Submitted to: Proceedings of Southern Weed Science Society
Publication Type: Abstract Only
Publication Acceptance Date: 2/17/1998
Publication Date: N/A
Technical Abstract: The blue-green alga Oscillatoria cf. chalybea,produces the monoterpene 2-methylisoborneol which can bioaccumulate in channel catfish (Ictalurus punctatus),imparting an undesirable, musty flavor. This is the first report of an attempt to discover an algicide that will selectively eliminate this alga in catfish aquaculture ponds and not affect the more desirable phytoplankton. A microtiter plate-based bioassay was developed and used to test both commercial herbicides and natural products for their effects on O. cf. chalybea and a representative green alga, Selenastrum capricornutum.Several compounds, both synthetic and natural, were found to be selective at low concentrations.In this bioassay,diuron, a herbicide being considered for use in catfish aquaculture, was not selective.Ferulate,a decomposition product of straw, was almost 1000-fold more toxic towards O. cf. chalybea than S. capricornutum. After consideration of potential toxicity, selectivity, efficacy, and cost, ferulate was chosen for field testing in the summer of 1997. Twelve earthen, 0.25 ha each (1,159kL) ponds at Stoneville,MS were each stocked with ca. 650 kg of catfish. Beginning July 29, after O. cf. chalybea was detected in several of the ponds, half of the ponds were treated weekly with sufficient ferulate to bring the concentrations in the ponds to 5 M (five times higher than the dose required for growth suppression of O.cf. chalybea in the laboratory). No toxic effects of ferulate on the catfish were observed. No dramatic effects on any phytoplankton populations were observed, and the effects on O.cf. chalybea populations were equivocal.We concluded that ferulate is not an effective, selective algicide for O.cf. chalybea in catfish ponds at the concentration that we used.