Effects of dietary lipids and temperature on growth, liver fatty acid composition, and immune responses in channel catfish

A series of feeding experiments were conducted with young channel catfish in aquaria to evaluate the effects of various dietary lipids and temperatures on growth, liver fatty acid composition and response to challenge with Edwardsiella ictaluri. Fish were fed semipurified diets containing 7% lipid as beef tallow, corn oil, linseed oil, menhaden oil or a mixture (1:1:1) of menhaden oil, beef tallow, and corn oil at 28{dollar}spcirc{dollar}C and 17{dollar}spcirc{dollar}C. At both temperatures, fish fed menhaden oil and mixed oil diets exhibited the highest weight gains, while fish fed beef tallow had the lowest weight gain. Both diets were rich in n-3 highly unsaturated fatty acids (HUFA), suggesting a requirement for n-3 HUFA in promoting growth. The concentration of polyene fatty acids in liver phospholipids was higher in fish grown at 17{dollar}spcirc{dollar}C compared to 28{dollar}spcirc{dollar}C (P {dollar}{dollar} 0.10). However, antibody production against E. ictaluri (measured only at 28{dollar}spcirc{dollar}C) was higher in fish fed menhaden oil than in the other fish. Leukotriene B production in anterior kidneys was highest in fish fed corn oil at the high temperature (P {dollar}<{dollar} 0.10) but not at the low temperature. Fish fed beef tallow produced the lowest amount of leukotriene B at both temperatures. The lower resistance to E. ictaluri infection by channel catfish fed the linseed oil and menhaden oil diets suggests that diets with a high concentration of n-3 fatty acids or a high ratio of n-3 to n-6 fatty acids may suppress the synthesis of immunostimulatory eicosanoids in channel catfish at warm temperatures.