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Fish in the Congo -

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Fish in the Congo

The Congo is a large meandering African River. The lower Congo is different. This occurs after the
river spills over the side of a raised plateau and flows to the Atlantic Ocean. From Kinshasa to
the ocean is about 200Km, and here elevation changes 280 metres producing very fast rapids. The
river drains central Africa and this river passes through a narrow gorge. It's an extreme river
system. Over 300 species of fish are found in the rapids. Melanie Stiassny says the gorge drives
evolution of fish in this region.


Robyn Williams: and, as he said, the Mekong is vast. But so is the Congo River. Just listen to the
way Melanie Stiassny describes where she works and where she finds hundreds of new species.

Melanie Stiassny: Most of the Congo is a huge lazy, enormous river that flows and meanders on a
plateau. It goes through forest, it goes through savannah, it's the kind of classic big African
river, the kind of African Queen type of river. It's lazy and it's huge. And the part of the river
that I'm working on is in many ways a part that's kind of been forgotten or it hasn't been featured
in the same way that the rest of the Congo has, at least in people's imagination, it's called the
Lower Congo.

The Lower Congo is so different because basically what happens is the Congo flows over what's
called the high plateau of Africa, spills over a sill, as it were, and plunges down towards the
Atlantic Ocean. It's about 230 kilometres in length, so it's actually very, very small considering
the huge size of the Congo, but it drops from Kinshasa down to a town called Boma which is at the
mouth of the Atlantic. It drops in elevation about 280 metres. That's a huge drop over 350
kilometres. It's almost precipitous but it doesn't go in one single drop, it's kind of stepped. So
what that means is a whole series of just amazing rapids. So you have some of the fastest water in
the world, you have just the most spectacular rapid systems in the world. It's really, really an
extraordinary system, it's a very extreme system.

Where the Congo falls over this sill there's a huge gorge and it suddenly tumbles down into that
gorge. So you have all of the water that's basically draining most of central Africa, you know,
over 1.5 million square miles of drainage, so lots of water, is suddenly funnelled down through
this very, very narrow sill into a gorge.

Robyn Williams: It must be quite a challenge to work in for you.

Melanie Stiassny: It's a huge challenge, and I've been working there for quite a while now and I'm
really...I cannot tell you that I've even scraped the surface, and I'm collecting huge numbers of
species. I've recorded over 300 species so far, just in that tiny stretch. That's incredible. And I
think what we're seeing is how the river itself is really driving evolution, it's driving
diversification. We've got this kind of evolutionary playground.

Robyn Williams: Of course we're in your laboratory at the museum here in New York, and dozens and
dozens of bottles of fish which presumably come from there, you've collected. Are these all new
species or familiar ones or what?

Melanie Stiassny: Yes, I've got tonnes of dead fish here. All my friends say that I should be
moving on to chips any day. But yes, a lot of fish that you see around you, yes, a lot of them are
new species or species that are currently being described as new to science. Obviously most of
these fish aren't new to the Congolese people who rely on the river and its resources for their
livelihoods, but they don't have scientific names. So the rest of the Congo you can think of it as
a source, they get swept over that sill and they plunge down into the Lower Congo. Once they're
there, they can't get back, so they find themselves in this new environment, and some of them are
able to establish a population there and they're kind of fixed to a very local region because they
can't move around because the river is divided up by lots of rapids, and maybe they'll develop into
new species.

Robyn Williams: Any surprises yet? Any particular species that made you think 'wow'?

Melanie Stiassny: Yes, all of them make me think 'wow' because they're very, very cool and very
weird, many of them have extraordinary anatomical adaptations as a result of having to cope with
these highly, highly energy-rich habitats. But yes, one thing is that we're kind of putting to bed
is an old idea that a lot of these river fishes are very widespread, so something that can be found
near Lake Tanganyika, for example, thousands of kilometres away from my study site, was thought to
be the same thing as is found in the Lower Congo. But we're finding time and time again that these
so-called supposedly widespread species, when you actually look more closely we find that they're
not the same thing. There is much, much more localisation of fish populations than people had
previously thought. So that's one thing that's interesting.

The other thing that's kind of interesting but this is very specialised knowledge about African
river systems, but it looks as if quite a lot of the closest relatives of the fish that we're
finding in the Lower Congo are not found up in the main stream of the Congo as it rises up like
a...Joseph Conrad described the Congo as a snake with its head in the Atlantic and its huge body
curled up around the centre of Africa. So it's not on that huge backbone of Conrad's snake, we're
finding relationships actually with the Kasai, and the Kasai is a big southern tributary of the
Congo which actually reaches down and shares headwaters with the Zambezi. So we're beginning to
maybe get some inkling through looking at the fish about the deep geological history of Africa's

Robyn Williams: Any of the local people helping you in the way that they say, 'well, here's one we
caught last week and you probably haven't seen it before but we find it over there if you're very
lucky we haven't seen it more than once every five years'?

Melanie Stiassny: We rely very, very heavily on local knowledge. Fish is such an important source
of food, so people know fish, and villages have their prize fishermen and everyone has knowledge of
the local fish that are inhabiting the rivers they ply. So yes, we absolutely rely on fishermen, we
rely on our Congolese academic counterparts also and their students. And one of our big findings
that we really nailed last year on our last field season was we were able to show that the Lower
Congo is absolutely, hands down, the deepest river in the world. We found places in the Lower's not uniformly deep but there are huge underwater canyons that we've been able to
reveal using some pretty sophisticated Doppler equipment. And it's very interesting that the local
people kind of knew about these deep places. They didn't really know how deep they were, but
fishermen from villages a long way away are expending a lot of energy and a lot of time to come
downriver in their pirogues to certain places because those certain places apparently are very rich
in fishes. And what we've found is that those places very often correspond to these massively deep
canyons. I'm talking about canyons that are as deep as canyons in the ocean, deep, deep, deep, for
a river, unheard of deep.