Soybean dreg pre-digested by enzymes can effectively replace part of the fishmeal included in feed pellets for rearing gold-lined seabream.

The present study aimed to formulate diets using soybean dreg to replace part of fish meal (30% and 60%) and to incorporate dietary supplement to the diets with papain to promote fish growth and decrease total cost of feed formulations for gold-lined seabream (Rhabdosargus sarba). In Experiment 1, papain was used to supplement feeds containing soybean dreg to replace part of the fish meal. In Experiment 2, bromelain and a microalgae supplement were used to supplement feeds containing soybean substitutes as a replacement of the fish meal. Results from Experiment 1 indicated that the growth performance of fish fed diets with up to 60% replacement of fishmeal with soybean residues predigested with papain were not significantly different (p > 0.05) from the control (a formula developed by Agriculture, Fisheries and Conservation Department (AFCD), which contained 49.4% fishmeal, 45.2% raw trashfish, 4.9% alpha starch and 0.5% vitamin premix). It indicated that plant protein predigested with a small amount of enzyme supplement (e.g. papain) can be used to replace fish meal in traditional fish diets, and the cost could subsequebtly be reduced. In Experiment 2, the diets containing bromelain, soybean dreg pre-digested with bromelain and supplemented with microalgae resulted in significantly better growth performance than other diet groups. Results from the present study suggested that predigesting soybean dreg with enzymes could replace up to 60% fishmeal in the moist pellets while achieving economic benefits.