SCREENING OF POLYHYDROXY BUTYRATE (PHB) ACCUMULATING BACTERIA FROM BIOFLOC SYSTEMS AND ITS EFFECT ON GROWTH, IMMUNOLOGICAL, ANTIOXIDANT INDICATORS AND DISEASE RESISTANCE OF GENETICALLY IMPROVED FARMED TILAPIA (GIFT)

PHB producing bacteria isolated from biofloc ponds were tested for its influence on GIFT Tilapia's growth, immune, antioxidant indicators and disease resistance was studied. Out of 40 bacterial isolates, 6 isolates namely  Bacillus infantis, Exiguobacterium profundum, Bacillus subtilis, Bacillus megaterium, Klebsiella pneumoniae and Enterococcus hirae showed positive results for PHB production against three fluorescent stains.  The PHB yield in the range of 0.21-4.2g/L was recorded based on the quantitative estimation of cell dry weight. Absorption band in the range of 4000Cm^-1 to 650Cm^-1 using FTIR analysis confirmed the C=O group in PHB produced by bacterial isolates. The highest recorded PHB from Klebsiella pneumoniae (T1) and Enterococcus hirae (T2) were further tested in the animals by supplementing PHB along with the feed (5g/kg) as treatments and without PHB as  control (C ) for 30 days. Significant difference (P< 0.05) in weight gain and specific growth rate were observed between treatments and control with 100% survival. Serum protein, Myeloperoxidase activity, RBT, Catalase, Glucose and SOD were significantly different between the treatments and control. Increased relative percent survival after 10 dpi of Aeromonas hydrophila was observed in T1 and T2. Overall improved immune response in GIFT tilapia fed with PHB extracted from biofloc systems exhibited biocontrol effect of PHB producing bacteria.