Immunostimulation by poly-β hydroxybutyrate–hydroxyvalerate (PHB–HV) from Bacillus thuringiensis in Oreochromis mossambicus

•First study to try poly-β hydroxybutyrate (PHB) as immunostimulant.•All the doses (1%, 3% and 5% (w/w)) of PHB–HV was effective.•PHB–HV has the potential to be used as an immunostimulant.

The present study was designed to test the immunostimulatory efficacy of poly-β hydroxybutyrate–hydroxyvalerate (PHB–HV) extracted from Bacillus thuringiensis B.t.A102 on the immune system of Oreochromis mossambicus. Fish were fed with 0%, 1%, 3% or 5% PHB–HV supplemented feed and were bled at regular intervals of 5 days. The specific immune response was measured in terms of antibody response to sheep red blood cells, the nonspecific immune mechanisms were analysed in terms of serum lysozyme activity, total peroxidases activity and antiprotease activity. The overall functional immunity was tested by experimental challenge with live virulent Aeromonas hydrophila. The results revealed that all the doses of PHB–HV supplementation in feed were effective in stimulating both specific and nonspecific immune mechanisms. The bacterial challenge experiment showed that highest dose of 5% PHB–HV supplementation was more effective than 1% and 3% doses. The study concludes that PHB–HV can be used as a potential immunostimulant in finfish aquaculture.