ARS | Publication request: Growth, body fatty acid composition, immune response and resistance to Streptococcus iniae of hybrid tilapia, Oreochromis niloticus X O. aureus, fed diets containing various levels of linoleic and linolenic acids

Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 2, 2012
Publication Date: N/A

Interpretive Summary: Published information indicates that tilapia have a dietary requirement for linoleic (n-6) series fatty acids. The optimum dietary levels of these fatty acids reported were 0.5 and 1% for redbelly tilapia and Nile tilapia, respectively. It has been suggested that tilapia also have a requirement for linolenic (n-3) series of fatty acids, but the optimum dietary requirement levels of n-3 for various tilapia species are unknown. Studies evaluating various lipid sources, however, have shown that plant oils rich in n-6 and/or n-3 fatty acids, such as soybean oil, corn oil, sunflower oil, canola oil, palm oil products and linseed oil were suitable lipid sources for tilapia. Thus, this study was conducted to evaluate the effects of various levels of dietary linoleic (LA), linolenic acids (LN) or their combination on growth, body fatty acid composition, hematology, immune response and disease resistance of juvenile, sex-reversed all-male hybrid tilapia. A basal purified diet (34% crude protein and 3.2 kcal DE/g) supplemented with 6% coconut oil (diet 1, 0.12% LA and 0% LN) and nine test diets containing 0.5, 1.0 and 2% of LA (diets 2-4), 0.5, 1.0 and 2% of LN (diets 5-7), and a combination LA and LN, each at levels of 0.25, 0.50 and 1.00% (diets 8-10) were formulated. Since flaxseed oil that was used as the source of LN also contains LA, diets 5, 6 and 7 contain, in addition to LN, 0.26, 0.40 and 0.69% LA, respectively. Each diet was fed to tilapia in triplicate tanks twice daily to apparent satiation for 10 weeks. Fish fed the control diet (diet 1) lacking of both LA and LN had the lowest weight gain (WG). Fish fed diet 3 (1.0% LA) had the highest WG, but no differences were found when compared with those fed diets 2, 4-5 and 7-10. Feed consumption, feed efficiency ratio and survival were similar for among fish in all treatments. Fatty acid (FA) composition of fish is generally a reflection of dietary FA. Whole body total n-6 increased with increasing dietary levels of n-6. There was also a trend of increasing body n-3 content with increasing dietary levels of n-3, but the values peaked at a dietary concentration of about 1%. Tilapia accumulated higher levels of n-6 than n-3 as the body ratios of n-6 to n-3 greatly increased relative to dietary ratios, especially in fish fed diets 5-10. Dietary treatments had no effect on hematological and immunological parameters and the resistance of fish to bacterial (Streptococcus iniae) infection. This study indicates that both LA and LN are essential for growth of juvenile O. niloticus x O. aureus hybrid. However, compared to LN, LA appears to have a better growth promoting effect. Dietary LA alone can meet the EFA requirement of O. niloticus x O. aureus hybrid, and a level of 1.14% of diet is required for optimum growth.

Technical Abstract: The effects of dietary linoleic (LA) and linolenic acids (LN) on growth and immunity of all-male hybrid tilapia, Oreochromis niloticus × O. aureus, were evaluated for 10 weeks. Fish fed 0.12% LA + 0% LN had the lowest weight gain (WG) but was not significantly different from diets containing 0.5% LA or 0.40% LA + 1.0% LN. Fish fed 1% LA had the highest WG but did not differ from diets with 0.5% LA, 2.0% LA, 0.26% LA + 0.5% LN, 0.69% LA + 2.0% LN, or diets containing both LA and LN at 0.25, 0.5, and 1.0%. Feed intake, feed efficiency, and survival did not differ among treatments. Total body n-6 FAs increased with increasing dietary levels of n-6. Total body n-3 FAs also appeared to increase with increasing dietary n-3 levels but peaked at 1% of diet. Dietary treatment had no effect on hematology, immune function, or survival to Streptococcus iniae. This study indicates that both LA and LN are dietary essential for growth of hybrid tilapia, but LA appears to have better growth promoting effect than LN. Dietary LA alone can meet the EFA requirement, and a level of 1.14% of diet is required for optimum growth.