Physiological stress effects of continuous- and pulsed-DC electroshock on juvenile bull trout

Juvenile bull trout Salvelinus confluentus exposed to continuous- or pulsed-DC electroshock exhibited rapid elevations in plasma cortisol and glucose, but plasma chloride did not change. In a 1-h experiment using 240 V at 1 times 4 A of 60-Hz pulsed DC (voltage gradient 0.81 V cm super(-1)), which proved lethal, plasma cortisol and glucose rose significantly within 15 min of a 10-s electroshock. Plasma cortisol reached a peak level of 156 plus or minus 18 ng ml super(-1) at 45 min and then decreased, whereas plasma glucose reached its highest level of 179 plus or minus 7 times 5 mg dl super(-1) at 1 h. In a 24-h experiment using lower dosages, plasma cortisol increased from 6 times 1-16 ng ml super(-1) to peak levels of 155-161 ng ml super(-1) in 1 h in response to a 10-s electroshock of continuous (130 V, 0 times 5 A, 1 times 45 V cm super(-1)) or pulsed (120 V, 0 times 5 A, 60 Hz, 0 times 55 V cm super(-1)) DC. Although plasma concentrations declined thereafter, levels remained above control values at 24 h. Plasma glucose was elevated from 60-65 to 120-134 mg dl super(-1) after 1 h by both electroshock treatments and remained near or above those levels for the 24-h duration. Plasma cortisol and glucose levels were much higher in electroshocked bull trout at 1 h compared with those in fish 1 h after receiving a 30-s handling stressor (cortisol, 90 plus or minus 12 ng ml super(-1); glucose, 82 plus or minus 6 times 1 mg dl super(-1)). The results indicate that both continuous and pulsed DC were more stressful to juvenile bull trout than handling and that recovery, at least for pulsed DC, may take longer than 24 h.