Replacing fishmeal protein with blended alternatives alters growth, feed utilization, protein deposition and gut micromorphology of humpback grouper, Cromileptes altivelis

Abstract

This research aims to investigate the effects of different dietary fishmeal (FM) protein replacements by blended alternative proteins on growth, feed utilization, protein deposition and gut micromorphology of humpback grouper, Cromileptes altivelis. Five isoenergetic (14.23 kJ/g, dry matter), isoproteic (48.91 %, dry matter) and isolipidic (10 %, dry matter) experimental diets were formulated, with 0 % (R0), 21 % (R21), 42 % (R42), 63 % (R63) and 84 % (R84) FM protein being replaced by blended alternative proteins which consisted of soybean protein isolate (SPI), poultry by-product meal (PBM), hemoglobin powder (HP). Triplicate groups of fish (mean initial body weight: 6.50 ± 0.17 g, 12 fish/group) were manually fed each diet to apparent satiety twice daily for 8 weeks. Results showed that different FM protein replacements by the blended proteins significantly influenced percentage weight gain (WG %), daily feed intake (DFI), feed conversion ratio (FCR), protein efficiency ratio (PER) and protein productive value (PPV) of fish. Fish fed R84 had the lowest WG %, PER and PPV among all experimental groups. The quadratic broken-line regression analysis of WG % indicated that the maximum FM protein replacement level by the blended proteins was 67.0 % of dry matter. Fish fed R84 had lower expression of growth hormone (GH), growth hormone receptor (GHR), insulin like growth factor-I (IGF-1), target of rapamycin (TOR) and S6 kinase 1 (S6K1) than fish fed other diets. General control nonderepressible 2 (GCN2) and CCAAT enhancer binding protein β (C/EBPβ) showed higher expression in the R84 group compared to those in other groups. The villous height (hV), villous width (wV) as well as enterocyte height (hE) of gut were also affected by different experimental treatments, with the R84 group having lower values compared to other groups. Generally, 67.0 % of dietary FM protein could be replaced by a blend of SPI, PBM and HP proteins without negatively influencing the WG % of humpback grouper.