Invited overview: conclusions from a review of electroﬁshing
and its harmful eﬀects on ﬁsh
Darrel E. Snyder
Larval Fish Laboratory, Department of Fishery and Wildlife Biology, Colorado State University, 1474
Campus Delivery, Fort Collins, CO 80521-1474, USA (Phone: +1-970-491-5295; Fax: +1-970-491-5091;
Accepted 18 May 2004
Abstract page 445
Electrical ﬁelds and responses of ﬁsh 446
Harmful eﬀects 447
Factors aﬀecting injuries and mortality 448
Impacts on reproduction, embryos, and larvae
Summary – Recommendations 451
Key words: electroﬁshing, ﬁsh, injuries, mortality, responses, stress
These conclusions are extracted from a published review and synthesis of literature on electroﬁshing and its
harmful eﬀects on ﬁsh. Although a valuable sampling technique for over half a century, electroﬁshing,
which involves a very dynamic and complex mix of physics, physiology, and behavior, remains poorly
understood. New hypotheses have been advanced regarding ‘‘power transfer’’ to ﬁsh and the epileptic
nature of their responses to electric ﬁelds, but these too need to be more fully explored and validated.
Fishery researchers and managers are particularly concerned about the harmful eﬀects of electroﬁshing on
ﬁsh, especially endangered species. Although often not externally obvious or fatal, spinal injuries and
associated hemorrhages sometimes have been documented in over 50% of ﬁsh examined internally. Such
injuries can occur anywhere in the electroﬁshing ﬁeld at or above the intensity threshold for the twitch
response. These injuries are believed to result from powerful convulsions of body musculature (possibly
epileptic seizures) caused mostly by sudden changes in voltage as when electricity is pulsed or switched on
or oﬀ. Signiﬁcantly fewer spinal injuries are reported when direct current, low-frequency pulsed direct
current (£ 30 Hz), or specially designed pulse trains are used. Salmoninae are especially susceptible. Other
harmful eﬀects, such as bleeding at gills or vent and excessive physiological stress, are also of concern.
Mortality, usually by asphyxiation, is a common result of excessive exposure to tetanizing intensities near
electrodes or poor handling of captured specimens. Reported eﬀects on reproduction are contradictory, but
electroﬁshing over spawning grounds can harm embryos. Electroﬁshing is often considered the most
eﬀective and benign technique for capturing moderate to large-size ﬁsh, but when adverse eﬀects are
problematic and cannot be suﬃciently reduced, its use should be severely restricted.
Reviews in Fish Biology and Fisheries 13: 445–453, 2003.
Ó 2004 Kluwer Academic Publishers. Printed in the Netherlands.