Different responses of grass carp (Ctenopharyngodon idellus) and black carp (Mylopharngodon piceus) to low-protein diets and subsequent recovery

An 8-week growth trial was designed to evaluate the effects of low-protein diets and subsequent recovery on grass carp (Ctenopharyngodon idellus) and black carp (Mylopharngodon piceus) in order to compare the compen-satory growth of the two species with different feeding habits. During the restricted period (weeks 1???4), grass carp were fed three kinds of isoenergetic and isolipid diets containing 32% (C, Control), 27% (LEP), and 22% (LP) protein individually, and black carp were fed diets containing 37% (C, Control), 32% (LEP) and 27% (LP) protein individually. In the recovery period (weeks 5???8), all fish were fed the control diets individually. The results showed that the protein restriction led to significantly lower feed conversion efficiency (FCE) and specific growth rate (SGR) for two species. In the recovery period, test group grass carp had similar protein retention efficiency (PRE) and FCE to the control group and had significantly lower final body weights (FBW), succinate dehydrogenase (SDH), significantly higher lactate dehydrogenase (LDH), and aspartate aminotransferase (AST) than the control group. The test group black carp had significantly higher PRE and FCE than the control group, and the LEP group had similar FBW, LDH, AST, and alanine aminotransferase (ALT) to the control group and had significantly lower pyruvate kinase (PK) and SDH. The study reveals that grass carp increase gluconeogenesis and fail to increase feed utilization efficiency significantly, thus failing to obtain compensatory growth. Black carp decrease the carbohydrate catabolism and tricarboxylic acid (TCA) cycle, increase feed utilization efficiency significantly and get compensatory growth in the LEP group. Black carp have better compensatory growth ca-pacity than grass carp, and the different capacities may be related to the different nutrient utilization strategies of the two species.