NOTE Koeller and Crowell: Electrotaxis in Homarus americanus 
629 
with 15°C seawater with a continuous flow-through 
system. Three EBP animals ranging from stage 4 to 
stage 8 (5-10 mm carapace length) were used in each 
trial, which is within the range of naturally occur- 
ring densities. Each animal was used only once. At 
least 24 hours before each trial the experimental 
animals were chosen randomly from a previously 
unused group kept in 15°C flow through holding 
trays. The animals were released directly above the 
cobble (into which they always disappeared within a 
few seconds) and allowed to acclimate overnight. The 
released animals almost always remained within the 
rock pile and were seen on the surrounding sand only 
on rare occasions. After each trial, all rocks were re- 
moved from the tank, uncaptured animals were re- 
covered, and the rocks were replaced haphazardly. 
This procedure produced a different configuration of 
burrowing locations and shelters for each trial and 
simulated the varied cobble habitat that would be 
encountered while sampling. 
The electrical apparatus (Fig. 1) consisted of a rec- 
tifier bridge, a capacitor, a 9-V battery, an opticoupler, 
and a power MOSFET transistor. A rheostat was 
used to regulate the AC power source. The bridge 
rectifies the current into and deposits a charge on 
the capacitor, thereby creating a DC source. A signal 
generator was used to control the opticoupler, which 
in turn controlled the gate of the MOSFET and pri- 
mary DC source by means of the 9-V circuit. All elec- 
trodes were made of stainless steel. The only vari- 
able was the electrode configuration, each configu- 
ration consisting of a particular combination of elec- 
trode shapes and locations. These included small 6.5 
cm 2 plates, 1.5-mm diameter braided wire in which 
a 2.5-cm length of the plastic insulation had been 
removed every 3 cm, or a combination of the two. 
The electrode configurations and the general experi- 
mental set up are shown in Figure 2. 
To determine if the number of captures between 
electrode configurations were significantly different, 
each trial of three animals was treated as a repli- 
Figure 1 
Circuit drawing of the electrofishing device (DC source in 
Fig. 2) used in experiments to determine electrotaxis and 
capture effciency in early benthic-phase American lobsters, 
Homarus americanus. 
cate in a one-way analysis of variance, with the num- 
ber of animals captured in each trial as the variable. 
Similarly, the capture time of the first, second, and 
third animal in each trial was treated as a replicate 
and a one-way analysis of variance was performed 
separately for each emergence. Differences between 
means were tested with the LSD post-hoc test. 
Results and discussion 
Preliminary behavioral observations in open tanks 
without shelters or substrate showed that a wide size 
range of lobsters (5-50 mm carapace length) reacted 
to the electric current in a similar manner. This in- 
cluded an initial period of agitation of up to several 
seconds in which the animal appeared to become 
aware of the stimulus. This was followed by reorien- 
tation of the animal to face the cathode, commence- 
ment of involuntary tail flicking, and a resultant 
movement towards the anode. Animals of different 
sizes tended to react somewhat differently to the 
same input voltage. Larger animals (>30 mm cara- 
pace length) tended to struggle and often managed 
to escape the electric current. Once escaped, these 
animals could usually be re-entrained and induced 
to reach the anode by increasing the current strength 
and thus the tail flicking reaction. Overstimulation 
resulted in the animal lying motionless for several 
minutes after the current had been switched off. All 
animals that were affected in this way revived after 
a few minutes, apparently without ill affects. Small 
EBP (<10 mm) animals nearly always became mo- 
tionless, usually lying on their backs, upon reaching 
the anode when it was situated on the substrate. If 
the electrode was elevated above the substrate, EBP 
animals gathered below it and remained motionless, 
but upright. When the current was switched off, they 
quickly escaped. EBP animals always reached the 
anode more quickly than large animals. In many 
cases the reaction was immediate and the anode was 
reached in less than a second. Mortalities of experi- 
mental animals (pre- and postexperimental) that 
could not be attributed to accidental mishandling 
were negligible (total of 3) during the period of ob- 
servation (60 d). 
We concluded that American lobsters exhibit a true 
electrotaxis, i.e. where an animal in a DC field is 
compelled to swim to the anode through involuntary 
muscular contractions. Electrotaxis is well known in 
fish (Lamarque, 1990), but has rarely been described 
in crustaceans. Saila and Williams (1972) observed 
tail muscle contractions in American lobsters sub- 
jected to currents (<38 V input), but no taxis was 
evident. Stewart (1974) concluded that similar tail 
