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 (13 g on average) and young (130 g on average) yellowtail were fed experimental non-fish meal diets with these in gredients for 52 days and 75 days, respectively, and growth and feed performance parameters were com pared 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 ex perimental diets showed active feeding, and normal growth was sustained for the first 46 days of feed ing, 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 ab normal physiological status.Thus, these results proved that non-fish meal diets used in this study were not efficient in maintain ing 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.Key words:non-fish meal diets, alternate proteins, yellowtail, green liverThough the present total production of animal feeds in Japan is estimated to be around 25 million t, the quantum of fish meal being employed in formulations stands at a meager 1.2%. In sharp contrast, out of the 500,000 t of fish feed produced during 1996 in Japan, the proportion of fish meal was about 56%, a manifold higher than that of other animal feeds.A recent rapid decline of the sardine catch in Japan has resulted in a shortage of fish meal supply for the feed indus try, prompting reliance on imported fish meal. To over come this shortfall, efforts are now being directed to find ing alternative protein sources of good nutritional value as a substitute for the expensive fish meal component in prac tical diets. The development of a new type of dry pellet, classified as "soft-dry pellet (SDP)" for yellowtail,1) has opened up the possibility of utilizing alternative protein sources as substitutes for fish meal in practical diets for ma rine finfish. Therefore, availability of various plant and animal protein ingredients as a protein source has already been tested using SDP in red sea bream and yellowtail.2-7) The results hitherto obtained have shown that defatted soy bean meal (SBM) can be included as a protein source up to 30% in place of fish meal without any adverse effects 2,3) and even up to 50% SBM without influencing palatability and acceptability.3) In addition, a diet with 25% SBM and 15% corn gluten meal (CGM) showed better feed perfor mance than the ...