Effect of organic acids on water microflora used for larval rearing of fishes

Abstract

Ban on antibiotics usage due to residue problem and development of resistance forces the aquaculturists to find alternative strategies for controlling bacterial infections. In this context, organic acids can be used as one of the alternative for controlling bacteria mainly the pathogenic Vibrio spp. The present study reports the assessment of efficacy of different concentration of organic acids viz., 1, 0.2, 0.1, 0.075, 0.05, 0.025 on total aerobic bacterial count and presumptive vibrio count from water samples collected from milk fish larval rearing tank, at different time intervals. The study was conducted separately for all organic acids at six concentrations. Complete inhibition of bacterial flora was observed up to 0.1 per cent for all organic acids at all different time intervals but for all acids of concentrations The study was conducted separately for all organic acids at six concentrations. Complete inhibition of bacterial flora was observed up to 0.1 per cent for all organic acids at all different time intervals but for all acids of concentrations below 0.1 per cent, TPC and PVC at different time intervals ranged from 3.19 to 5.75 log cfu per millilitre and from 2.22 to 3.58 log cfu per millilitre, respectively. In contrast, TPC and PVC ranged from 6.37 to 6.90 log cfu per millilitre and 4.35 to 4.74 log cfu per millilitre for the untreated water samples. Organic acid treated water samples showed a significant decline in both the TPC and PVC for the concentrations 0.075, 0.05 and 0.025 of all acids compared to control. From the study, it was concluded that the effective concentration of organic acids should be lesser than 0.1 per cent for treating the water used for larval rearing of fishes and the organic acid treated water may be used for larval rearing of fishes at lesser concentrations, since there is decline in pathogenic vibrio count. Further studies are necessitated to evaluate the concentration of organic acids on the survival of the fish larvae.