Document Type : Original Article
Authors
1
Central Laboratory for Aquaculture Research-Agriculture Research Center-Agriculture Ministry
2
Agriculture Faculty-Cairo University
Abstract
Two trials were conducted in Animal Physiology Lab., Faculty of Agriculture; Cairo University from May to November, 1999 to quantify and evaluate the growth performance of male Nile Tilapia (Oreochromis niloticus) affected by physiological responses to thermal and salinity conditions in aquaria. The experiments were conducted either on fry (for 30 days) or fingerlings (for 42 days). The experimental study incorporated six treatments (T1-T6) between two temperature degrees (28.59, 33°C for fry and 23.91, 33°C for fingerlings) and three salinity levels fresh brackish and sea water (0.1, 15 and 30 ppt, respectively). Both dissolved oxygen (DO) and pH did not reach critical values for both fry and fingerlings. The daily weight gain of fry was greater (0.145 g/ fish/day) in fresh water than in brackish water (0.041 g/fish/ day). The lowest daily gain was in seawater (0.037 g/fish/day), the differences were significant (p<0.05). After 30 days from starting the experiment, the daily weight gain of finger- lings showed equal means (0.1955 and 0.196 g/ fish/day) in both fresh water and brackish water, compared to half value in seawater (0.096 g/fish/ day). The fish could not tolerate the high temperature and/or concentrated salinity (seawater 30 ppt) further than 30 days. It was obvious that the fish chemical constitutions were not affected by temperature or salinity as well as their interactions. The concentrations of Na+, K+, P--- and Cl- in blood plasma were, 477.47, 40.44, 0.88 and 249.09 mg/dl, respectively, under fresh water (0.1 ppt salinity). In the sea water (30 ppt salinity) the values were 490.97, 34.37, 1.24 and 300.5 mg/dl, while in brackish water were 456.45, 31.99, 1.31 and 337.59, respectively. The ions (Na+, K+ and P---) besides Ca++ and Mg++ in the fish tissue (dried body) were 22.95, 0.21, 3.36, 41.18 and 2.27 mg/g respectively in fresh water (0.1 ppt), while in seawater (30 ppt) the values were 18.1, 0.19, 3.38, 42.09 and 2.31 mg/g respectively. Fish in seawater treatments had the highest concentration of aldosterone hormone in blood plasma with the average of 0.55 pg/ml. while fresh and brackish water treatments in- duced lower and similar concentrations of aldosterone, 0.46 and 0.48 pg/ml, respectively after 30 days.
Main Subjects
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