The impact of changing dietary Na/K ratios on growth and nutrient utilisation in juvenile African catfish, Clarias gariepinus

The effects of dietary Na/K ratios on feed intake, growth, nutrient utilisa tion. plasma and body mineral concentration in juvenile African catfish wer e investigated. Four Na/K ratios, 0.2, 0.7, 1.5, 2.5 (mmol/mmol). were test ed in a randomised experimental design with three replications in each trea tment. Juvenile African catfish (n = 360) with a mean initial body weight o f 42.9 g were used. The experiment was conducted in 12 (70 1) aquaria with a biofilter and recirculating water supply system. Dietary Na/K ratios were obtained by altering levels of Na2CO3 and K2CO3. Feed was provided manuall y twice a day to satiation. Feed consumption was not influenced by the mine ral composition of the diets. Growth. protein retention, nitrogen and energ y utilisation efficiency increased quadratically, body dry matter, fat, nit rogen and energy content increased in a linear or quadratic manner with inc reasing dietary Na/K ratio. Feed conversion and percentage of energy retent ion as protein decreased in a quadratic manner. Potassium and chloride conc entrations and the ratios between Na/K, Na/Cl and K/Cl in the body remained constant among treatment groups at the end of a 4-week feeding period. In conclusion, excess K in the diet depresses growth and nutrient utilisation efficiency, reduces body fat and protein deposition. The dietary Na/K ratio of 1.5 to 2.5 produced the best growth of African catfish. (C) 2001 Elsevi er Science B.V. All rights reserved.