What is a fish? Field Museum curator Leo Smith talks about his research



A fish
  • Brocken Inaglory
  • A fish
Leo Smith, who's been an assistant curator of zoology at the Field Museum since 2007, has spent the last several months working on the upcoming exhibit "Creatures of Light: Nature's Bioluminescence," which opens this Thursday. Smith studies the evolutionary biology of fishes, particularly venomous and bioluminescent ones. He talked to me recently about his research and the upcoming exhibit; part one of the discussion focused on the "Creatures of Light" exhibition, the difference between bioluminescence and biofluorescence, and how male anglerfish become parasitic when they meet females. In this second part, he talks about what defines a fish, the ocean's "no-bone zone," and the first species he ever described. Smith, in his own words:

What people think of as fish fall into three main categories. The natural groups are the cartilaginous fishes, the sharks and rays; the lobe-fin fishes are the lungfish and the coelacanth. And then the ray-fin fishes, which is what everyone thinks about other than sharks. In order to say what is a fish you have to basically either include things like mammals, birds, amphibians, or you have to make some sort of distinction somewhere. You can do like, vertebrate that lives in water, but then you got whales and other things.

From an evolutionary standpoint, the fish is probably best thought of as including us and anything that crawled up on land. But it's complicated. I'm more closely related to a lionfish or a cichlid or rainbow fish or a trout than a trout is to a shark. We shared a more recent common ancestor with a trout than a trout did with a shark. A shark is like a second cousin once removed from a trout, and we're like brothers or something.

Leo Smith, doing fieldwork in Madagascar
  • John Sparks
  • Leo Smith, doing fieldwork in Madagascar
Most of the ocean is mid-water—you're not at the surface and you're not at the bottom. And the animals and plankton that live there will never see land in their whole life. When you look at it in terms of density, there's this little pocket called the deep scattering layer; it goes anywhere from about 1,500 feet to a few hundred feet. Every day it migrates: when the sun comes out it goes deeper, and when the sun goes away it goes back up, and it's because as you get closer to the surface, because of the sun and things like that, there's food. So it's worth this giant migration. The smallest things do this, so the slightly larger things do this, and everything does it. They got the depth of the ocean wrong in places because it was so dense with animals, they thought it was actually the bottom of the ocean.

Somewhere around 36,000, 37,000 feet, you lose vertebrates. Fish can't live down that far, because there's a point where you can't get calcium out of the water and back into a cell to make a bone—we jokingly call it "the no-bone zone" here.

[On one of the first species he described]

Everyone that went to work on it died—no one told me this when I first started, I was just some young kid and they were like, "Yeah, why don't you go describe that?"

What happened was, from what I can gather . . . this guy, Conrad Limbaugh, went out with a couple graduate students and they went into caves using this new scuba stuff that they had created themselves out of, like, soup cans. They went down, caught 40 or 50 specimens in a two-year period. So then they were working on the description and the primary author of the description, Conrad Limbaugh, was cave diving in France and he never came back. The species sat there for a few years and then a guy named Carl Hubbs, who was actually a curator here in like 1919, but was then a professor at Scripps Institution of Oceanography, he's like, "I'm gonna take over this thing." He was very prominent, probably published 750 papers. He went to go describe it and then he died. So the remaining ichthyologist in San Diego was just like, "I'm gonna put that on the shelf."

Then I was volunteering there, and he was turning 65, he was getting ready to retire. He was one of the original graduate students in the 50s that caught this thing, so he was like, "Before I die, I just wanna get that done." So he looked at me and was like, "Why don't you go describe this thing?" So we finally described it and both me and the other guy survived.

[On getting fish from pet stores]

Especially for the venomous fish that's just the easiest . . . it's really cost-effective. If I go to Guam or something, it's possible to get venomous fish. But a trip to Guam might cost the Field Museum $50,000, and maybe I'll come back with like 60 venomous fish. So I constantly keep an eye out for pet stores. I can get things from all over the world. The most I've ever spent is probably $300-$400. But even if it was $500, multiply that by that 50 and you're at half the price of the expedition.

Dr. Seuss Soapfish
  • Richard Pyle
  • Dr. Seuss Soapfish

The most exciting thing that ever happened to me is the first fish I ever described as new showed up on one of them about four months ago. It's a poisonous fish called a soapfish and it's actually this really cool, beautiful one called the Dr. Seuss Soapfish. We didn't name it that, we named it something like Reef Soapfish, something totally boring, and the aquarium word has renamed it the Dr. Seuss Soapfish, which is so much cooler. It's bright yellow and bright pink, it's got these polka dots, and the reason it's hard to get, the reason why we found it so recently, was that it requires you to go down about 400 feet. That's deeper than you can scuba dive.

There's people that describe fish all the time. But this one is weird and it's like the most expensive fish I've ever seen for sale. It showed up on this pet store a few months ago for $6,000. There's certain species, like strains of show koi, that can be the price of a Rolls-Royce or something, but of something that's gonna show up in an online pet store, this is the most expensive one that I've ever seen. I'm so proud that I described the most expensive thing. Although I think by the time it sold, they had dropped the price down to like $4,000.

"Creatures of Light" runs through Jan 5, 2014, at the Field Museum.

Add a comment