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Archive for September, 2010

How Do You Catch a Fish that Eats Wood?

Posted by Richard Conniff on September 6, 2010

Paulo Petry with the one that didn’t get away

Here’s a nice interview about species discovery from the Nature Conservancy’s Cool Green Science blog:

An armored, Amazonian catfish. That eats wood from fallen logs — and, when desperate, the feces of its fellow catfish. With teeth shaped like spoons to make the eating easier. And oh, it’s a new species.

You gotta know more, right?

It’s all in a day’s work for Nature Conservancy freshwater scientist Paulo Petry, who with colleagues netted the first whole specimens of the species several weeks ago on a scientific expedition to the Fitzgarald arch, one of the remotest parts of the Peruvian Amazon — a region bursting with biodiversity, but also under threat from development.

I caught up with Dr. Petry to find out more about the fish, why the region is so special, and why discovering new species isn’t such a big deal … once you’ve done it a dozen times or so.

Cool Green Science Blog: Let’s first talk about this fish — it’s not pretty, is it?

Paulo Petry: Beauty is in the eye of the beholder. I have scientist friends who do work on the blobfish, and they think it’s beautiful!

How big are these specimens, and where did you find them?

The largest one is about 65 centimeters, the other two are half that size. They were caught at the confluence of the Purus and Curanja rivers. The Curanja is a tributary to the Purus River in Peru.

Why is it armored?

There are 35 different families of catfish on Earth. Armored catfish are unique to South America. They’re the most diverse group of catfish in South America — probably close to 800 species. They’re a fairly evolved, and a very specialized group within catfish.

How unusual is it to find a fish that eats wood?

There’s a very small group of catfish that do that. Some fish burrow into logs, but fishes that specialize in eating wood is a very small group. The ability to digest wood comes from a protozoan that lives in their intestinal tract. It’s able to convert the wood cellulose into a different kind of sugar that can be assimilated.

That’s one of the biggest issues when people bring these fish into the aquarium trade — they let them starve for very long times for shipping, the protozoan in their belly dies, and then they can’t digest wood. If you put another fish from the same group that is in good condition in the tank with them, the starving fish will eat the feces of the healthy fish to reinoculate itself with the protozoan, and then it will be able to eat wood and survive.

Yummy! Had local people known about this fish before, or was the discovery of the fish a true discovery for humanity and not just science?

Local people eat it. In the area in which we found it, it’s largely indigenous communities in this large park. These are the Nahuan people. They have five different ethnicities; the one we work with is the Sharanahua (which means “the good people”). They call the fish Ishgunmahuan — which in their language basically means “large armored catfish.” In Spanish, it’s “carachama gigante.”

There are 10 species of this genus called Panaque, and all of them have this commonality — they feed on wood and they have these particular kind of teeth, shaped like a spoon that allows them to scrape wood. These species are distributed in the Magdalena Basin, the Oronoco Basin, and the Amazon basin. There are two of them that seem to be more widely distributed, but the others are endemic to catchments in the Orinoco or the Amazon.

The interesting thing with this particular fish is that there were three specimens collected on the other size of the Amazon, and those fish were collected by shooting them. The locals shot them, caught them and dried them, leaving just empty shells. The particular specimens that we captured are the first that are fresh specimens, so we have the entire fish from which to take tissue samples.

They seem to be really tough to find and catch. You have to catch them with gill nets or cast nets, or shoot them. Since they eat wood, you’re not going to catch them with a line.

How did you know the ones you caught were this particular species?

We had seen those three specimens in Lima that looked alike, and the size. You look at the shape of the head — there are a bunch of characteristics that help you distinguish which species it is. Either it’s one that’s known, or it’s a brand new one. In this case, we knew it was still a new one, regardless. When we got back to Lima, we compared it to the other specimens.

Here’s an interesting statistic: There are 4,700 freshwater fish species in South America right now. On average, over 100 species per year have been discovered. This year alone, 69 new species have been described thus far. These numbers show very clearly that we are far from knowing the number of freshwater species in South America.

You’re part of a three-year National Science Foundation project to survey and document the aquatic fauna of the Alto Purus region, where this fish was discovered. Why is the Alto Purus region so poorly known? Why is it important to study?

It’s poorly known because it’s probably the most remote region within the lowland regions of the Amazon.

It’s significant ecologically because it is the drainage divider between four river major basins. The continent has gone through a very long time landscape evolution because of the Andes uplift. There used to be a very large basin, and that basin got split into three basins. That made the region core for a very large number of species.

After the basin got split, things started to divert — the split generated a lot of different kinds of habitats, from flat lowland plains to steep uphill streams, and the species adapted to all these niches and diversified. Since South America didn’t suffer from extensive glaciation, there have been very few environmentally led extinction events on the continent over time.

The Peruvian government created the Alto Purus National Park, but since very little is known about the park, there has always been doubt about its biological importance. We’re trying to show that the park represents a very important area for fish diversity and other aquatic animals. And we’re finding that the number of species of invertebrate groups is very high and their diversity far greater than was expected.

There are also some looming threats to the region, right?

Yes. There are several proposed infrastructure development projects, roads — with them will come lumber extraction, cattle ranching and slash-and-burn agriculture. Because the entire area is formed by fine sediment soils, if you do any land-use change and alter the forest coverage, you will have very strong erosion processes happening. It’s already prone to erosion naturally; if you change it to something else, it will get a lot worse.

There’s also significant opposition from indigenous communities in the area to the roads — they know that they bring new problems, diseases and environmental degradation. Right now, it’s fairly isolated there. There are just two flights a month there from Peruvian Air Force to provide supplies. The other way to get in is by river, which is a very long way. We chartered a flight in there, flying over the most pristine rain forest you will ever see.

I would imagine this isn’t the only species you expect to discover as part of this project.

We’ve found a lot of very small things like minnows and catfish that you need to look at very carefully under the scope and compare it with known species; I would expect that we will have a few new species that come out of the material we collected. Up to now we have for sure three new ones, two catfishes and a small tetra, but I expect that more will be diagnoses down the road.

How many species have you discovered in your career?

I have 11 sitting in my docket to be described right now. I don’t have the time right now, the manuscripts are in various degrees of completion, some in very early stages of preparation and some almost done. Since the Conservancy doesn’t do direct biodiversity documentation anymore, I do this on the side on weekends.

So, it’s not like you’re keeping track with notches on your bedpost or something like that?

If I discover something, I will send the material to a specialist that works on the group. He will describe it. Over the years, I send stuff in, and they worked it out.

Posted in The Species Seekers | Leave a Comment »

 
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