High Voltage: Electric Fish switches between AC/DC

Two electric fish from the Amazonian Rainforest share many characteristics except for their current. The Brachyhypopomus walteri uses alternating current and the Brachyhypopomus bennetti uses direct current. These two types of knifefish were often mistaken for one another but graphs of their electric organ discharges (EOD) show otherwise. The Brachyhypopomus walteri has a longer, thinner tail that produces positive and negative waves while the Brachyhypopomus benneti has a shorter, thicker tail that only produces positive phase EODs.
These fish can communicate with their EODs by producing weak electrical discharge and electrolocate with special receptor cells in their skin to detect electric distortions in the water. The Brachyhypopomus benneti has a larger electric organ and produces the monophasic direct current while the Brachyhypopomus walteri has a more average organ (size doesn’t matter, fish) producing an alternating current.
The lead author and curatorial affiliate at the Cornell University Museum of Vertebrates John Sullivan says, “The most striking differences between these two similar species have to do with their electric organs and their electric organ discharges.” Researchers have recorded the sounds underwater made by the electric fish and the Brachyhypopomus walteri produces a sound like “pop pop”. This is done to help cloak the fish from predators. The Brachyhypopomus benneti rarely exhibit their electric organ discharge because it is only a positive monophasic pulse so the direct current cannot be canceled out. The Brachyhypopomus benneti is the only fish in the Brachyhypopomus family to have a monophasic phase for their electric signals. Researchers find this quite peculiar and have suggested that it is to mimic the electric ell, which has a powerful charge for stunning prey and protecting itself. The mimicry of the electric signals from the Brachyhypopomus benneti closely match that of the electric eel and makes the fish less desirable for predators.
One characteristic that both fish share is that even when caught, parts of their tails have been bitten off but they do regenerate. For the Brachyhypopomus walteri and all fish with biphasic current, they negative phase comes from their tail. Shockingly, the electric fish with the biphasic current suffer from a severely altered EOD after injuries. Researchers speculate that this provides a direct explanation for the difference in tail shape and size, where the Brachyhypopomus benneti can maintain communication and electrolocate in spite of tail injuries because of their monophasic current (DC).