Effects of dietary probiotic, Lactococcus lactis “subspecies PTCC 1403” on the growth parameters and survival rate of grey mullet (Mugil cephalus L.) against Lactococcus garvieae bacteria

The present study was conducted to investigate the effects of diet supplementation  with probiotic Lactococcus lactis “subspecies PTCC 1403” on the growth performance and survival rate of grey mullet (Mugil cephalus) for 30 days. The experiment was conducted in a completely randomized design with 450 grey mullet juveniles with average weight of 8.44±1.40g in 5 treatments and 3 replicates (n=30 in each replicate), consisting of two control treatments using non-supplemented food, and three experimental treatments (D1, D2 and D3) which were supplemented with this probiotic with concentrations of 1.5× 108, 3×108, 6×108  CFU /g feed respectively. After 30 days feeding with experimental diets, 10 fish per replication of experimental treatments and one control treatment were challenged by immersion method withlive pathogenic bacteria Lactococcus garvieae (1×107 CFUml-1) for 1 minute and their mortality were recorded for 10 days. The results showed that all of the measured growth parameters and survival rate in treatments containing  probiotic improved, but there were not significant differences compared to control group (P>0.05), and only the Condition Factor (CF) parameter in D2 and D3 treatments was significantly different with the control group (P<0.05). Survival percent increased to 64% in D3 and 68% in D2 compared with 40% in the control group (P <0.05). Overall we concluded that the using of this probiotic in the diet of grey mullet could increase survival rates against Lactococcus garvieae bacteria.