Pathological evaluation to the effect of some probiotics on the health and immune status of Nile Tilapia (Oreochromis niloticus) By

T he safety and efficiency of Bacillus subtilis and/or Lactobacillus acidophilus, as potential probiotics, were evaluated histopathologically and immnunologically besides after challenge infection through an experiment using 960 Nile tilapia (Oreochromis niloticus) reared in aquaria. The experimented fish divided into 4 equal groups. Groups 1- 3 fed daily on a basal diet supplemented with probiotics, the 4th group served as a control and fed on basal diet only. All fish fed at a rate of 5% of the body weight for 1 and 2 months. The feed conversion and specific growth rates showed no significant change after one month of application but a significant to non-significant increase were remarkable after 2 months of treatment. The survival rate was significantly increased in the fish given B. subtilis and L. acidophilus for one and two months after application. The histopathological studies revealed minimal pathological alterations, in the examined organs of Nile tilapia from different supplemented groups, but an obvious activation in the hematopoietic tissues and melanomacrophage centers were recognized. The serum bactericidal activity and the mortality after the challenge infections were varied with the type of probiotic bacteria used, type of pathogen tested and period of application but as a general observation, it was high in the group that given a mixture of B. subtilis and L. acidophilus and groups treated for 2 months. Based on the following observations where, the tested bacteria proved to have a potential probiotic effect, enhancing the immunity and health status of the experimental fish. Such probiotics promoted the resistance against the bacterial infections. No remarkable pathological alterations were recognized in groups treated with single or mixed probiotic candidate. It could be concluded that, one month application was sufficient and a mixture of the two probiotics was superior. However, full commercial cost benefit analysis is recommended. KEY WORDS: Probiotics, Bacillus subtilis, Lactobacillus acidophilus, histopathology, bactericidal activity, Aeromonas hydrophila, Pseudomonas fluorescens, Streptococcus iniae, Oreochromis niloticus.