The effect of dietary protein and total energy content on digestive enzyme activities, growth and survival of Litopenaeus setiferus (Linnaeus 1767) postlarvae

Abstract

The effect of dietary protein and energy content on the activity of digestive enzymes (total proteinases, trypsin, chymotrypsin alpha -amylase and lipase), and growth and survival of Litopenaeus setiferus postlarvae was investigated under controlled conditions. There was a clear relationship between the diet fed to the postlarvae, growth and survival. Highest weight gain (2110 +/- 96.7%) was obtained with a 400 g kg(-1) protein and low energy diet (13.9 kJ g(-1)) (P < 0.05). The optimal protein to energy ratio (P/E) estimated was 28.8 mg of protein kJ(-1). Good survival was obtained with low energy diets containing between 200 and 400 g kg(-1) protein and with high energy diets containing 300-500 g kg(-1) protein. Higher values for total proteinases, trypsin and <alpha>-amylase were obtained with the low energy, 400 g kg(-1) protein diet. Chymotryptic activity was considerably lower than that of other proteinases and lipase activity was too low to be reliably measured with the turbidimetric method employed. Total proteinase activity was significantly lower than in experimentally grown postlarvae. The alpha -amylase activity was at least two orders of magnitude higher in wild postlarvae than in animals fed with the best experimental diet. Protein requirement was related to total energy content of the diet: best growth and digestive enzyme activity coincide with the low energy, 400 g kg(-1) protein diet. These results suggest that dietary carbohydrates cannot spare protein because growth rates obtained with diets containing 200-300 g kg(-1) protein (337 and 226 g kg(-1) dextrin content, respectively) were significantly lowered.