Effects of dietary lipids and temperature on growth, liver fatty acid composition, and immune responses in channel catfish / Débora Machado Fracalossi.

Tese (Ph.D.) - Auburn University, 1993

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 compostion 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 mehaden oil, beef tallow, and corn oil at 28ºC and 17ºC. 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 17ºC compared to 28ºC (P0.10). The primary n-3 HUFA in liver phospholipids in fish fed menhaden oil or mixed oils was docosahexaenoic acid (DHA), while in fish fed linseed oil there was a small amount of eicosapentaenoic acid (EPA) but no DHA. Weight gain and liver phospholipid data suggest that channel catfish have limited ability to chain elongate dietary linolenic acid to n-3 HUFA in the liver. At the high temperature, fish survival after challenge with Edwardsiella icataluri was lower (P0.10) for fish fed linseed and menhaden oil diets. There was no difference in survival among treatments at the low temperature (P0.10). However, antibody production against E. ictaluri (measured only at 28º 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 (P0.10) 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 on 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.