Discussion and conclusions
O. niloticus is known to tolerate high temperatures. It cannot tolerate for a long period water temperature between 10 and 15 °C ( Ballarin and Hatton, 1979), and does not survive below 10 °C ( Chervinski and Lahav, 1976). The optimum temperature for feeding, growth and reproduction is between 22 and 30 °C ( Caulton, 1982), while good growth was recorded in the upper portion of this range ( Hauser, 1977). Thus, at higher or lower temperatures, feeding and growth rates are reduced, and at 20 °C or less, feeding and growth are stopped ( Caulton, 1982).