World Aquaculture Magazine - June 2020

64 JUNE 2020 • WORLD AQUACULTURE • WWW.WA S.ORG There was no significant effect of salinity on biofloc productivity or protein content, which was around 40 percent. Accordingly, biofloc technology can be applied to fresh and sea water with the expectation of obtaining similar results. Overall, the proximate composition of bioflocs produced in these studies was 39 percent protein, 30 percent carbohydrate, 1.1 percent lipid, 13 percent crude fiber and 18 percent ash. Proximate composition of bioflocs can vary substantially: 12 to 49 percent protein, 18 to 36 percent carbohydrate, 0.8 to 16.2 percent fiber and 13 to 46 percent ash (Emerenciano et al . 2013). The crude lipid level of bioflocs produced was within the range of those previously reported (Kuhn et al . 2010). Tacon et al . (2002) suggested that the high ash content of biofloc is probably related to the presence of acid insoluble oxides and mixed silicates. Biofloc Imaging Awater sample from the seawater tank was taken. The sample was examined with a light microscope and different microorganisms were identified. Flocs varied in size ranging from 50 to 200 μm (Fig. 6). Six groups of organisms were identified: chlorophytes, diatoms, dinoflagellates, nematodes, rotifers, and cyanobacteria (Fig. 7). The bioflocs produced in this study were a mixture of bacteria (floc-formers and filamentous bacteria), particles, colloids and dead cells. There were a high abundance of chlorophytes, nematodes and rotifers. Nematodes were observed feeding on the flocs in fresh samples examined under the microscope. This result is similar to microbial communities in minimal- exchange, intensive aquaculture systems where the abundance of chlorophytes was higher than diatoms and heterotrophic dinoflagellates (Ray et al . 2010). They attributed the reason to the competition for resources existed between chlorophytes and diatoms. On the other hand, nematodes and rotifers were observed grazing on the floc particles. Such observation reflects the vitality of the biofloc community in which the interactions between organisms take place. Cyanobacteria were detected by fluorescence microscopy. This finding has been documented by other studies (Azim et al . 2008, Ray et al . 2010). Conclusion Biofloc technology has been used as a promising alternative grow-out technique and a method for obtaining protein for diets that originated from the diverse microorganisms. The present study aimed to produce an inexpensive biofloc meal that could be used in aquaculture systems and to evaluate its nutritional characteristics under fully controlled conditions. The biofloc produced using the rice meal as the organic carbon source had good nutritional value and is economically cheaper than the other organic carbon sources in Egypt. Overall, the study showed that the nutritional composition of biofloc can be sufficient to omnivorous organisms in terms of satisfying their needs of protein and essential amino acids. Analyzing factors affecting other nutritional parameters such as fatty acid profile and vitamins that are important in fish or shrimp nutrition are of interest. Biofloc technology will enable aquaculture grow towards an environmental friendly approach. Consumption of microorganisms in BFT reduces feed costs. Also, microbial community can rapidly utilize dissolved nitrogen leached from shrimp feces and uneaten food and convert it into microbial protein. These qualities make minimal-exchange BFT system an attractive alternative to extensive aquaculture. Biofloc might partially replace protein content in diets or decrease dependence on fishmeal. Notes Aya S. Hussain, Visiting Scholar at the School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, FIGURE 6. A light-microscope image of a 14-d old bacterial floc. FIGURE 7. Composition of biofloc: biofloc particle (A), chlorophytes (C), nematode (N) and rotifers (R). The protein content of biofloc decreases as C:N ratio increases. A high C:N ratio produces more biofloc but it is of lower quality as a potential nutritional supplement for shrimp or fish.