New Electric Fish Found, Are Wired Differently

Scientists who found two new species of electric fish in the Amazon River were stunned to discover that the two animals are, well, wired much differently.

Unlike their relative the electric eel, which can generate a charge of 600 volts, these weakly electric fish, called bluntnose knifefish, produce much smaller electric discharges.

The two new species and their electric discharges. Courtesy John P. Sullivan, PhD, Cornell Laboratory of Ornithology

While electric eels use their electricity to stun prey and deter predators, the newfound fish use theirs to navigate in murky waters: They live under floating rafts of vegetation along the margins of the Brazilian Amazon called “floating meadows.” (See more pictures of electric fish.)

They produce electrical pulses of a few hundred millivolts from a specialized structure in their tail called an electric organ.

This organ can sense distortions made by objects in the fish’s electric field. Like bats and dolphins that use echolocation to navigate by sound, electric fish use this system of electrolocation to sense the world around them.

Shocking Difference

freshwater species of the weekOne of the fish, Brachyhypopomus bennetti,  has a large electric organ and a short, fat tail. The other, Brachyhypopomus walteri, has a more typical electric organ and a long, thin tail.

But the most significant difference between the two is the type of electric signals they generate. Most electric fish, including B. walteri, produce electric signals with both a positive and negative phase: an alternating current signal. (See a picture of another species of electric knifefish.)

But B. bennetti is different. Its electric signals are more like direct current in that they have one phase rather than two, according to the study, led by John Sullivan of Cornell University.

A Tail of Two Species

Searching for the reason behind this difference, the team noticed many B. bennetti had the same injury: tails that were partially bitten off by predators.

“This species’ preference for floating-meadow habitat along the major channels of the Amazon River basin may put it at particularly high risk of predation and ‘tail grazing,'”—or losing a portion of its tail to a hungry predator, according to the study, published August 28 in the journal ZooKeys. (Pictures: “Into the Amazon” from National Geographic magazine.)

That’s bad news for most electric fish: Tail damage severely alters the electric signals produced by those species with alternating current signals. But B. bennetti‘s direct current signals were largely unaffected after their tails were partially bitten off by predators.

So the unusual electric signal of B. bennetti may have evolved to help it deal with frequent tail nibbling by predators in their habitat.

The authors suspect that even though sister species B. walteri lives in the same habitat, the fish didn’t evolve the single-current adaptation because it likely has a different lifestyle and behavior than B. bennetti—a topic for more electrifying research.

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Mary Bates is a freelance science writer living in Boston. She has a PhD in psychology from Brown University where she studied bat echolocation. You can visit her website at www.marybateswriter.com and follow her on Twitter at @mebwriter.
  • sylvestre lilly

    Looking at the voltage plots, one can see that the waveforms are representative of constructive interference aka ‘harmonics’. The alternating phase (walteri) represents either a complete octave type harmonic (a 1:2 ratio) interference (although the waveform is not ideally symmetrical) or a discrete portion of the next perfect harmonics (2:3 or 3:4).
    The other waveform plot (bennetti) indicates a positively constrained phase structure. This is interesting as it results from a unison type harmonic (a 1:1 ratio). The unison harmonic, phase-locks the waveform into one hemisphere (phase space) and is consequently represented as either singularly positive or negative (depending on the relative ‘spin’ of the interfering impulses).
    Essentially, phase constrained waveforms such as that of bennetti are indicative of a 1:1 harmonic interference.
    It would be interesting to know the relation between the two species developmentally/historically as well their existing biological parameters, I would venture to guess that comparative analysis of biological functioning involving the electrical organs and their natural frequencies would shed light as to the difference in waveforms.

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