Stress responses of brown trout,Salmo Trutta L., to the cyanobacterium,Microcystis aeruginosa

Sublethal effects of exposure for 96 h to lysed cells of the cyanobacteria Microcystis aeruginosa PCC 7820 [a strain that is toxic by mouse bioassay and yields microcystins detectable by high-performance liquid chromatography (HPLC)], and M. aeruginosa CYA 43 (a strain that is nontoxic by the mouse bioassay and does not yield microcystins detectable by HPLC), on brown trout (Salmo trutta) were investigated. Exposure of fish (14–90 g) to lysed M. aeruginosa 7820 cells (24–42 μg microcystin-LR L−1; 288 μg chlorophyll a L−1) caused an increase in plasma cortisol levels. This response was biphasic with a 10-fold increase (t = 0, 8.87 ng mL−1) after 1 h, and a second significant peak after 8 h, before returning to normal levels at 96 h. Plasma glucose levels rose, reaching a peak after 8 h (from 65 mg 100 mL−1 to 116 mg 100 mL−1) before stabilizing. Plasma Cl− concentrations decreased after 4 h exposure; levels stabilized to control values. Plasma Na+ was not affected. For fish immersed in lysed M. aeruginosa CYA 43 cells (288 μg chlorophyll a L−1), plasma cortisol, glucose, and ion (Na+ and Cl−) levels did not significantly change over the 96 h period. It is concluded that fish respond physiologically to the presence of lysed M. aeruginosa 7820 cells and exhibit a classic stress response. Possible lethal consequences of these stresses are discussed.