Effects of feeding time, water temperature, feeding frequency and dietary composition on apparent nutrient digestibility in rainbow trout Oncorhynchus mykiss and common carp Cyprinus carpio

A series of experiments was conducted to evaluate the effects of feeding time (daytime vs nighttime feeding), dietary fat content (8 and 20%), feeding frequency (trout 1-3 times/day, carp 2-7 times/day), water temperature (trout 18 and 11 degrees C, carp 25 and 17 degrees C), on the apparent nutrient digestibility in rainbow trout and common carp. The feeding time had little effect on the macronutrient digestibility in both species. In trout, starch digestibility decreased with the decrease of water temperature and with increase of feeding frequency, but in carp, increase of the feeding frequency markedly decreased the macronutrient digestibility and phosphorus absorption of the high fat diet. Fat digestibility of the beef tallow diet decreased relative to the pollock oil diet in carp, without affecting the phosphorus absorption. Inclusion of raw starch, the digestibility of which was lower than that of gelatinized starch, increased the phosphorus absorption in carp. These results suggest that reduction of water temperature and increase of feeding frequency notably decreased starch digestibility in trout while in carp, the effects of feeding frequency and water temperature on macronutrient digestibility and phosphorus absorption are notable for a high fat diet.