Probiotic bacteria as growth promoter and biocontrol agent against Aeromonas hydrophila in Catla catla (Hamilton, 1822)

Abstract

The current study reveals the antagonistic effect of Lactobacillus plantarum and Bacillus megaterium against Aeromonas hydrophila. Both probiotic bacteria (L. plantarum and B. megaterium) were added to commercial fish diet with 35% crude protein to evaluate their effect on the growth performance and survival rate, besides blood parameters like red blood cell (RBC) and white blood cell (WBC) counts in Catla catla. Two hundred and forty catla fingerlings with an average body weight of 6.10 g per fish were equally divided into four treatments of three replicates. T1 was given basal diet (control), T2 with L. plantarum (initial number of 107 cells g diet-1), T3 with B. megaterium (initial number of 107 cells g diet-1), and T4 was given basal diet with both L. plantarum and B. megaterium (mixed in 1:1 ratio). The experimental period was 60 days. Fish were challenged by A. hydrophila (3% of total body weight i.e., 107 ± 1 cells g – 1) via feed and observed for 15 days. The best growth rate, feed utilization and survival rate were noticed in T2 WBC and plasma protein level gradually decreased in T4, but RBC level increased in T4. The challenged fish of T4 showed 25% mortality, while T1, T2 and T3 showed 80%, 35% and 50% mortality respectively. Combination of two probiotics (L. plantarum and B. megaterium) has significantly enhanced fish growth and health indicating the potential use of a combination of L. plantarum and B. megaterium as feed probiotic in aquaculture.