Submitted to: Journal of Applied Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2006
Publication Date: 6/20/2007
Citation: Aksoy, M., Lim, C.E., Davis, A.D., Shelby, R.A., Klesius, P.H. 2007. Influence of Dietary Lipid Sources on the Growth Performance, Immune Response and Resistance of Nile Tilapia, Oreochromis niloticus, to Streptoccus iniae Challenge. Journal of Applied Aquaculture. Vol. 19(2) 2007. pgs. 29-49. Interpretive Summary: There is evidence that dietary lipids influence the fatty acid composition, immune responses and disease resistance of fish. Early lipid requirement studies appear to indicate that both n-6 and n-3 series of fatty acids are dietary essential for tilapia. Previous research evaluating dietary lipid sources indicated that Nile tilapia fed diets supplemented with soybean oil or corn oil rich in n-6 grew better than those fed diets containing fish oil rich in n-3 highly unsaturated fatty acid and beef tallow rich in n-9. This study was conducted to evaluate the effect of dietary lipid sources, namely corn oil (CO), beef tallow (BT), menhaden fish oil (FO), linseed oil (LO), and equal combinations of FO+CO+BT or LO+CO+BT on growth performance, body fatty acid composition, hematology, immune responses and resistance of Nile tilapia to a gram positive bacteria called Streptococcus iniae infection. Diets were fed to juvenile Nile tilapia to apparent satiation (i.e., until fish no longer accept feed) twice daily for 12 weeks. Results showed that tilapia fed the beef tallow exhibited very poor performance. The sources of dietary lipid had no effect on hemoglobin and hematocrit. However, red blood cell and white blood cell counts were highest in fish fed the FO diet. Abnormally high red blood cell counts but similar hematocrit values in tilapia fed the FO diet as compared to those fed other diets indicate the presence of large numbers of small, immature red blood cells. Fatty acid composition of tilapia was affected by dietary lipid sources as has been reported for other fish species. Excessive levels of n-3 highly unsaturated fatty acid (FO diet) lead to abnormally high red and white blood cell counts and excessive mucus production. High levels of whole body n-9 to dietary n-9 (beef tallow) may be an indication of essential fatty acid deficiency in Nile tilapia and resulted in decreased immune response. The present study indicates that Nile tilapia have a dietary requirement for both n-6 and n-3 to maintain normal physiological and immunological functions.
Technical Abstract: This study was conducted to determine the effect of dietary lipid sources on growth performance, body fatty acid composition, hematology, immune response and resistance of Nile tilapia (Oreochromis niloticus) to Streptococcus iniae infection. Six isocaloric (13.4 MJ kg-1) and isonitrogenous (340 g kg-1 crude protein) semi-purified diets were supplemented with 70 g kg-1 of various sources of lipid, namely corn oil (CO), beef tallow (BT), menhaden fish oil (FO), linseed oil (LO), and equal combinations of FO+CO+BT or LO+CO+BT. Diets were fed to tilapia in quadruplicate aquaria to apparent satiation twice daily for 12 weeks. Fish fed the BT diet exhibited significantly lowest weight gain, feed intake, feed and protein efficiency ratios, apparent protein utilization and survival. Whole-body proximate composition was similar for all treatments except for fish fed the BT diet which had significantly lower crude protein and higher ash content. Whole-body fatty acid composition was a reflection of dietary fatty acid composition. Highest levels of total n-3 fatty acids (mostly 18:3 n-3) and total n-6 fatty acids (mostly 18:2n-6 and 20:3n-6) were recorded in fish fed LO and CO diets, respectively. Tilapia fed the FO diet contained highest levels of n-3 highly unsaturated fatty acids (n-3 HUFA) (20:5n-3 and 22:6n-3). Highest amounts of saturates (16:0 and 18:0) and monoenes (18:1n-7, 18:1n-9 and 20:1n-9) were deposited in fish fed the BT diet. No significant differences were found among hematological values of tilapia fed diets with different sources of lipid, except for fish fed the FO diet which had abnormally high red and white blood cell counts. Serum protein concentration, serum lysozyme activity and natural hemolytic complement activity were significantly lowest in fish fed the BT diet. The values of these parameters did not differ among fish fed other diets. Post-challenge antibody titers and the number of days at which the first mortality occurred were not influenced by dietary lipid sources. Cumulative mortality 14 days post-challenge with S. iniae was significantly lower for fish fed the BT diet compared to those fed FO or FO+CO+BT diets. No significant differences were observed in fish fed other dietary lipid sources.