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NMSU professor's study of knife fish is electrifying

When compared to other fish species, knife fish appear pretty typical. However, these Amazon natives, a type of weakly electric fish, are anything but ordinary.



New Mexico State University graduate student Robert Guth, demonstrates how electric signals and frequencies of knife fish are recorded using a electrode device created by NMSU students. (NMSU photo by Donyelle Kesler)

Graciela Unguez, professor of biology at New Mexico State University, and her team of seven student researchers, have been studying the fascinating attributes of the knife fish which are able to produce weak electric fields around themselves from a specialized electric organ that is derived from skeletal muscle cells and are also able to regenerate the spinal cord, skin, bones, muscle, blood vessels and electric organ.

"What we are most interested in is the development and plasticity of the nervous system and how cells can change and work to form certain behaviors," Unguez said.

Unguez, who began her study while conducting her post-doctoral work at the University of Texas at Austin, was amazed with the nocturnally active fish, found in the waters of South America, and their survival skills unique to any other type of fish.

Using electric fields as means of communication and navigation, knife fish are able to utilize specialized cells called electrolytes to produce electric currents. Some species of strongly electric fish, such as electric eel, are capable of producing up to 500 volts of electricity, strong enough to kill humans.

The fish studied in Unguez's lab produce weak electric fields, faint enough for them to be handled and studied. Their ability to produce these electric fields is essential for the fish's survival as it is their way of sensing their environment, choosing a mate and identifying other members of their own species.

In her lab, Unguez and her team have looked into how electrical activity that some tissues have regulates the identity and function of cells and how it can contribute to making different cells.

"Because we try to manipulate the electrical signal to better understand it, we need to know what the original electrical signal is that these fish emit," Robert Guth, a graduate student at NMSU, said. " One way we can do that is by recording the electric field these fish are producing."

Guth, who has been conducting research with Unguez for the last three years, explained how signals are recorded using an electrode device built by students in the laboratory, to visualize the electric field these fish are producing. By placing electrodes in the water, the electric field emitted by the fish can be recorded and characterized by its specific frequency.

"Once you move the electrodes towards the fish you can actually hear the signal from the fish and once you move away from the fish you can hear the signal fade." Guth said. "The pitch heard from one species of fish is different than the other species and that's one way we can distinguish between species since they use different frequencies."

"Classically, people don't think we have a lot of electrical tissue," Guth said. "We do have electrically active tissue, all of the brain tissue and muscle tissue are electrically active. So from that perspective, it's important to look at electrical activity and how it can affect the identity and properties of cells and tissues."

The second emphasis in Unguez's research is that of tissue regeneration. While lizards and amphibians are known to regenerate body parts, what Unguez says sets the electric fish apart is what exactly they regenerate.

"What makes regeneration in these fish different is the fact that they are able to re-generate spinal cord multiple times as adults," Unguez said. "We are looking at the stem cells in the fish, similar to stem cells we have, to find how these cells are able to do this."

According to the team's studies, the fish regenerate differently than salamanders or frogs. Instead of regenerating by de-differentiation where fully mature cells revert back to an undifferentiated cell, like a stem cell, these fish appear to use stem cells more then dedifferentiated to restore the lost tissues.

"What we think is different about this fish is the mechanism they use to regenerate, which is what we are investigating right now." NMSU alumna Veronica Salazar said. "Using a satellite cell or muscle stem cell, that we all have, the satellite cells the fish have are able to become any type of cell rather than just muscle."

Salazar, who has also been on board with the study for the last three years, has been closely examining regeneration in the Sternopygus macrurus or "sternos" species called gold stripe knife fish. By cutting off the tip of the fish tail, regeneration can be initiated in the fish and in a matter of three weeks, the sternos can have a fully functioning tail.

"This is important because if we understand how these cells work, we might be able to figure out how our cells can too, replace tissues and organs damaged by injury or disease,' Unguez said.