Effects of dietary rapeseed meal levels on growth performance, biochemical indices and flesh quality of juvenile genetically improved farmed tilapia

An 8 week feeding study was conducted to investigate the effects of dietary rapeseed meal levels on growth, serum biochemical indices and flesh quality of juvenile genetically improved farmed tilapia, Oreochromis niloticus (GIFT) (initial body weight 26.81 g). Five isonitrogenous and isoenergetic diets (Diets RM1, RM2, RM3, RM4 and RM5) were formulated containing 0%, 11.6 %, 23.2 %, 34.8 % and 46.4 % of rapeseed meal, respectively. The values for weight gain, specific growth rates and feed efficiency of fish fed with RM4 and RM5 diets were significantly lower than those of fish fed with other diets. Fish fed with RM4 and RM5 diets had significantly lower serum alkaline phosphatase activity and total protein content than those fed with RM1 diet. The highest serum triglyceride concentration was observed in fish fed with RM5 diet. Dietary treatments had no significant influence on whole body and muscle moisture, crude protein, and ash contents. However, crude lipid content in the whole body and muscle of fish fed with RM4 and RM5 diets was significantly higher than that of fish fed with other diets. Lysine concentrations in the muscle decreased with increasing levels of RM. Similar trends were observed in hardness, cohesiveness, chewiness and springiness of fish. Broken-line analysis revealed that the appropriate dietary RM supplementation level of GIFT is 22.08 % based on weight gain.