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 cyanobact eria 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 no ntoxic by the mouse bioassay and does not yield microcystins detectabl e by HPLC), on brown trout (Salmo trutta) were investigated. Exposure of fish (14-90 g) to lysed M. aeruginosa 7820 cells (24-42 mu g microc ystin-LR L(-1); 288 mu g chlorophyll a L(-1)) caused an increase in pl asma cortisol levels. This response was biphasic with a 10-fold increa se (t = 0, 8.87 ng mL(-1)) after 1 h, and a second significant peak af ter 8 h, before returning to normal levels at 96 h. Plasma glucose lev els rose, reaching a peak after 8 h (from 65 mg 100 mL(-1) to 116 mg 1 00 mL(-1)) before stabilizing. Plasma Cl- concentrations decreased aft er 4 h exposure; levels stabilized to control values. Plasma Na+ was n ot affected. For fish immersed in lysed M. aeruginosa CYA 43 cells (28 8 mu g chlorophyll a L(-1)), plasma cortisol, glucose, and ion (Na+ an d 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. Possib le lethal consequences of these stresses are discussed. (C) 1996 by Jo hn Wiley & Sons, Inc.