Inclusion of yeast and/or fructooligosaccharides in diets with plant-origin protein concentrates for rainbow trout (Oncorhynchus mykiss) fingerlings

Prebiotics and probiotics improve growth and immune responses in fish. However, their inclusion affects fish when combined with plant proteins is not well studied. The effects of diets with plant concentrates supplemented with yeast Saccharomyces sp. (Y) and/or fructooligosaccharides (FOS) on growth and nonspecific immune responses were determined in rainbow trout. A basal diet (soy, rice protein concentrates, and corn gluten-200, 200, and150 g/kg, respectively) was supplemented with Y (15 g/kg), FOS (5 g/kg), or Y + FOS (15 and 5 g/kg). The basal diet corresponded to the control. Triplicate tanks with 20 fingerlings (initial weight of 1.3 +/- 0.1 g; mean +/- SE) were fed for 70 days. Higher values of weight gain and specific growth rate were observed in fingerlings fed with Diet Y; the lowest values were observed in the control group. Leucocytes were higher in fish fed with the FOS diet, whereas the burst activity of macrophages was higher in Y-fed fish. Lysozyme activity in the serum did not show differences among the experimental groups, but significantly higher values were observed in the skin mucus of fish fed Diet Y. The present research shows that the inclusion of yeast with plant protein concentrates improved the growth and burst activity of macrophages in the fingerlings.