THE EFFECTS OF THE CYANOBACTERIUM MICROCYSTIS-AERUGINOSA, THE CYANOBACTERIAL HEPATOTOXIN MICROCYSTIN-LR, AND AMMONIA ON GROWTH-RATE AND IONIC REGULATION OF BROWN TROUT

Brown trout were exposed for 63 days to five treatments: a control; th e purified cyanobacterial hepatotoxin microcystin-LR (MC-LR)(41-57 mu g MC-LR 1(-1)); lysed toxic Microcystis aeruginosa cells (41-68 mu g M CLR 1(-1) and 288 mu g chlorophyll a 1(-1)): ammonia (65-325 mu g NH3 1(-1)). All treatments produced significantly reduced growth compared to controls (P<0.05, Fisher test). Exposure to ammonia resulted weight loss over the first 7 days followed by weight increase, though at a s ignificantly lower level than in the other treatments. First exposed t o lysed toxic M. aeruginosa cells, or ammonia showed a significant inc rease compared to control fish or those exposed to lysed non-toxic m. aeruginosa cells. There were no significant differences in Na+ efflux or net Na+ uptake rates between treatments. Significant increases in b ody Na+ and Cl-= were seen in fish exposed to lysed toxic M. aeruginos a cells or ammonia. Only fish exposed to ammonia showed a significant increase in body ammonia. Short-term exposure over 4h to lysed toxic c ells, non-toxic cells or purified MC-LR resulted in insignificant chan ges in Na+ flux rates compared to controls although there was signific ant net Na+ loss in fish exposed to ammonia. Chronic exposure of fish to toxic cyanobacterial blooms may result in ionic imbalance and reduc ed growth.