Protected forms of sodium butyrate improve the growth and health of Nile tilapia fingerlings during sexual reversion

The present study evaluated the effect of pure and protected sodium butyrate with palm oil and buffered solution supplemented in the diet of Nile tilapia Oreochromis niloticus on the performance parameters, hematological parameters and disease resistance during sexual reversion. Initially, the minimum inhibitory concentration (MIC) of sodium butyrate (Na-butyrate) against Aeromonas hydrophila or Streptococcus agalactiae under three different pH to determine the concentration of inclusion of Na-butyrate in the diet were analyzed. After that a total of 3150 newly hatched post-larvae were distributed in 21 tanks with 100 L of capacity on six treatments and one control, in triplicate: fish fed unsupplemented diet (control); fish fed Na-butyrate supplemented diet (Pure 0.25% and Pure 0.5%); fish fed Na-butyrate coated with palm oil (Oil 0.25% and Oil 0.5%) and fish fed Na-butyrate coated with buffered solution (Buffer 0.25% and Buffer 0.5%). After 28 days of feeding, zootechnical parameters, hematological parameters and resistance against A. hydrophila were verified. The MIC results showed that Na-butyrate had a better inhibitory effect in vitro at pH 6 and 6.6 than at pH 7, regardless of the microorganism. The addition of Na-butyrate at different concentrations and forms did not influence the sexual reversal process of tilapia. Yield and biomass gain showed an increment in fish fed Buffer 0.5% and Oil 0.5%. Moreover, fish fed Oil 0.5% had a better feed conversion ratio than the other groups. An increase in the red blood cells (RBC) and monocytes were observed in fish fed Buffer 0.5% and Oil 0.25% when compared to control group, while those fed Pure 0.25% and Oil 0.5% showed the lowest monocytes number when compared to Buffer0.5% and Oil0.25%. After challenge by immersion in A. hydrophila solution, no difference was found among the treatments for 14 days of observation, except for the nonchallenged fish that showed no mortality ensuring the effectiveness of the experimental infection. The use of coated Na-butyrate either in buffer or oil showed to be feasible to improve the zootechnical parameters of Nile tilapia during the sexual reversion period.