EXAMINATION OF ELECTROSHOCKING
INJURY IN HATCHERY RAINBOW
TROUT

MATT M. HUGHES
School of Science and Natural Resources
Lake Superior State University
Sault Ste.Marie, Michigan 49783  USA

December 12, 1995



Abstract.  Four groups of ten hatchery raised rainbow trout
Oncorhyncus mykiss were exposed to pulsed direct current from a
backpack electroshocker at two different voltages.  The
objectives of this study were to determine if there is a
difference in injuries between small (< 250 mm) and large (>250
mm) rainbow trout with 250 volts vs. 500 volts respectively.  I
used X-rays and necropsies to assess spinal injury and internal
hemorrhaging along the spinal column.  Of the 40 trout exposed to
electroshocking, 48% suffered spinal injuries often associated
with internal hemorrhaging.  Larger trout had significantly more
injuries than small trout (chi-square; P<0.05).  In addition to
the laboratory study, 12 fish collected by electroshocking at
Pendill's Creek followed this same trend.  I found no significant
difference between the two voltages used in the experiment.  I
conclude that the incidence of electroshocking-induced injury was
unacceptably high.  These injuries could result in death or
reduced growth rates that would bias common fishery assessment
methods such as age and growth or population studies based on a
mark-recapture technique.


Selected References

Pratt, Virgil S.  1954.  Fish mortality caused by electrical
shockers.  Trans. of American Fish Society. 84:63-68.

Sharber, N.G. and S.W. Carothers.  1988.  Influence of
electrofishing pulse shape on spinal injuries in adult
rainbow trout.  North American Journal of Fish Management.
8 : 117-122.