This study was carried out to evaluate the effect of replacing fish meal protein with fermented soybean meal (FSM) on growth performance, feed utilization, morphological parameters, amino acid profile, body composition, activity of antioxidant and digestive enzymes and blood chemistry in diet of juvenile olive flounder (Paralichthys olivaceus). Five isonitrogenic and isolipidic diets were prepared with using 0 (control), 80, 160, 240 and 320 g kg-1 FSM in diets. Juvenile olive flounder with initial average weight of 11.9 ± 0.19 g were randomly distributed in fifteen 300 L tanks. Triplicate groups (30 fish for each tank) of juvenile fed each diet to visual satiation at two meals per day for 8 weeks. The fish fed diets containing up to 240 g kg-1 FSM had no significant differences in the survival, growth, feed efficiency and protein efficiency ratio compared with control group. Fish fed diet containing 320 g kg-1 FSM had significantly lower survival, growth, feed efficiency and protein efficiency ratio compared with control group. Hepatosomatic index of fish fed diets containing 240 and 320 g kg-1 FSM was higher than control group. Triglyceride and total protein of plasma in fish fed the diets containing 80-320 g kg-1 FSM were higher than control group. Proximate composition of whole body, amino acid profile of dorsal muscle, activity of digestive enzymes in intestine and also the activity of antioxidant enzymes in fish liver and plasma were not affected by different levels of FSM compared with control group. This study showed that FSM has potential to replace fish meal up to 240 g kg-1 in diet of juvenile olive flounder.
