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N-3 ESSENTIAL FATTY ACIDS IN NILE TILAIA, Oreochromis niloticus: THE EFFECTS OF DIETARY LINOLENIC ACID AND PROTEIN LEVELS ON GROWTH PERFORMANCE AND BODY COMPOSITION

Qing Pan*, Chen Cuiying, Wang Yadi, Li Xiaoxia
Department of Aquaculture, College of Animal Science, South China Agricultural University, Guangzhou 510642, China (qpan@scau.edu.cn)

The experiment was conducted to investigate the effects of dietary α-linolenic acid (LNA) and protein levels on growth performance and body composition in Nile tilapia, Oreochromis nilotica. Six isolipidic semi-purified experimental diets were formulated to contain two protein levels at 25% and 30%, each of which had three levels of LNA at 0% (control group), 0.5% and 1.5%, respectively. Diets were fed to juvenile fish with initial body weight of 1.7g in quadruplicate tanks in a recirculated -water system for 10 weeks. The results showed that compared to the control group, weight gain rate, specific growth rate, feed efficiency, protein efficiency rate and protein deposition rate increased significantly in fish fed diets with both 0.5% and 1.5% of LNA (P < 0.05), while no significant differences were observed between 0.5% group and 1.5% group (P > 0.05). Weight gain rate, specific growth rate and feed efficiency of 30% protein group were significantly higher than those of 25% protein group (P < 0.05), while protein efficiency rate and protein deposition rate showed the reverse patterns. Moreover, an interaction between dietary protein and α-linolenic acid on specific growth rate was abserved (P < 0.05). Fish fed diets with 0.5% and 1.5% of LNA showed significantly lower viscerosomatic index and intraperitoneal fat index than those of the control group (P < 0.5%), while no significant differences were observed in hepatosomatic index and condition factor among all the treatments (P > 0.05). Muscle lipid content significantly decreased with the increase of dietary LNA level (P < 0.5%), while muscle protein content showed a reverse pattern (P < 0.5%). Muscle protein content of 30% protein group was significantly higher than that of 25% protein group (P < 0.05). The results of the study indicated that dietary LNA could improve growth, feed and protein utilization and protein deposition in muscle as well as decrease lipid deposition in muscle and viscus. It suggested that there was a significant protein-sparing effect of dietaryα-linolenic acid in juvenile Nile tilapia.

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