Some Physiological Studies One The Nile TilapiaIn Response To Stress Conditions

This study was performed in the Department of Physiology, Faculty of Vet. Med.,Zagazig University. A 150of male and female Nile Tilapia obtained from the National Center of Fish Research in Abassa, Sharkia Province, Egypt.The weight of the fish was between 70-110 gm/individual. The fish were divided into 3 equal groups : the first group was considered as control one, the fish of the second group wasexposed to hypoxia as stress factor, and the fish of the third group subjected to food deprivation. The experimentwas continued for 6 days. The fish put in glass aquariumcontained 25 fish and supplied with dechlorinated tap waterwhich stocked in large tanks 24 hours before using for evaporation of dissolved chlorine. One third of the water in each aquarium was daily exchanged with great attention forremoval of fish excreta and food residualsfrom the bottomof the aquarium. The fish left for one week before the beginning of experiment for adaptation.The water temperature was kept at ~7 ± 3 °C and the pHat 7-8 during the whole period of adaptation andexperimentation with natural photoperioAll aquaria were aerated using air pumps which supplied oxygen levels not less than 4 mg/lit., except the group which exposed to hypoxia as the oxygen level was 1.5 i 0.5 mg/lit. after removing the aeration from this group.The fish were fed once daily with balanced commercial ration in the form•of artificial pellets, at a rate of 0.5% of the