The Nature of the Beast (according to Susan McCarthy)

That fish can read you like a book

My sister had a fire eel (Mastacembelus erythrotaenia), Thomas, living in an aquarium near the refrigerator in which his food was kept. The food was tasty live tubifex worms.

Thomas spent most of his time lurking under and behind rocks. Some predators like Thomas find this a useful default activity, since you might be thinking about nothing at all when, Oho! prey wanders by, and because you are under the rock, they suspect nothing.

When Thomas detected my sister heading for the refrigerator he truly shone as a wily predator. If she was going for “a glass of milk and a salami sandwich” Thomas took no action. But if her intent was to take out tubifex worms for the eel, Thomas was somehow able to tell. He swam out of the rocks and wriggled back and forth enthusiastically just below the surface. (It is not clear to me whether fire eels salivate, but if they do, Thomas may have been drooling.)

We can't figure out how Thomas knew when my sister was after human food and when she was after fish food. This was not a matter of timing, since Thomas was fed irregularly, at any hour of the day, and not on all days. It will probably remain a mystery, since it is no longer possible to do experiments (on my sister, not on the fire eel) under the same conditions. (Was she walking differently? Was she wearing tubifex gloves? Was she glancing at the tank? She says not.)

Perhaps you wonder why Thomas was not offered salami. Salami is fatty and salty, and probably not particularly good for little fire eels. Unlike many fire eels, Thomas was a good neighbor who did not eat the other denizens of the aquarium. On his salami-free regimen he waxed mighty, getting to be over a foot long before he perished in a reckless expedition to travel outside the aquarium. He was found in a desiccated condition on the keyboard of a nearby computer.

Let that be a lesson to all of us.

Aquamuzak

Researcher Ava Chase had three large koi (a.k.a carp) in her lab. She wondered if they could learn to divide music into categories. The categories she chose were classical music and blues.

Chase rigged up a button and a fish-chow reward system in the tank.* First, Beauty, Oro, and Pepi learned to press the button when they heard 30-second excerpts from a John Lee Hooker tape, but not when   they heard silence. This went well, although the “characteristically hyperactive Pepi” was slow to get with the program. Then they learned to press a button when they heard a bit of John Lee Hooker (“Blues Before Sunrise”), but not when they heard a bit from Bach’s oboe concertos. Then the rules were reversed, and they had to press the button for oboe concertos and not for John Lee Hooker. Beauty and Oro caught on quickly, but Pepi took longer, with “substandard” performances at first.

The stimuli were broadened to see if the fish would lump other blues and classical recordings with the ones they’d already heard—would they treat Muddy Waters and Koko Taylor as being more like John Lee Hooker than Bach? Would they lump Handel and Mozart with Bach? Yes and yes.

But there were Vivaldi problems. The koi took the view that Vivaldi’s guitar concertos were blues. They were adamant. So Chase used a 200-Hz high-pass filter to remove the lowest frequencies, in case they were picking these up through their lateral-line organs. This changed their outlook on the nature of Vivaldi, even after Chase turned off the filters. Chase notes that “Vivaldi evidently can impress listeners in odd ways. Porter & Neuringer, 1984, reported that a Vivaldi violin concerto sounded more like Stravinsky than like Bach to their pigeons, as it did also to some humans.”

(I pause to say that while I think this research is funny, I also think it is interesting. I reject the notion that all research must be no more than two obvious steps from curing Alzheimer's by giving urban youth jobs supplying unlimited clean energy.)

Later, Chase tested the carp with synthesized versions of music they had previously heard. First she refreshed their memories by exposing  them to a Bach oboe concerto and John Lee Hooker doing “One  
 Bourbon, One Scotch, and One Beer.” At this point Pepi “ceased  responding...and had to be dropped from the study.” (Chase doesn’t speculate as to what pushed Pepi too far, but we might guess. I have a collection of oboe jokes I think this fish might enjoy.)

Chase tested Beauty and Oro to see if they could distinguish between two melodies with identical notes and timbres, by giving them a choice between two versions of a synthesized passage of the theme from Paganini’s 24th Caprice for violin—one of which was played in reverse. This too is something that carp can do, or at least something that Oro could do, since “Beauty’s performance inexplicably deteriorated to the point where he had to be dropped as a subject.”

A possibility raised by this research is that the fish had not simply learned to discriminate between two musical selections (“the louder one,” “the one with the high note,” “the fast one”) but to form and assign categories (“blues,” “classical,” “tadpolesque,” “that weirdo Vivaldi”) to music.

That interests me, but I also wonder what was going on in with the koi. Were they bored? Were they losing their minds? Were they angry that they never got to hear the whole concerto? Were they anxious to find out why the guy is leaving home before sunrise? Were they frustrated that no one would produce a demo of Oro's composition, “Mean Mistreatin' Fish Teasin' Gal”? Were there quality control issues with the fish chow?

I call for more research.

*Chase, Ava R. 2001. “Music discriminations by carp (Cyprinus carpio).” Animal Learning and Behavior 29: 336–353.