Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2009
Publication Date: 12/1/2009
Citation: Lim, C.E., Aksoy, M., Li, M.H., Welker, T.L., Klesius, P.H. 2009. Influence of dietary levels of lipid and vitamin E on growth and resistance of Nile tilapia to Streptococcus iniae challenge. Aquaculture. 298: 76-82.
Interpretive Summary: Dietary lipids (fats/oils) are an important source of highly digestible energy and are the only source of essential fatty acids required by fish for normal growth, development and maintaining health. Tilapia also have a dietary requirement for vitamin E and the requirement levels increase with increasing levels of dietary lipid. Deficiency or excess dietary lipid and/or vitamin E have been reported to reduce immune responses and decrease the resistance to infectious disease in several fish species. Thus, this study was conducted to evaluate the effect of dietary lipid levels on vitamin E requirement and their interaction on growth performance, immune responses and resistance of Nile tilapia to Streptoccocus iniae challenge. Data of the current study show that, based on weight gain, feed intake, feed efficiency ratio and survival, vitamin E requirement of Nile tilapia was not affected by dietary oil levels and supplementation of 50 mg of vitamin E/kg of practical diet (analyzed average value of 112 mg/kg) was sufficient for Nile tilapia fed diets containing an equal mixture of corn oil and menhaden fish oil ranging from 6 to 14%. However, regardless of the dietary levels of vitamin E, increasing the level of supplemental lipid to 14% resulted in decreased feed efficiency and accumulation of body lipid. Liver content of vitamin E increased with increasing dietary level of vitamin E, decreased with increasing dietary levels of lipid and became significantly lower at 14% supplemental lipid. Hematological values and HSI were unaffected by dietary levels of lipid or vitamin E. Dietary lipid levels had no effect on serum lysozyme but an increase in serum protein and decrease in serum alternative complement activity were observed at 14% and 10 or 14% dietary lipid, respectively. Increasing supplemental levels of vitamin E to 100 or 200 mg/kg diet positively affected serum lysozyme and complement activity but had no influence on serum protein. Even though some immune parameters were affected by dietary levels of lipid and vitamin E, at levels used, these dietary nutrients appear to be of no benefit in increasing resistance of Nile tilapia to S. iniae. Based on this information, it is recommended that the total dietary fat in diets of juvenile tilapia diets should not exceed 10% and vitamin E supplementation of 50 mg/kg diet was sufficient for normal growth performance and health.
Technical Abstract: A study was conducted to determine the effect of dietary levels of lipid and vitamin E on growth performance, immune responses and resistance of Nile tilapia to Streptococcus iniae challenge. A basal purified diet (35% protein and 3.4 kcal DE/g) supplemented with 6, 10 and 14% of 1:1 mixture of corn oil and menhaden fish oil were each supplemented with 50, 100 and 200 mg vitamin E/kg. Each diet was fed to Nile tilapia in triplicate aquaria for 12 weeks. Weight gain, feed intake and survival were not affected by dietary levels of either lipid or vitamin E. Feed efficiency in fish fed 14% lipid diets was significantly lower than that fed 6% dietary lipid but these did not differ from that of the 10% dietary lipid diet. These variables were not affected by dietary vitamin E levels. Whole body lipid significantly increased in fish fed 14% lipid diets and 100 mg/kg vitamin E diets. Liver vitamin E levels were reflection of dietary levels of vitamin E. Increasing dietary levels of lipid to 14%, however, significantly decreased liver concentration of vitamin E. Hematological parameters and hepatosomatic indices were not affected by dietary treatments. Serum protein significantly increased in fish fed 14% lipid diets but was not affected by supplemental levels of vitamin E. Lysozyme activity was not affected by dietary lipid levels but significantly increased in fish fed 200 mg vitamin E diets. Alternative complement activity significantly decreased in fish fed 10 or 14% dietary lipids but increased when dietary vitamin E levels was increased to 100 or 200 mg. Dietary lipid and vitamin E levels had no effect on the resistance of Nile tilapia to S. iniae infection and or antibody titer against that bacterium.