Fish require relatively high dietary protein levels when compared with other farm animals. Because of the high price of protein and the environmental effects of nitrogen discharge, the protein sparing effect of non-protein energy, in the form of lipids and carbohydrates, received considerable attention. Decreasing the protein-energy ratio in the diet does increase the protein efficiency in fish, but at the expense of increased body lipid levels. In mammals and birds a negative effect of adiposity on feed intake has been observed, mediated by the hormone leptin. Leptin has recently been isolated in a number of fish species and also a role of adiposity in feed intake regulation has been found in some (other) fish species. To examine the effects of dietary protein-energy ratio and adiposity on feed intake of African catfish, Clarias gariepinus at 25°C a three-phase experiment was conducted. In the first phase of 21 days three groups of catfish were created of comparable bodyweight ( 27-35g) but differing in body lipid content by feeding them equal amounts of protein of three diets with protein-energy ratios of 33 (H), 27 (M) and 18 (L) mg P kJ-1. In the second phase of 27 days a cross-over design was used by dividing each group in three and feeding them to apparent satiation twice daily with either the diet they where fed in the first phase or one of the two other diets, giving the following combinations: HH, HM, HL, MH, MM, ML, LH, LM and LL. In the third phase this procedure was repeated for the fish that had remained on their first-phase diets, giving combinations HHH, HHM, HHL, MMH, MMM, MML, LLH, LLM and LLL. Al combinations where tested in duplicate. Feed intake was recorded daily. Average body weight and body composition where determined at the end of phase 1, 2 and 3. No direct effect of diet on feed intake could be demonstrated as fish with the same dietary background consumed equal amounts of the three diets during the first 8-10 days after cross-over. Over the whole cross-over periods both the diet before and after cross-over significantly affected feed intake as well as body lipid content. The effect the diet after cross-over was more dominant as shown by a larger effect size. Feed intake of fat fish was 25% lower (17% as energy) than that of lean fish. Growth rate was decreased by 37% and feed conversion was increased by 20%. We conclude that for African catfish feed composition affects feed intake largely through effects on body lipid content. For this extremely fast growing species such an effect could be observed within 10 days after a change in feed composition.
|Publication status||Published - 2008|
|Event||XIII International Symposium on Fish Nutrition and Feeding - |
Duration: 1 Jun 2008 → 5 Jun 2008
|Conference||XIII International Symposium on Fish Nutrition and Feeding|
|Period||1/06/08 → 5/06/08|