PHYSIOLOGICAL STRESS EFFECTS OF CONTINUOUS-DC AND PULSED-DC ELECTROSHOCK ON JUVENILE BULL TROUT

Juvenile bull trout Salvelinus confluentus exposed to continuous-or pu lsed-DC electroshock exhibited rapid elevations in plasma cortisol and glucose, but plasma chloride did not change. In a I-h experiment usin g 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 wi thin 15 min of a 10-s electroshock. Plasma cortisol reached a peak lev el of 156 +/- 15 ng ml(-1) at 45 min and then decreased, whereas plasm a glucose reached its highest level of 179 +/- 75 mg 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 respon se 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 con centrations declined thereafter, levels remained above control values at 24 h. Plasma glucose was elevated from 60-65 to 120-134 mg dl(-1) a fter Ih by both electroshock treatments and remained near or above tho se levels for the 24-h duration. Plasma cortisol and glucose levels we re much higher in electroshocked bull trout at Ih compared with those in fish lh after receiving a 30-s handling stressor (cortisol, 90 +/- 12 ng ml(-1); glucose, 82 +/- 6.1 mg dl(-1)). The results indicate tha t both continuous and pulsed DC were more stressful to juvenile bull t rout than handling and that recovery, at least for pulsed DC, may take longer than 24 h. (C) 1997 The Fisheries Society of the British Isles .