Effect of Different C/N Ratios on Volume and Potential Microbial Composition of Flocs in Prawn Culture System

Abstract

The use of ecofriendly method in the culture of aquatic organisms is increasing with demand as an advanced mode of aquaculture for gaining environmental sustainability. The present study was conducted by developing biofloc technology as one type of ecofriendly mode of aquaculture to evaluate the effects of C/N ratio on the volume of floc as well as on the load of several potential microbes in the floc composition. The experiment had three treatments with C'N ratios, 10, 15, and 20, namely TI, T2, T3 and a control (C). Determination of floc volume and enumeration of both some beneficial (Enterococcus spp., Clostridium spp., Lactobacillus spp.) and harmful (Salmonella spp.) bacterial load was done in the floc content of the fresh water prawn (Macrobranchium rosenbergii) culture tanks. Volume of floc was measured by using Cone and each of the bacteria was cultured by using specific and selective media. The results of this study demonstrated that T2 and T3 bad higher floc volume compared to control e and Tl (P<0.05). This higher growth in C/N, 15 and 20 might be due to available carbon sources for heterotrophic bacteria to remove environmental nitrogen given by feed supplements. In addition, the loads of Enterococcus spp. was found to be highest in T2, followed by Tl and C, and T3 (P<O.05). Lower Enterococcus spp. load in T3 might be due to high organic load that might deteriorate the environmental quality for this bacterial growth. However, in case of Clostridrium spp. we did not find any different between the treatments (p<0.05). Moreover, higher Lactobacilllus spp. load was in TI and T2 compared to T3 and C, which indicates that growth of Lactobacillus spp. require a fair range of carbon source, and lower and higher carbon load might be insufficient and!/or toxic for their growth. Finally, presence of no Salmonella spp. indicates a healthy culture system without any contamination, and/or might be due to competitive exclusion or inhibitory activities of beneficial bacteria against pathogenic bacteria. In conclusion, biofloc technology might be a good approach of sustainable prawn aquaculture through application of proper C/N ratios and further research should be conducted for more advance biofloc based aquaculture.