Dietary supplementation of Probiotic Enterococcus faecium improve resistance in Arapaima gigas against Aeromonas hydrophila

This study evaluated the mortality rate, histopathology and haematological parameters of Arapaima gigas against Aeromonas hydrophila after 68 days of dietary probiotic supplementation with autochthonous bacterium Enterococcus faecium. Three experiments were carried out: the first assay evaluated the lethality of A. hydrophila, the second and the third assay evaluated the fish supplemented subjected to A. hydrophila lethal dose 30% (106 CFU ml−1) and lethal dose 100% (108CFU ml−1) respectively. The clinical signs, blood changes, histopathological alterations and mortalities were evaluated. At the first experiment, the concentrations of 106 and 108CFU.mL−1 with A. hydrophila caused 33% and 100% of mortality. The A. hydrophila infection provoked clinical signs such as dark skin, ulceration, haemorrhage, pale gills and liver, hepatic alterations, hyperaemia, hepatic cord breakdown, cellular deforming, lipid degeneration and necrosis. In the second experiment, no mortality occurred onto fish fed with probiotic. Furthermore, in the third experiment, fish submitted to probiotic supplementation showed reduction in mortality of 75% compared with the control and fish fed with probiotic diets at 108CFU g−1 not presented any clinical signs. For these reasons, Arapaima gigas juveniles previously submitted to probiotic supplementation with E. faecium (108CFU g−1) shows better physiological and immunological response, improving resistance against A. hydrophila infection.