Dietary phytase and xylanase improves growth performance, intestinal morphometric properties, and metabolic gene expression in rainbow trout (Oncorhynchus mykiss)

Abstract The aim of this study was to investigate the effects of phytase and xylanase enzymes in diets with high plant proteins on growth, nutritional composition, intestinal morphology, and metabolic gene expression in rainbow trout, Oncorhynchus mykiss . A total of 900 fish were randomly assigned in triplicates (50 fish weighing 31.61 ± 0.32 g per tank) to each of the 6 experimental diets. Dietary treatments included two positive control (PC) groups: PC1, formulated with 40% fish meal (FM), and PC2, formulated with approximately 60% plant proteins (PPS) and 1% monocalcium phosphate (MCP). The negative control (NC) was prepared with 60% PPS. The other three experimental groups were prepared as follows: PC2 + EPU (6000 EPU xylanase), NC + MIX1 (1500 OTU phytase + 6000 EPU xylanase), NC + MIX2 (3000 OTU phytase + 6000 EPU xylanase). At the end of the experiment, weight gain in PC2 + EPU, NC + MIX1, and NC + MIX2 was significantly increased by 11.30%, 8.22%, and 4.96% compared to PC1, respectively ( P < 0.05). Feed intake (FI) and feed conversion ratio (FCR) were significantly reduced in fish fed the NC diet compared to other groups. Phytase and/or xylanase supplementation in PC2 + EPU, NC + MIX1, and NC + MIX2 diets improved FCR, viscerosomatic index (VSI), hepatosomatic index (HSI), whole-body ash, bone ash phosphorus (P) contents, and intestinal villus morphometric characteristics ( P < 0.05). The addition of phytase and/or xylanase to PC2 + EPU, NC + MIX1, and NC + MIX2 diets increased profitability by reducing feed price and economic conversion ratio ( P < 0.05). Moreover, PC2 + EPU, NC + MIX1, and NC + MIX2 diets significantly upregulated the expression of intestinal nutrient uptake and transport genes, namely SLC4 A11 and ATP1 A3 A , and phospholipid hydrolysis genes PG12 A ( P < 0.05). Finally, the addition of phytase and xylanase to plant-based diets improved growth performance and intestinal morphology in juvenile rainbow trout and upregulated the expression of genes responsible for lipid hydrolysis, nutrient uptake, and transport.