Dietary protein requirement of juvenile red spotted grouper (Epinephelus akaara)

Abstract

An 8-week feeding trial was conducted to assess the dietary protein requirement of juvenile red spotted grouper (Epinephelus akaara). Six semi-purified diets were formulated with varying crude protein (CP) level (ranging from 32.20% to 61.85%). Each diet was given to triplicate groups (20 fish per group, 7.88±0.04g per fish). The growth of juvenile E. akaara was significantly affected by the different dietary CP levels (P<0.05). The results of feeding trial showed that fish fed diet with 50.45% CP exhibited the highest weight gain (WG) value. Both quadratic and linear responses were observed on the feed efficiency (FE) and protein efficiency ratio (PER) as the level of dietary CP increased (P<0.05). The lowest feed efficiency (FE) was noted in diet containing 32.20% CP treatment. Moreover, daily feed intake (DFI) was highest in fish fed 32.20% CP diet. There were quadratic and linear responses in viscerosomatic indexes (VSI) and hepatosomatic index (HSI) values with dietary CP increased (P<0.05). Fish fed 32.20% CP diet obtained the highest plasma aspartate transaminase (AST) and alanine transaminase (ALT) activities. Fish fed a diet with the lowest CP obtained relatively lower energy retention (ER), lipid retention (LR) and nitrogen retention (NR). The protein content in the dorsal muscle and liver was significantly affected by the different CP levels (P<0.05). Based on the second polynomial regression analysis of WG, the dietary protein requirement for E. akaara was estimated to be 50.83%.Statement of relevanceThe main aim of this study is to quantify the optimum amount of dietary protein for juvenile red spotted grouper (E. akaara). The research outcomes will develop formulated diets for E. akaara and will have good potential for being commercialized.