Submitted to: Book of Abstracts Aquaculture America
Publication Type: Abstract Only
Publication Acceptance Date: 9/9/2011
Publication Date: 2/29/2012
Citation: Schrader, K., Green, B.W., Perschbacher, P.W. 2012. Development of phytoplankton communities and common off-flavors in a biofloc technology system used to culture channel catfish Ictalurus punctatus. Book of Abstracts Aquaculture America. p. 443.
Technical Abstract: The use of biofloc technology production systems continues to increase in the aquaculture industry worldwide. Recent research demonstrated that outdoor biofloc systems can be used to produce high yields of channel catfish (Ictalurus punctatus). However, studies have not yet been performed to determine the development and composition of phytoplankton communities and related off-flavor problems in these biofloc production systems. In this study, water samples were collected biweekly from May to November from nine 18.6 m2 biofloc culture tanks, and channel catfish samples were collected during harvest in November from the nine culture tanks. Water and catfish fillet samples were analyzed using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) for levels of the common off-flavor compounds geosmin and 2-methylisoborneol (MIB). The development and composition of phytoplankton communities in each culture tank was monitored microscopically using a Sedgewick-Rafter counting chamber and by measuring chlorophyll a concentrations. In addition, water and biofloc samples were evaluated to assess the microbial sources of geosmin and MIB within the culture tanks. Data of mean geosmin and MIB concentrations, chlorophyll a concentrations, and cumulative feed additions (g/m3) were analyzed by Pearson correlation analysis in order to determine significant relationships (p < 0.05) between the measured variables. Phytoplankton (including algae and cyanobacteria attached to bioflocs) biomass, as determined by concentrations of chlorophyll a in the water, gradually increased in all tanks over time. Phytoplankton communities that developed in the culture tanks were dominated by fast-growing, unicellular and small colonial types of green algae (chlorophytes) and diatoms (bacillariophytes) and slower growing, small colonial types of cyanobacteria (cyanophytes). Although geosmin and MIB were present in the culture water of each tank during most of the study, concentrations were typically low and only one tank yielded catfish with geosmin and MIB in their flesh at levels high enough to be designated as off-flavor. A positive correlation (p < 0.05) between cumulative feed addition and chlorophyll a concentration was found. In addition, a positive correlation (p < 0.05) between cumulative feed addition and MIB concentrations in the water of culture tanks was found and indicates a greater potential for MIB-related off-flavor problems at higher feed application rates. Although the microorganisms responsible for the production of geosmin and MIB in the culture tanks were not isolated and identified in this study, the potential microbial sources will be presented.