Evaluation of the natural product SeaKleen for controlling the musty-odor-producing cyanobacterium Oscillatoria perornata in catfish ponds

The cyanobacterium (blue-green alga) Oscillatoria perornata is the major cause of musty off-flavor in farm-raised channel catfish Ictalurus punctatus in western Mississippi. Currently, the only federally approved compounds for use as selective algicides in catfish aquaculture ponds in the southeastern United States are the herbicide diuron and copper-based products (eg., copper sulfate). Due to environmental issues and the broad-spectrum toxicity of these synthetic algicides to nontarget organisms, there is a need for environmentally safe algicides for controlling O. perornata in catfish ponds. Laboratory bioassay screening of the natural product SeaKleen, a quinone-based biocide used to treat the ballast water from ships, found that it is selectively toxic towards O. perornata compared with the green alga Selenastrum capricornutum. Subsequently, efficacy testing of SeaKleen was performed using limnocorrals placed in catfish aquaculture ponds containing O. perornata blooms. Two studies were performed: a dose-response study and a single-effective-concentration study. For both studies, water samples were removed from inside the limnocorrals before and after the application of SeaKleen. These water samples were monitored for levels of the musty off-flavor compound 2-methylisoborneol (MIB), chlorophyll-a levels, and phytoplankton community structure. Results from both studies found that approximately 1.3 mg/ L SeaKleen was effective in significantly reducing the levels of chlorophyll a and MIB compared with controls. In addition, the abundance of O. perornata and other predominant species of filamentous cyanobacteria were significantly reduced compared with controls. Green algae and diatoms were not significantly affected. Additional studies are needed to determine the potential of SeaKleen as a selective algicide in commercial catfish aquaculture.