If I’m not mistaken, electric eels and rays mostly stun their prey with shocks of extremely short duration (maybe less than a second… I’ll have to look it up). I’m not sure they’re capable of even keeping a light bulb lighted (is it possible the pet store owner only claimed they were powering the system? Although I guess if there were many eels in the tank, it’s possible).
I’m not sure if this has anything to do with protecting themselves from shocks, but electric rays will bury themselves in the bottom, with only the electric organs and possibly the eyes showing, until something happens along to get shocked.
I think this thread’s been dried out of material for puns, but the groans will last for a long time…
OK, here’s some data on Electrophorus electricus, the electric eel. There are also electric rays and catfishes this information may not apply to.
Maximum recorded voltage: 550 volts (at 1 amp). This was recorded for a 2 m long fish (the size of the fish is related to the size of the electrical discharge).
Length of pulses: a few milliseconds, so it’s not long enough to heat up the filament on a lightbulb.
These discharges are usually not used to kill, but to either stun prey or convince threating organisms to go elsewhere.
While powerful enough to knock a person down, it’s unlikely electric eels could kill a person.
From: Paxton, J. R. and Eschmeyer, W. N. (Eds.). 1994. The Encyclopedia of Fishes, p. 112
Sorry, it doesn’t say how they keep from electrocuting themselves, but I think Markxxx’s webpage had a good hint on the issue.
My understanding of electric eels (which is a bit rusty) says that they have numerous parallel rows of eletricity generating cells down the lengths of their bodies. As they rows are parallel, the voltage through them is shared so if there are 100 rows (not an unreasonable amount) each cell will receive no more than 6V, a survivable amount.