The effect of dietary hydroxyproline supplementation on salmon (Salmo salar L.) fed high plant protein diets

Plant protein sources normally used in aquaculture feed contain by nature low levels or no hydroxyproline. To evaluate the potential effect of dietary inclusion of hydroxyproline (hyp) in high plant protein diets, a regression design was carried out in an 88 days growth experiment with salmon. All experimental diets were equal with regard to chemical composition and level of the various ingredients, the only difference was the addition of crystalline hyp. Fish meal inclusion was 185 g kg(-1). Five different inclusion levels of hyp were used in duplicate tanks; no addition, 0.7, 1.4, 2.8 and 5.6 g kg(-1). One control diet was run in triplicate, added 2.8 g kg(-1) crystalline proline (pro). Growth was significantly improved by dietary hyp addition in a polynomial regression, indicating maximum growth at 2.9 g kg(-1) added hyp in which weight gain was improved by 14%. No effect was observed on feed intake or feed efficiency. Analysis of the whole vertebral column showed significantly increased hyp content, and lower ash content of vertebrae in fish fed increased dietary hyp inclusion. No difference was observed in fish fed diets with no addition and those fed dietary supplementation of pro. The results indicate that the anabolism of hyp may be limiting and that dietary hyp supplementation improved growth and vertebrae development or that hyp has some specific physiological or biochemical function. This information may be important in work to find replacement of fish meal in a sustainable growing global aquaculture industry and in work to prevent vertebrae disorders in tanned fish. This work suggests that a focus on hyp should be included in studies to evaluate amino acid requirements and studies of the impact of various protein sources for fish feeds. (c) 2008 Elsevier B.V. All rights reserved.