Effects of feeding on ammonium excretion and growth of the African catfish (Clarias gariepinus) fry

The study was aimed at assessing the effects of different protein contents and feed rations on the growth and metabolic rate of African catfish (Clarias gariepinus) kept in a recirculation system. The fish were fed every day, between 8.00 and 20.00 hours, three feeds (A, B, and C) differing in their protein content (about 36, 40, and 46%, respectively). The daily feed ration, expressed by the amount of consumed protein, ranged from 2 to 4% of the stock weight. The highest growth rate (SGR = 5.21%) was typical of the fish receiving feed B at the 4% level while the lowest feed conversion ratio (FCR = 1.21) was recorded in the fish receiving the same feed, but administered at the 2% level. The latter treatment also showed the best protein and energy retention levels (32.33 and 27.23%, respectively). In all the treatments, an increase in the mean individual weight was accompanied by a drop in the rate of ammonia nitrogen release. The lowest values (0.0094-0.0071 mg/g fish weight/h) were found in the fish receiving feed C at the 2% level, the highest values (0.0337-0.0183 mg/g fish weight/h) being typical of the fish administered feed A at the 4% level. The maximum ammonia nitrogen release in all the experimental treatments was found to occur between 18.00 and 21.00 hours.