Different via to apply the Gamaxine® commercial biopromoter to Nile tilapia evaluating the immune system responses to Streptococcus agalactiae Ib

Abstract

This study evaluated the use of biopromoter Gamaxine for fish, a product elaborated from the fermentation of purified cultures of inactivated saprophytic bacteria, at the original concentration of 1.0 g L−1, to favor the equilibrium of the intestinal microbiota, providing better protection against the enteric challenges. It is used originally as against enteric challenges and consequently improving the productive performance of poultry. The biopromoter was manufactured by Vetanco company for evaluation under experimental conditions to be tested and validated as an immunomodulator in the Nile tilapia Oreochromis niloticus, against the pathogen Streptococcus agalactiae serotype Ib by different routes of application: oral, immersion and intraperitoneal, as compared to a naïve group and a control group immunized with commercial vaccine. A total of 315 Nile tilapia's juveniles with initial mean weight of 0.72 ± 0.04 g. The treatments were randomly distributed in triplicates in 21 experimental units in a water recirculation system. Different doses of the biopromoter were fractionated for each route of application. In the oral route, 0.1 mg and 0.2 mg of the biopromoter were added to each gram of feed offered; for the immersion bath 500 mg and 1000 mg of the biopromoter diluted in 4.5 L and 4.0 L respectively were used; and for intraperitoneal injection, 0.2 mg per fish. After 54 days of the experiment, the samples were collected for hematological, immunological, histological and enzymatic analyzes. At day 55 the fish were challenged with S. agalactiae, to verify the efficacy of the biopromoter and the possible increase of the bacterial resistance to the pathogens, as well as physiological changes in the fish. Hematoimmunological, histological and enzymatic pre-infection analyzes revealed that the treated fish presented improvements in the immune system, indicating that these animals were better prepared to confront the bacteria. After the experimental infection the fish in the treated groups increased the resistance the pathogen. All the results of this study indicate that the tilapias that received the biopromoter developed improvements in the mechanisms of the immune system and the zootechnical performance.