Investigation of growth and flesh quality of juvenile rainbow trout (Oncorhynchus mykiss) fed with different performance promoters

This research gives account to the effect of different growth promoters namely Monocalcium Phosphate (MCP) and OPTIPHOS as phytase enzyme to the growth performance, whole-body nutrient composition of Rainbow trout (Oncorhynchus mykiss). The effects of histological changes in the fish intestine were also investigated. Feeding trial used 750 juvenile rainbow trout fish (Oncorhynchus mykiss, 32,57 ± 0,36 g and 13,67 ± 0,66 cm) for 90 days from 02 July to 28 September 2019. Five iso-nitrogenous (48% crude protein) and iso-lipidic (16% crude lipid) diets were prepared. Positive control (PC) diet was mixed with 21g/kg MCP without the addition of enzymes. Negative control (NC) diet contained neither MCP nor enzyme. Other diets were mixed with OPTIPHOS® as phytase enzyme at the ratios 0,15g/kg feed (NC750 OPTI), 0,30g/kg feed (NC1500 OPTI) and 0,60g/kg feed (NC3000 OPTI) accordingly. Fish fed with different levels of MCP and OPTIPHOS showed significant improvements in feed consumption and growth performance (P<0.05). Moreover, feed conversion ratio, viscero-somatic index, and hepato-somatic index were significantly decreased by these supplementations (P<0.05). Economically, calculated price of formulated feeds per kilogram for feeding trials ranged 7.168 – 7,242 TL, consequently, the economic conversion (ECR) was significantly reduced by MCP and OPTIPHOS supplementations (P<0.05). Economic profit index of fish (EPI) was also significantly improved with MCP and OPTIPHOS supplementations (P<0.05). Fish fed with MCP and OPTIPHOS showed significant improvement in whole-body crude protein, crude lipid, ash, liver lipid content, bone ash content and bone phosphorous contents (P<0.05). Supplementation of MCP and OPTIPHOS enzymes in fish did not alter the general histopathological morphology of intestinal mucosa, however, the morphometric attributes were significantly improved (P <0.05). MCP and OPTIPHOS doses significantly improved the villus length, decreased crypt depth, improved villus length to crypt ratio and increased villus surface area (P<0.05). Conclusively, the supplementations of MCP to improve the phosphorous content in feeds and OPTIPHOS to improve phosphorous content through degradation of phytate and phytic acid have positive potential to fish productivity and to the profitability of rainbow trout aquaculture. Whereby, effects of experimental feeds to the fish been considered, 750 OTUkg-1 OPTIPHOS is the most effective dose for juvenile rainbow trout.