ANTI-PHYTOPLANKTON THERAPY OF FINFISH - THE MUCOLYTIC AGENT L-CYSTEINE ETHYL-ESTER PROTECTS COHO SALMON ONCORHYNCHUS-KISUTCH AGAINST THE HARMFUL PHYTOPLANKTER CHAETOCEROS-CONCAVICORNIS

The harmful diatoms Chaetoceros concavicornis and C. convolutus will k ill salmonids such as rainbow trout Oncorhynchus mykiss and coho salmo n O. kisutch if present at as few as 5 cells ml-1 seawater. Our previo us research has shown that the barbed spines of these diatoms become w edged between the secondary lamellae of salmonids, where they cause ex cessive production of mucus by goblet cells. This mucus and the diatom s accumulate on and between the secondary lamellae to such an extent t hat the fish suffocate. A class of pharmacologically active compounds (mucolytic agents, e.g. L-cysteine ethyl ester) exists which decrease mucus production in mammals and humans when ingested. When coho salmon ingest this agent at up to 12 mg kg-1 biomass d-1, mucus synthesis is reduced to such an extent that an accumulation of this material does not occur on and between the secondary lamellae; the fish remain viabl e in what would otherwise be a lethal exposure to C. concavicornis cel ls.