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N-3 essential fatty acids in Nile tilapia, Oreochromis niloticus: Quantification of optimum requirement of dietary linolenic acid in juvenile fish

Chen, Cuiying, Sun, Baoli, Li, Xiaoxia, Li, Peiyu, Guan, Wutai, Bi, Yingzuo, Pan, Qing
Aquaculture 2013 v.416-417 pp. 99-104
Oreochromis niloticus, acclimation, experimental diets, fatty acid composition, feed conversion, fish, freshwater, juveniles, linolenic acid, oleic acid, protein deposition, rearing, regression analysis, specific growth rate, weight gain
To quantify the optimum requirement of dietary linolenic acid (18:3n-3, LNA) for Nile tilapia (Oreochromis niloticus), purified ethyl linolenate was added to the basal diet to provide the dietary LNA level of 0.00, 0.10, 0.32, 0.63, 0.98, 1.56 and 2.04% of dry weight, respectively. All diets contained similar amounts of 18:2n-6 (0.61% of dry weight) and 18:1n-9 from purified ethyl linoleate and oleate, respectively. Basal diet without LNA was considered as a control. After 2-week acclimation with a lipid-free diet, 4 replicate groups of 120 juvenile fish with initial body weight of 2.10g were fed with experimental diets in a recirculated fresh water rearing system for 10weeks. Feeding rate was 10% of body weight in the first 2weeks, 8% in the following 4weeks, and then gradually reduced to 5% in the next 4weeks. Fish were fed three times daily at 8:30, 12:00 and 17:00. The results showed that fish fed the diet with 0.63% of LNA had significantly higher weight gain (WG) and specific growth rate (SGR) than fish fed the control diet (P<0.05). Feed efficiency (FE) and protein deposition (PD) in fish fed diets with 0.63, 0.98, 1.56 and 2.04% of LNA were significantly higher than those of the control group (P<0.05). Fish muscle fatty acid composition reflected dietary fatty acids. Increasing dietary LNA levels resulted in increased contents of LNA and 22:6n-3, but decreased contents of 20:4n-6 and 20:5n-3. When WG and FE were subjected to broken-line regression analysis, the breakpoint was achieved at dietary LNA levels of 0.45 and 0.64% of dry weight, respectively. Based on those results, the recommended optimum requirement of dietary LNA for juvenile tilapia is 0.45–0.64% of dry weight.