Biofoc technology system (BFT) is a microbial-based fish culture system that works by elevating the carbon nitrogen ratios in the culture unit. The biofloc composition, water quality and performance of aquatic animals, however, can sometimes depend on the added carbon source. Therefore, it is most likely that the carbon sources influence the microbial community in BFT. This study seeks to establish the effect of carbon sources on the structure and planktonic compositions of bioflocs.
A 21-day experiment was conducted in the wet laboratory of Universiti Putra Malaysia, using 50 L of water housed in 100 L capacity glass aquarium. Each of the 9 aquaria received 20 g of grinded fish feed (42% crude protein) at three days interval to have a similtude of aquaculture wastewater. Three different carbon sources, sucrose, glycerol and rice bran were experimented and added at carbon/nitrogen ratio of 15 in each tank with the experiment triplicated. The water quality was monitored daily and after 21 days, 50 ml of the biofloc water in each tank was collected for morphological examination, phytoplankton and zooplankton analyses using standard procedures.
The colours of the bioflocs from the different tanks were different, glycerol biofloc was greenish, sucrose biofloc tended towards reddish while rice bran biofloc was brownish in colour. The morphostructure of the bioflocs from different carbon sources as observed under microscope were different, though all the bioflocs had irregular agglomerates. The bioflocs in glycerol treatment were well dispersed. Sucrose and rice bran had aggregated structure, and it is more compacted in rice bran. The planktonic composition was also different among the different carbon sources. Phytoplankton from 18 genera and 5 phyla were observed (Figure 1). These include; Cholorophyta (Chlamydomonas, Palmella, Micractinium, Oedogonium, Dictyosphaerium, Coelastrum and Scenedesmus), Euglenophyta (Astasia), Ochrophyta (Gonyostomum, Fragilariopsis, Amphora and Tribonema), Charophyta (Coleochaete), Dinoflagellata (Peridinium and Ceratium) and Cyanobacteria (Anabaena and Gomphosphaeria). The phytoplankton abundance in the sucrose and glycerol treatments were higher compared to rice bran treatment. The glycerol treatment was dominated by Cholorophyta while sucrose was dominated by mixtures of Euglenophyta, Ochrophyta and Chlorophyta. Rice bran treatment had the least diverse and abundant phytoplankton with only four genera (Anabaena, Gomphosphaeria, Tribonema and Dictosphaerium). The sucrose treatment had in total of 13 phytoplankton genera while glycerol had 12 genera. The Dictosphaerium (Chlorophyta) was found in all treatments.
In general four groups of zooplankton were observed in the biofloc treatments which include; rotifers (Lecane and Lepadella), protozoa (Ciliate) and nematode (Figure 2). The glycerol treatment had most abundant zooplankton from rotifers, it also had some nematodes. The sucrose treatment had both rotifers and protozoa, but rice bran treatment had only protozoa.
The results in this study indicated that carbon sources affect both the morphological structure and microbial composition of the bioflocs.