TWENTY-FOURTH ANNUAL EASTERN FISH HEALTH WORKSHOP Royal Pavilion Resort, Atlantic Beach, NC MARCH 9-11, 1999 Toxicity Of Chitosan Acetate For Rainbow Trout (Oncorhynchus mykiss) Cultured In A Recycle System Graham Bullock1, Vicki Blazer2, Scott Tsukuda1, and Steve Summerfelt1 1Freshwater Institute, P.O. Box 1889, Shepherdstown,WV, 25443. 2U.S. Geological Survey, Biological Resources Division, National Fish Health Research Laboratory, 1700 Leetown Road, Kearneysville, WV, 25430 Chitosan is a deacetylation product of chitin. It is used as a flocculent for sewage and brewery wastes, and as a chelator of heavy metals. In aquaculture, chitosan has been used as an immunostimulant for protection against bacterial diseases in fish, for controlled release of vaccines, and as a diet supplement. Chitosan has been generally considered to be non-toxic to animals, but when it was added to a recycle system at 1.0 ppm as soluble chitosan acetate to remove organic solids, we found it was acutely toxic to rainbow trout (Oncorhynchus mykiss). In controlled experiments to determine the extent of toxicity, we found that trout died after several hours exposure to 0.75 ppm and died in 24 h after exposure to 0.075 ppm. Exposure to 0.038 ppm resulted in mortality after six days exposure while exposure to 0.019 ppm resulted in no mortality after 14 days exposure. Histological examination of gills, skin, muscle, and internal organs indicated significant and consistent pathological changes only in gills. Lifting of lamellar epithelium, hypertrophy and hyperplasia of lamellar epithelial cells occurred in trout exposed to 0.019 and 0.038 ppm. In trout exposed to 0.75 or 0.075 ppm chitosan large areas of lamellar fusion were observed. These results show that the soluble chitosan acetate is highly toxic to rainbow trout even at low concentrations. Return to 24th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page