THE EFFECT OF REDUCED CRUDE PROTEIN-CONTENT AND OF AMINO-ACIDS APPLICATION IN AFRICAN CATFISH (CLARIAS-GARIEPINUS) FEED MIXTURES UPON CRUDEPROTEIN AND FAT RETENTION IN FISH BODY

In the course of 10-week aquarium experimental African catfish culture , the effects were investigated of reduced crude protein content in fe eds and of amino acids (lysine, methionine and threonine) application upon crude protein and fat retention in fish body. In isoenergetic mix tures (gross energy content 16.5 kJ.g(-1) feed), the feed with 45% cru de protein (K) content served as control; whilst crude protein content in the following 6 feeds was reduced to 40 (1), 35 (2) and 30% (3). E ach of variants with reduced crude protein content was fortified with amino acids at the level of control (1A, 2A, 3A). It was found that cr ude protein retention in the body of fish fed mixtures 1, 1A, 2A and 3 A was higher in absolute values than in control treatment. In spite of the statistical insignificance of the differences, the increase of re tention by 1% implies reduced loading of water environment, namely by 1.6 g of pure nitrogen when feeding 1 000 g of dry matter of crude pro tein. The application of amino acids increased the crude protein reten tion relatively by 3 and 5% (2A and 3A respectively). The fat retentio n in the carcass of fish fed feeds with reduced crude protein content was always higher in comparison with control (45% crude protein). Amin o acid supplementation also increased fat retention in fish body. Fat retention in catfish carcass was highly significantly higher (P < 0.01 ) in comparison with crude protein retention. Reduced content of crude protein in catfish feed mixtures simultaneously supplemented with ami no acids reduces the nitrogen loading of water environment.