Effect of dietary replacement of fish meal by poultry by-product meal on the growth and hepatic health in loach (Paramisgurnus dabryanus)

Our objective was to systematically evaluate the impact of substituting fish meal (FM) with poultry by-product meal (PBM) in fish feed on the growth and hepatic health of loach. Six diets with different levels of PBM (0 %-PBM0, 10 %-PBM10, 30 %-PBM30, 50 %-PBM50, 70 %-PBM70 and 90 %-PBM90 were formulated. After 8 weeks feeding trial, the highest weight gain (WG) was observed in 55 % PBM replacement ratio. Meanwhile, the lowest feed conversion ratio (FCR) were observed in 41.56 % PBM replacement ratio. In addition, dietary PBM induced hepatic oxidative stress including increasing the activity of aminotransferase from PBM0 to PBM50 group, whereas the activity of those enzymes was decreased from PBM50 to PBM90 group. Meanwhile, histological analysis showed that the lipid vacuoles in the liver were increased from PBM0 to PBM50 group, then decreased from PBM50 to PBM90 group (P< 0.05). Moreover, primary bile acid biosynthesis was the only one pathway enriched in top 20 significant pathways by transcriptomic and metabolomic analysis. Specifically, the key bile acid synthesis gene CYP7a1 was down-regulated, while CYP7b1 evinced an up-regulated pattern in PBM50 group compared to PBM0 group. In short, the PBM replacement ratio of up to 50 % in diets was appropriate for rearing loach, while higher PBM replacement ratio resulted in extremely oxidative stress in the liver.