Effects of dietary enzymatic hydrolyzed three different tuna by-products as the fishmeal replacer in juvenile rainbow trout (Oncorhynchus mykiss)

Abstract

A feeding trial was conducted for 7 weeks to evaluate the effects of dietary enzymatic hydrolyzed three different tuna by-products on growth and non-specific immune responses of juvenile rainbow trout (Oncorhynchus mykiss). A basal commercial diet was formulated with 50% fishmeal (FM) used as a control diet (CONT), and seven other diets containing different levels and types of tuna by-products. Four diets were formulated by using enzymatic hydrolyzed tuna backbone by-products; TBB12.5, TBB25, TBB37.5 and TBB50 replacing FM 12.5%, 25%, 37.5% and 50% respectively. Two diets were formulated replacing 25% FM by the enzymatic hydrolyzed tuna intestine (TIB25) and head & fin (THFB25) by-products and a diet was formulated by using tuna commercial by-products (not hydrolyzed) replacing 25% FM (TB25). Fish averaging 4.87±0.05g (mean ±SD) fed with 3-4% of wet body weight of 8 experimental diets with triplicate groups. At the end of the feeding trial, weight gain and specific growth rate of fish fed CONT and TIB25 were significantly higher (P<0.05) than those of fish fed TBB50. However, there were no significant differences (P>0.05) among fish fed CONT, TBB12.5, TBB25, TBB37.5, TIB25, THFB25 and TB25. Non-specific immune responses as lysozyme and SOD (superoxide dismutase) activities were within the acceptable ranges in all dietary treatments with a little variation. The current price of FM, TBB, TIB, THFB and TB were 1,600₩/kg, 1000₩/kg, 1000₩/kg, 1000₩/kg and 1,400₩/kg respectively. Therefore, these results indicated that FM could be replaced up to 37.5% by enzymatic hydrolyzed tuna backbone by-products (TBB37.5) in the diets of juvenile rainbow trout without any negative effects on growth, feed utilization or carcass composition of fish.