Gastric and intestinal evacuation of a pelleted meal in rainbow trout (Oncorhynchus mykiss) and Mozambique tilapia (Oreochromis mossambicus): a comparison

Knowledge of gastric and intestinal food passage rates are useful to both the fish culture industry and for estimates of a species daily rations in the wild. This study compared gastric and intestinal food passage in two very different species, Mozambique tilapia Oreochromis mossambicus and rainbow trout Oncorhynchus mykiss . Both species were fed a common pelleted meal. The effects of meal size were investigated at temperatures at which each of the species is commonly cultured. Also, the two species were compared at a common water temperature. In addition, the use of chromic oxide as a measure of food passage through the intestine was evaluated. Meal size did not affect gastric emptying times in either species when expressed as a proportion of the meal consumed regressed on the natural log of time since fed. Gastric emptying in tilapia required 24 h at 25 °C and more than 45 h for trout at 13 °C. Chromic oxide was a good indicator for the progression of the meal through the intestinal tract in both species. Meal size did not affect intestinal emptying. Tilapia required 45 h compared with 65 h for trout. Gastric and intestinal emptying at 19 °C did not differ between the two species.