School of Applied Science, Temasek Polytechnic, Singapore, 529757, Singapore
The use of sweet potato, Ipomoea batatas flour as a carbon source for biofloc production in freshwater culture of tilapia, Oreochromis sp., was evaluated in terms of its effects on water quality, microbial population and fish yield. The experiment was conducted using 20 L glass aquaria with two sources of carbon, namely, wheat flour and sweet potato flour. Glass aquaria with no carbon source were used as control. The treatments and control were done in duplicate. Biofloc was produced in the glass aquaria for 10 days, followed by stocking of tilapia juveniles (ABW: 15 g) at a density of 4 fish/aquarium and reared for 30 days. During the rearing period, biofloc production was maintained by adding the different flours at a carbon:nitrogen (C:N) ratio of 16. Commercial feeds (35 % crude protein) were also given at 6 % body weight. Moderate aeration was provided in all aquaria to maintain the flocs in suspension. The levels of total suspended solids and biochemical oxygen demand as well as total heterotrophic bacteria and bacilli populations were significantly higher in the treatment groups than the control. However, the levels of nitrogenous wastes (ammonia-N, nitrite-N and nitrate-N) were generally lower in glass aquaria added with sweet potato flour. At the end of the experiment, there were no significant differences in the average weights of tilapias from the biofloc groups and the control, although the tilapias that were reared in the biofloc group with sweet potato flour had the lowest average body weight and growth rate. Tilapias from both biofloc groups had significantly lower feed conversion ratio compared with the control, with the wheat flour biofloc group performing better than the sweet potato flour biofloc group. Taken together, the results of this study showed that the bioflocs that are produced using sweet potato flour as a carbon source could lower nitrogenous waste in the rearing water and to a certain degree serve as food for tilapias in freshwater culture. Efficient feeding management is needed to ensure good growth of the fish if sweet potato flour is to be utilized for biofloc production.