The effect of dietary salt on growth of Clarias gariepinus is examined in the first study. In the second study an attempt is made to underscore the main changes in body muscle composition of Clarias gariepinus during growth. The effect of dietary sodium chloride on the growth performance, cannibalism and survival of first-feeding African catfish (Clarias gariepinus) was assessed in a 16 days experiment. A commercial diet containing 0,5% dietary NaCl was supplemented with various levels of dietary NaCl in order to obtain eight test diets for the experiment. Total amount of dietary salt in the test diets was then brought to: diet 1 (0,5%NaCl), diet 2 (0,7% NaCl), diet 3 ( 0,9%NaCl), diet 4 (1,1%NaCl), diet 5 (1,3%NaCl), diet 6 (1,5%NaCl), diet 7 (1,7%NaCl) and diet 8 (1,9%NaCl). The eight test diets were randomly assigned to sixteen 40 l glass aquaria in duplicate. An open recirculation culture system was used. Growth performance was determined on the basis of growth rates and food conversion ratio. Effects of salt on growth performance was highly significant (p<=0,0001). Larvae fed diet 3 (total % NaCl=0,9) and 4 (total % NaCl=1,1) gained significantly higher mean weights than those fed the 0,5% NaCl control test diet (p<0,05, p<0,01 respectively). Larvae fed test diets with higher salt loading (1,5 - 1,9% total NaCl) showed poor growth performance. Food conversion ratio was lowered by optimal dietary NaCl supplementation in diet 3 (0,9% salt) and diet 4 (1,1% salt). Survival was low in all treatments due to the fact that dry feed was used to prepare test diets instead of live feed. But higher survivals were, however, recorded for the larvae fed 0,9%, 1,1% and 1,3% salt diets. The highest specific growth rate (13,30% day-1) was recorded for the larvae fed 1,1% NaCl test diet. Since 1,1% dietary sodium chloride concentration in dry feed promoted maximum growth in the experimental Clarias gariepinus larvae it is hereby suggested to be the "optimal" NaCl concentration for maximum growth performance of the larvae of this fish species. An evaluation of the changes in body muscle composition of Clarias gariepinus during growth was performed in a 201 days experiment. One hundred Clarias gariepinus fingerlings were reared in two separate culture tanks of 60 l volume in a flow-through system from 1,08g to 383g mean body weight. Protein levels were found to increase with live body weight gain. Fat was found to have no relationship with changes in live body weight. Ash and moisture contents did not change much during the development of the fingerlings. Dry matter (%DW) and ash-free dry weight (%AFDW) were positively related to changes in body weight of the fish. Protein content in C. gariepinus is higher in bigger fish than in smaller fish during fingerling stage. Changes in the amount of protein content, dry matter (DW) and ash-free dry matter (AFDW) in the body muscle tissue of C. gariepinus can be described in function of one another. Fat content in C. gariepinus is considerably low at the fingerling stage. It continues to be low throughout the fingerling stage and is independent of changes in live body weight. % Protein (P) and % ash contant (A) in body muscle of C. gariepinus are related to live body weight (BW) (g) as follows: % P = 13,80 BW0,058% A = 2,95 BW-0,19 |
