Effects of purified microcystin-LR and cell extracts of Microcystis strains PCC 7813 and CYA 43 on cardiac function in brown trout (Salmo trutta) alevins

Sub-lethal cardiac responses of brown trout alevins (Salmo trutta L.) were determined in response to aqueous extracts of the cyanobacterium Microcystis strains PCC 7813 (microcystins detectable by HPLC) and CYA 43 (no microcystins detectable by HPLC) and to the purified cyanobacterial hepatotoxin, microcystin-LR (MC-LR) at concentrations of 5, 50 and 500 mug microcystin-LR equivalents l(-1). Responses were determined using a flow chamber and video camera attached to a low power microscope. Heart rate in brown trout alevins was acutely sensitive to cyanobacterial extracts and significant increases were observed within 15-60 sec of exposure to aqueous extracts, although no change was observed on exposure to purified MC-LR. Stroke volume increased in all treatments at 50 and 500 mug MC-LR equivalents l(-1), which may, at least in part, have been due to vasodilation of the yolk-sac blood vessels. Cardiac output increased significantly at all three concentrations of cyanobacterial cell extracts but not at the lowest concentration of MC-LR, although the rate increased at levels at/or above 50 mug l(-1). Increased heart rate, stroke volume and cardiac output occurred at environmentally relevant microcystin concentrations of Microcystis PCC 7813 and CYA 43 aqueous extracts.