Influence of dietary lipid sources on the growth performance, immune response, and resistance of Nile tilapia, Oreochromis niloticus, to Streptococcus iniae challenge.

摘要

Effects of various dietary lipid sources were investigated upon the growth performance, body proximate composition, haematology, immune response and resistance of Nile tilapia (Oreochromis niloticus) to Streptococcus iniae infection. 6 isocaloric (3.2 kcal/g) and isonitrogenous (34% crude protein) semi-purified diets were supplemented with 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, at a level of 7%. Diets were fed to tilapia in quadruplicate aquaria to apparent satiation, twice daily for 12 wk. Fish fed the BT-diet exhibited the lowest weight gain, diet intake, feed and protein efficiency ratios, apparent protein utilization and survival. Whole-body protein and ash were lowest and highest, respectively, for fish fed the beef tallow-diet (P < 0.05), but the values of these parameters did not differ among fish fed the other diets. No significant differences (P > 0.05) were found among haematological values, except for fish fed the FO-diet which had abnormally high red and white blood cell counts. Serum protein concn., lysozyme activity and natural haemolytic complement activity were significantly (P < 0.05) reduced in fish fed the BT-diet. The values of these parameters did not differ among fish fed other diets. Post-challenge antibody titer was not influenced by dietary lipid source. Cumulative mortality 15 days post-challenge with S. iniae was significantly lower (P < 0.05) for fish fed the BT diet compared with those fed FO or FO+CO+BT diets. No significant differences were observed in fish fed other dietary lipid sources.