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> A variety of fish can sense electrical fields. it is now understood how the mechanism works:
> 
> http://www.the-scientist.com/?articles.view/articleNo/48748/title/How-Skates--Sharks-Use-Electricity-to-Sense-Prey/&utm_campaign=NEWSLETTER_TS_The-Scientist-Daily_2016&utm_source=hs_email&utm_medium=email&utm_content=44122546&_hsenc=p2ANqtz--oNbX-7x3Y2HPvWYSfOoP_XdYtSiea4ESSH8rCC96iwpSiqPM20koOB5oOAhlFHP6nh9xTMflBNmCnDq55Sj8QcqBPOA&_hsmi=44122546
> 
> "Sharks, rays, and skates can detect minute fluctuations in electric fields—signals as subtle as a small fish breathing within the vicinity—and rely on specialized electrosensory cells to navigate, and hunt for prey hidden in the sand. But how these elasmobranch fish separate signal from noise has long baffled scientists. In an environment full of tiny electrical impulses, how does the skate home in on prey?
> 
> "In a study published this week (March 6) in Nature, researchers at the University of California, San Francisco (UCSF), have analyzed the electrosensory cells of the little skate (Leucoraja erinacea). They found that voltage-gated calcium channels within these cells appear to work in concert with calcium-activated potassium channels, both specifically tuned in the little skate to pick up on weak electrical signals.
> 
> ***
> 
> "Every time a fish breathes, seawater contacts the animal’s mucus membrane and generates a minor electrical field. Skates and other elasmobranch fish evolved to pick up on these electrical blips and use them to find hidden prey, navigate treacherous waters, and avoid undesirable fish.
> 
> ***
> 
> "Bellono and colleagues first isolated electrosensory cells from little skate ampullary organs. “These are tough experiments,” Julius said. “The cells in these ampullary organs are very small and hard to get out. The technical aspect of this was actually quite challenging.” The researchers then measured ionic currents within the cells in response to different electrical stimuli. “We found that there were these two major currents, a calcium current and a potassium current, coupled to one another,” Bellono said, noting that these currents amplify small electrical signals. The team then carried out gene expression experiments to confirm the presence of specialized calcium and potassium channels within the cells. “We were trying to close the gap between genetics and physiology,” Julius said.
> 
> "In a final experiment, the researchers used drugs to block these channels in several skate specimens, and compared their hunting abilities to those of wild-type skates. The team then hid electrical apparatuses under the sand in a skate tank, and watched as wild-type skates homed in on the signal while the altered skates did not. “In perfect world you’d use genetics, like in mice, and you’d knock out the genes of interest and ask if you’ve perturbed this behavior,” Julius said. “In skates we can’t do this, so we used the next best thing to block the ion channels—pharmacology.”
> 
> ***
> 
> "Christopher Braun of Hunter College in New York City agreed. “It’s really interesting, because it shows a mechanism of tuning that adjusts the sensitivity of those electroreceptor cells to the stimuli that the animal cares about,” he said. “The ionic mechanisms the paper describes make it very clear how the cells can be specifically tuned into those stimuli that are ecologically relevant.”
> 
> "Braun added that his own work focuses on how animals sort stimuli, and differentiate between their own electrical discharges and that of other animals. “That difference is often based on frequency,” Braun said. “The cellular mechanisms described in this paper provide a very low level way for the brain to only receive information that’s important to it, and not be distracted by other information.'”
> 
> Comment: Evolved or designed? If not present at first, how do the fish get to sense prey and eat? Seems to be irreducibly complex and had to be a saltation.