Proline with or without hydroxyproline influences collagen concentration and regulates prolyl 4-hydroxylase α (I) gene expression in juvenile turbo (Scophthalmus maximus L.)

This study was conducted to investigate the effect of dietary proline (Pro), and Pro and hydroxyproline (Hyp) in combination on the growth performance, total Hyp and collagen concentrations of tissues, and prolyl 4-hydroxylase alpha(I) (P4H alpha(I)) gene expression in juvenile turbot feeding high plant protein diets. A diet containing 50% crude protein and 12% crude lipid was formulated as the basal and control, on which other two protein and lipid contents identical experimental diets were formulated by supplementing the basal with either 0.75% Pro (Pro-0.75) or 0.75% Pro and 0.75% Hyp (Pro+Hyp). Four groups of fish in indoor seawater recirculating systems, 35 individuals each, were fed twice a day to apparent satiation for 10 weeks. The results showed that dietary Pro and Hyp supplementation had no significant effect on growth performance and feed utilization of juvenile turbot (P > 0.05). Total Hyp and collagen concentrations in muscle were significantly increased when dietary Pro and Hyp increased (P < 0.05), and fish fed diet Pro+Hyp showed significantly higher free Hyp content in plasma than those fed other diets (P < 0.05). The expression of P4H a(I) gene in liver and muscle was significantly up regulated in fish fed diet Pro-0.75 in comparison with control (P < 0.05); however the gene was significantly down regulated in fish fed diet Pro+Hyp in muscle in comparison with fish fed diet Pro-0.75 (P < 0.05). It can be concluded that supplement of crystal L-Pro and L-Hyp to high plant protein diets did not show positive effects on growth performance of juvenile turbot, but enhanced total collagen concentrations in muscle.