Submitted to: Aquaculture Conference Proceedings
Publication Type: Abstract only
Publication Acceptance Date: 12/1/2006
Publication Date: 2/26/2007
Citation: Aksoy, M., Lim, C.E., Shelby, Richard A., Klesius, P.H. 2007. Increasing Fish Oil Levels in Commercial Diets Influence Hematology and Immune Responses of Channel Catfish, Ictalurus punctatus. Aquaculture Conference Proceedings. Aquaculture 2007. February 26 - March 2, 2007 San Antonio , Texas. p. 1024. Interpretive Summary:
Technical Abstract: Cultured freshwater fish including channel catfish are commonly fed grain-soybean meal based feeds high in linoleic series (n-6) fatty acids. Published studies have shown that supplementation of catfish diets with marine fish oil rich in n-3 highly unsaturated fatty acids (n-3 HUFA) significantly influenced fatty acid composition, immune parameters and susceptibility to infectious pathogens. These fatty acids (n-3 HUFA) are readily incorporated into polar lipids in cellular membranes. Their presence in the cell membrane affects the functions of immune cells. Suboptimal and/or excess of any essential dietary nutrients, including n-3 HUFA, however, may adversely affect immune response and disease resistance of fish. Growth performance, immune responses and disease resistance were studied in channel catfish, Ictalurus punctatus fed a commercial diet containing 5.6% lipid supplemented with menhaden fish oil at levels of 0, 3, 6, and 9%. Each diet was fed to juvenile catfish in quadruplicate aquaria to satiation twice daily for 15 weeks. Levels of dietary fish oil did not significantly influence final weight gain, feed intake, feed efficiency ratio and survival of channel catfish. Fatty acid compositions of whole-body and liver were reflection of dietary fatty acid composition. Progressive increase in saturated and total n-3 fatty acids, and decrease in monoenoic and total n-6 fatty acids were observed as supplemental levels of fish oil increased. No significant differences were found among hematological values, except for fish fed the 9% added fish oil diet which had significantly lower hemotocrit. Susceptibility of erythrocytes to hemolysis in hypotonic solutions decreased progressively with increasing fish oil supplementation and erythrocytes of fish fed the highest fish oil diet were the most resistant. Fish fed diets with added fish oil at levels of 6% and 9% had significantly higher serum protein levels than that of the control. Increasing supplemented fish oil to 9% did not significantly stimulate lysozyme activity over the control. Serum natural hemolytic complement activity and macrophage chemotaxis ratio significantly decreased in fish fed diets supplemented with 6 and 9% fish oil. However, significantly highest natural complement activity was obtained in the group fed the diet with 3% added fish oil. Antibody production against Edwardsiella ictaluri 15-day post-infection was not signifcantly affected by levels of dietary fish oil. Likewise, dietary fish oil levels had no significant influence on cumulative mortality of channel catfish at 14-day post challenge with E. ictaluri.