Effect of feed type and feeding frequency on macrophage functions in tilapia (Oreochromis niloticus L.)

In fresh water recirculation systems the type of feed and feeding frequency have a direct effect on water quality, growth, fish welfare and the response of the immune system. Four types of feed with different sources of plant protein (soybean concentrate, sunflower meal, corn gluten and pea) were provided at two feeding frequencies (two and eight times day(-1)) to observe effects on growth, cortisol levels and innate immunity (macrophage phagocytosis and respiratory burst) on tilapia in early stages of growth (2-10 g). Growth and cortisol parameters were quite similar among the groups of tilapia fed the different diets and frequencies at the end of the feeding period. Phagocytosis and respiratory burst were also very similar with the four feed types. However, macrophages from fish fed twice day(-1) were much less efficient in clearing bacteria after 24 h than the groups fed eight times day(-1). Our results suggest that an increased feeding frequency may confer a higher resistance to disease.