A Trial to Culture Yellowtail with Non-fishmeal Diets

The purpose of this series of study was to develop a non-fish meal diet for yellowtail, and feeding trials were conducted to examine the utilization of test diets formulated with soy protein concentrate, defatted soybean meal, corn gluten meal, and meat meal as protein sources. Juvenile (13g on average) and young (130g on average) yellowtail were fed experimental non-fish meal diets with these ingredients for 52 days and 75 days, respectively, and growth and feed performance parameters were compared with the fish meal-based control diet. The experimental non-fish meal diets were of poor palatability to the juvenile fish, and this may be related to the inferior feed performance and growth compared to the control. Young fish fed the experimental diets showed active feeding, and normal growth was sustained for the first 46 days of feeding, but thereafter stagnant growth, poor feed gain ratio, and high mortality were observed irrespective of the dietary treatments. Moreover, at the end of the experiments, both juvenile and young fish fed the non-fish meal diets revealed the green liver symptom and poor blood characteristics, indicative of the abnormal physiological status. Thus, these results proved that non-fish meal diets used in this study were not efficient in maintaining normal growth and health of juvenile and young yellowtail for a long rearing period. The poor feed performances is thought to be linked with the appearance of green liver, but its mechanism remains unknown.