Growth, Body Fatty Acid Composition, Immune Response, and Resistance to Streptococcus iniae of Hybrid Tilapia, Oreochromis niloticusOreochromis aureus, Fed Diets Containing Various Levels of Linoleic and Linolenic Acids

The effects of dietary linoleic (LA) and linolenic acids (LN) on growth and immunity of allmale hybrid tilapia, Oreochromis niloticus×Oreochromis aureus , were evaluated for 10 wk. 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 fatty acids (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. Dietary LA alone can meet the essential FA requirement, and a level of 1.14% of diet is required for optimum growth. Dietary lipids are important sources of highly digestible energy and are the only source of essential fatty acids (EFAs) required for normal growth and development for aquatic animals, including tilapia. They are also carriers and can assist in the absorption of fat-soluble nutrients, such as sterols and fat-soluble vitamins, serve as a source of phospholipids, and participate in the synthesis of hormones, prostaglandins, and other metabolically active compounds (Lim and Webster 2006; Lim et al. 2008). A number of studies have shown that the growth performance and health of fish, including tilapia, are affected by sources and levels of dietary lipids (Lim et al. 2011). 1 Corresponding author. Tilapias are the most widely and successfully cultured species worldwide due to a variety of desirable characteristics. But like other fishes and vertebrates, tilapia cannot synthesize the 18-carbon polyunsaturated FAs (Henderson and Tocher 1987) and have been shown to require a dietary source of linoleic (n-6) series FAs (18:2n-6 and 20:4n-6) for normal growth (Kanazawa et al. 1980b; Takeuchi et al. 1983) and reproduction (Santiago and Reyes 1993). The optimum dietary requirements of n-6 FAs for tilapias have been estimated to be 1.0% for redbelly tilapia, Tilapia zillii (Kanazawa et al. 1980b) and 0.5% for Nile tilapia, Oreochromis niloticus (Takeuchi et al. 1983). Likewise, linolenic (n-3) series FAs (18:3n-3, 20:5n-3, and 22:6n-3) have also been Published 2013. This article is a U.S. Government work and is in the public domain in the USA.