Influence of dietary lipid and temperature on bactericidal activity of channel catfish macrophages

We fed juvenile channel catfish Ictalurus punctatus purified diets containing different lipid sources for 90-110 d to examine the influence of dietary lipids on intracellular killing of Edwardsiella ictaluri by pronephros macrophages. The diets contained either menhaden oil, soybean oil, beef tallow, or a combination of all three lipids. We performed the study with nonimmune and immunized fish acclimated to optimal (28°C) and suboptimal (19°c) temperatures. In both temperature trials, bactericidal activity was positively correlated with the level of n-3 fatty acids in the diet (particularly long-chain highly unsaturated fatty acids). Vaccination resulted in substantially enhanced bactericidal activity, except at suboptimal temperature in fish fed the diet containing beef tallow (primarily saturated and monoenoic fatty acids). Overall results were similar at optimal and suboptimal temperatures. This study demonstrates the potential for nutritional manipulation of disease resistance in fish and illustrates the need for standardized diets in fish health research.