Effects of Dietary Protein Levels on Growth Performance, Plasma Parameters, and Digestive Enzyme Activities in Different Intestinal Segments of Megalobrama amblycephala at Two Growth Stages

Abstract

An 8-week rearing trial was designed to estimate the dietary protein requirement and evaluate the effects of dietary protein on growth performance, plasma parameters, and digestive enzyme activities of blunt snout bream at two growth stages. Six practical diets were prepared to feed two sizes of fish (larger fish: initial weight of 153.69 ± 0.85 g; smaller fish: initial weight of 40.89 ± 0.28 g) with graded protein levels (26%, 28%, 30%, 32%, 34%, and 36%). Our results show that the final weight, weight gain (WG), and specific growth rate (SGR) of the fish initially rose to peak values and then declined as the dietary protein levels increased. The higher WG and SGR were recorded in the larger fish fed diets containing 30%, 32%, and 34% protein, and in the smaller fish fed a 30% protein diet, all significantly higher than those in the control group (p 0.05). The plasma total protein (TP) content was highest at both growth stages in fish fed a 30% protein diet (p 0.05). Protease activity in the fish foregut at both growth stages peaked in the 32% protein group (p 0.05). The dietary protein levels had no significant effect on lipase activity in the foregut, midgut, or hindgut, or on amylase activity in the foregut or midgut of the fish at the two growth stages (p > 0.05). However, hindgut amylase activity was highest in the control group of the smaller fish (p

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