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¹ Olusegun Agagu University of Science and Technology, School of Agriculture, Food and Natural Resources, Department of Fisheries and Aquaculture Technology, Okitipupa/Ondo State, Nigeria DOI : 10.4194/AQUAST808 Viewed : 1416 - Downloaded : 788 This study evaluated the heterotrophic bacteria and fungi loads and water quality parameters when Lactobacillus plantarum was employed as bio-control agent during egg incubation of Clarias gariepinus. The L. plantarum cells were inoculated into incubating water in 6-litre bowl at bacterial concentration of 2×103, 2×106 and 2×109 cfu L-1. Bowls with 1 ppt tetracycline solution and with no test bacteria / drug served as positive and negative controls respectively. 3 g of C. gariepinus fertilized eggs were incubated in these bowls under static water condition for 30 hours at room temperature, after which hatchability was determined. The water in each bowl was analyzed before, during and after egg incubation. The results indicated that all L. plantarum treatment groups recorded significantly (p<0.05) reduced Enterobacteriaceae and fungi counts in the incubating water, with the optimum concentration recorded at 2×106 cfu L-1. There were significant reductions (p<0.05) in the dissolved oxygen and pH of water at 30 hours of incubation when compared with the values obtained at 10 hour of incubation in all experimental groups. The fertilized eggs hatched in all treatment groups except those inoculated with 2×10⁹ cfu L^-1 L. plantarum, while hatchlings from positive control (tetracycline solution) groups were observed to be less viable than the probiotic-treatment and negative control (non-probiotic treatment) groups. It can be concluded from this study that addition of 2×10⁶ cfu L^-1 of L plantarum into incubating water reduced microbial loads, but did not improve water quality parameters (dissolved oxygen and pH) and hatchability of C. gariepinus eggs. Keywords : Probiotics Hatchlings Inoculated Fungi