Fish protein hydrolysate in diets of turbot affects muscle fibre morphometry, and the expression of muscle growth‐related genes.

The study was conducted to investigate the effects of fish protein hydrolysate (FPH) in diets for turbot on growth performance, muscle fibre morphometry, and the expression of muscle growth‐related genes. A control diet (FPH0) contained 0 g/kg FPH, and four experimental diets were formulated replacing fishmeal with FPH at levels of 45 (FPH4.5), 120 (FPH12), 180 (FPH18) and 300 (FPH30) g/kg. Fish fed the FPH12 and FPH18 diets had higher specific growth rate (SGR) than fish fed the FPH0 diet (p <.05), and a quadratic regression was found between SGR and dietary FPH level (p =.001, R2 =.677). Cross‐section area (CSA) and the length of sarcomere in the FPH12 group increased compared with the control group (p <.05), and a quadratic regression was observed between CSA and dietary FPH level (p =.006, R2 =.574) and between sarcomere length and dietary FPH level (p =.018, R2 =.788). An appropriate level of FPH down‐regulated myostatin 2 gene expression and up‐regulated proliferating cell nuclear antigen gene expression, while the expression of myogenic regulatory factors was not affected by dietary treatments (p >.05). To conclude, an appropriate level of FPH may improve muscle growth by regulating the expression of muscle growth‐related genes, and muscle microstructure and ultrastructure. [ABSTRACT FROM AUTHOR]