Impact of orange (Citrus sinensis) peel meal as feed additive in the diets for mono-sex Nile tilapia (Oreochromis niloticus) fries

: This experiment was conducted to evaluate the effect of orange peel meal as feed additive in the diets for mono-sex Nile tilapia fries on growth performance, body composition, carotenoids and the histology of liver and intestine. Two hundred and twenty-five fries at average weight of 0.52 ± 0.01 g/fry were randomly distributed in 15 hapa (1 m × 1 m × 0.5 m) placed in 5 concrete tanks measured (2 m × 2 m × 1 m) in three replicates for each treatment. Fish from each hapa were counted and weighed each two weeks to evaluate the growth and readjust the feeding rate. 10% of fish body weight were fed to every three groups of the experimental fish with one of the experimental diets and decreased gradually to 8 and 6% by the end of the feeding trial. The experimental diets were formulated to be similar in crude protein (33.6 ± 0.1%) and crude lipids (7.1 ± 0.1%). The formulated diets were performed (g/kg diet) as, 0 (CTRL), 10 (OP 10 ), 30 (OP 30 ), 50 (OP 50 ) and 70 (OP 70 ) orange peel meal. Fish were fed the experimental diets for 6 days per week, three times per day (9.00 a.m., 11 a. m. and 1 p.m.) for 98 days. There were no significant differences ( P>0.05 ) among all treatments in final body weight, gain and average daily gain except fish fed OP 10 diet were significantly differed and gained the highest values. In addition, no significant differences were observed in specific growth rate (SGR) among all treatments and the highest value was found in fish fed OP 30 diet. However, there were significant differences ( P<0.05 ) among all treatments in feed consumption and fish fed OP 10 diet consumed more feed than other groups and was significantly higher. The best FCR was obtained in fish fed OP 70 and OP 30 diets, respectively. Slight increase in PER was observed in fish fed OP 70 followed by fish fed OP 30 diets. No significant differences ( P > 0.05 ) were found in the survival rate among all treatments. Fish fed OP 70 and OP 50 diets gained the highest protein content and significantly differed among other treatments. Ether extract content of fish fed CTRL, OP 50 and OP 30 diets were the highest, and significantly differed with the other treatments. Also, the carotenoids content significantly differed ( P<0.05 ) among all treatments and the highest value was found in fish fed OP 70 diet. It was increased by increasing the level of orange peel meal in the diets. However, no abnormalities were observed in the examined liver and intestine related to the addition of orange peel meal at different levels in the experimental diets. It can be concluded that orange peel meal could be added to diets for mono-sex Nile tilapia at 10 g/kg diet without any adverse effects.