Dietary hydroxyproline improves the growth and muscle quality of large yellow croaker Larimichthys crocea

The present study was conducted to estimate the effect of dietary hydroxyproline (Hyp) on growth, muscle texture and collagen content of large yellowcroaker. Six isonitrogenous and isolipidic practical dietswere formulated to contain graded levels of Hyp (0.17%, 0.26%, 0.33%, 0.50%, 0.69% and 0.86% of dry matter). Fish with similar size (initial body weight, 189.87 +/- 0.89 g) were distributed into 18 floating net-cages (1.5 m x 1.5 m x 2.0 m). Each diet was hand-fed to triplicate groups of large yellow croaker for 82 days. The results showed that the specific growth rate (SGR) of fish fed diet with 0.33% of Hyp was significantly higher than those fed with the basal diet (0.17% Hyp) (P < 0.05). No significant differences were found in survival rate, viscerosomatic index, hepatosomatic index, condition factor and feed intake among all treatments (P > 0.05). Protein efficiency ratio and feed efficiency significantly increased with increasing levels of dietary Hyp up to 0.33% (P < 0.05). Moisture and crude lipid contents inmuscle showed no significant difference among all treatments (P > 0.05), while crude protein was significantly improved by dietary Hyp (P < 0.05). Significant decreases were observed inmuscle liquid loss and water loss with increasing levels of dietary Hyp (P < 0.05), while little variation was detected in lipid loss (P > 0.05). A statistically significant difference was observed inmuscle pH with dietary Hyp (P < 0.05). Except for the cohesiveness and adhesiveness, all other analyzed texture properties including hardness, springiness, chewiness in muscle were significantly affected by dietary Hyp. Alkaline-soluble Hyp reached to the highest value inmuscle when fish were fed diet with 0.69% of Hyp. The highest value of the total Hyp content inmuscle was found in the treatment with 0.86% of dietary Hyp (P < 0.05). No significant difference was detected inmuscle alkaline-insoluble Hyp, salt-soluble protein and water-soluble protein (P > 0.05) among all treatments. Pyridinium crosslink (PYD) inmuscle increased with increasing dietary Hyp content up to 0.69% (P < 0.05). Hardness, springiness and chewiness showed a high and positive correlation with alkaline-soluble Hyp, total Hyp and PYD, and negative correlation with liquid loss and water loss. It was concluded that dietary Hyp could benefit fish growth, promote the formation of collagen, and thereafter influence muscle quality of large yellowcroaker. Using the broken-line models based on SGR and the total Hyp content in muscle, the optimal dietary Hyp content for large yellow croaker were estimated to be 0.33% and 0.61%, respectively. Statement of relevance: This study is not a test of commercial aquaculture. (C) 2016 Elsevier B.V. All rights reserved.