaluation of O. niloticus pointed out improper growth, protein inadequacy, and functional impairment in fish inhabiting polluted sites, in particular the lake main basin. These were reflected by data of specific formulae as RNA/DNA and the relative RNA content (r) in cells of the liver and gill arches as well as by the relative mobilization of serum protein fractions. It seems, however, that growth competence is additionally affected by the stress impact exerted upon fish by massive population numbers in some cramped commercial ponds. |
