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 1·4 A of 60‐Hz pulsed DC (voltage gradient 0·81 V cm−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 ± 18 ng ml−1 at 45 min and then decreased, whereas plasma glucose reached its highest level of 179 ± 7·5mg dl−1 at 1 h. In a 24‐h experiment using lower dosages, plasma cortisol increased from 6·1‐16 ng ml−1 to peak levels of 155–161 ng ml−1 in 1 h in response to a 10‐s electroshock of continuous (130 V, 0·5 A, 1·45 V cm−1) or pulsed (120 V, 0·5 A, 60 Hz, 0·55 V cm−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−1 after 1h 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 ± 12 ng ml−1; glucose, 82 ± 6·1 mg dl−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.