Carbohydrate utilization by rainbow trout is affected by feeding strategy

A 16-wk experiment was conducted to compare the utilization of four carbohydrates by rainbow trout (Oncorhynchus mykiss) fed either continuously or four meals daily. The carbohydrates were glucose, maltose, dextrin and raw cornstarch, and were included at 32 g/100 g diet. Average initial body weight of the fish was 5.5 g, and fish were fed at a restricted rate of 2.0% body wt/d. Significant (P < 0.05) interactions between feeding strategy and carbohydrate were observed only for specific growth rate, final body weight, feed efficiency, and protein and energy retained. These measurements as well as whole-body moisture and lipid concentrations were also significantly higher in the continuously fed trout than in the meal-fed trout. Liver weight:body weight ratio, liver glycogen concentration, and liver lipogenic enzyme activities generally were higher in the continuously fed trout than in the meal-fed trout. Trout fed the glucose diet and those fed the maltose diet had higher specific growth rates, final body weights, feed efficiencies, energy retained, and whole-body and visceral moisture and lipid concentrations than those fed the starch diet. Trout continuously fed the glucose and maltose diets also had higher glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities than those continuously fed the starch diet. The higher protein and energy retained and the higher lipogenic enzyme activities in the continuously fed fish compared with the meal-fed fish showed that in trout growing slowly due to a restricted ration, continuous feeding improved the carbohydrate utilization and increased lipid storage by enhancing lipogenesis.