Production of protein hydrolysates from skipjack tuna (Katsuwonus pelamis) viscera as feeding attractants for Asian seabass (Lates calcarifer)

Skipjack tuna viscera hydrolysate (TVH) was produced by enzymatic hydrolysis using alcalase. A study of the effect of time and enzyme concentration was performed and formed the basis for preparing TVH with the desired degree of hydrolysis (DH). An enzyme to substrate ratio of 5gkg(-1) (TVH A1) and 16.4gkg(-1) (TVH A2) at pH 8.0 with a temperature of 50 degrees C, and hydrolysis time of 60min were found to be optimal conditions to obtain hydrolysis of 42.9% and 62.9%, respectively. Both TVH A1 and TVH A2 were analysed for chemical and amino acid composition and peptide size. The effectiveness of TVH at different DH as feeding attractants was estimated in a feeding trial at different inclusion levels. Ten experimental diets, including a fish meal-based reference diet, were fed to Asian seabass for 28days. Fish fed the diet supplemented with 30gkg(-1) of TVH A2, and the reference diet showed the highest feed intake (P<0.05). The growth performance of fish fed diets supplemented with TVH was slightly higher than those of fish fed the control diet, but the reference group showed a significantly higher growth rate (P<0.05). These findings suggest that the supplementation of feed with TVH that has been processed under suitable conditions can improve feed palatability and growth performance when utilizing alternative protein sources in Asian seabass diets.