The Response of a Tropical Fish to Direct Current and Its 
Application to the Problems of Electrofishing in Sea Water ^ 
Morris E. Morgan^ 
Methods of electrofishing have been de- 
veloped successfully for use in fresh-water 
ponds and streams, but this equipment is not 
effective in sea water because the high con- 
ductivity of salt water greatly changes the 
power requirements (Smolian, 1944). If this 
obstacle can be overcome, it is reasonable to 
assume that electrofishing can be conducted 
in the sea with a success which would be at 
least equivalent to that experienced in fresh 
water. 
Electrofishing in fresh water is now widely 
practiced in Germany, the United States, and 
Canada, where it is used mainly as a new tool 
to supplement the facilities for study of fish 
populations. The progress made in Germany 
has been described by Smolian (1944) in a 
comprehensive report which includes a de- 
scription of the equipment and techniques 
used in that country. In the United States, 
the first efforts concerned with the reaction 
of fish to electrical stimulation centered 
around the development of electric fish screens 
and began as early as 1917 (Holmes, 1948). 
However, a method of actually collecting fish 
in fresh-water streams was first developed in 
1939 (Haskell, 1940). 
Equipment used for electrofishing in fresh 
water has consisted mainly of small, portable, 
gas-driven generators which produced alter- 
nating current. However, Smolian (1944) re- 
ported that the greatest effect seemed to be 
realized from using direct current interrupted 
at frequent intervals. Large fish were affected 
^ Contribution No. 34, Hawaii Marine Laboratory. 
Manuscript received July 2, 1952. 
2 Research Biologist, California Academy of Sciences. 
more strongly than small ones. There was 
also considerable variation in the sensitivity 
of various species to electrical stimulation. 
In reports from both the United States and 
other countries it has been emphasized that 
paralyzing, narcotizing, and attracting the fish 
can be accomplished only in the immediate 
vicinity of the electrodes. Outside this area 
the current merely irritates the fish and fright- 
ens them away. 
While some reports have been made con- 
cerning the injurious or fatal effects of elec- 
trofishing (Hauck, 1949), it appears that fish 
can be collected by using current strengths 
below those which will injure or kill. 
German scientists have been investigating 
the possibility of adapting electrofishing tech- 
niques for use in salt-water fisheries. At the 
present time it has been reported (Anon., 
1951) that they are in the process of installing 
electrical fishing gear on a boat of the type 
used in the trawl fishery. Only general news- 
paper-type reports have been published con- 
cerning this work. The basic research was 
financed personally by the scientists con- 
cerned so it is assumed that no detailed in- 
formation will be forthcoming until their 
work has reached a patentable stage. 
These reports indicate that their claims of 
success in the development of electrofishing 
equipment suitable for use in sea water are 
based on the more efficient utilization of elec- 
tricity rather than in merely increasing the 
amount. Special mention is made of pulse 
shape, pulse rate, and electrode arrangement. 
The response of living organisms to elec- 
trical stimulation was investigated as early as 
482 
