Movie: Dr Jeff Leis

Dr Jeff Leis, Australian Museum Senior Fellow, talks about how his work and how it relates to Biodiversity.

© Australian Museum
David Rawlinson
Dr Jeff Leis
David Rawlinson


I’m Jeff Leis. I’m a research scientist here at the Australian Museum and I work on fishes.

In Australia, we have about 5,000 different kinds – different species – of fish. They live in environments ranging from right up there at Cape York, up in the tropics and coral reefs, down into the quite cool waters in southern Australia and Tasmania.

They live in all kinds of marine habitats and they constitute about 75% of all the species of vertebrates in Australia.

The number of fish in Australia is much higher than many other countries – about three or four times as high as all the different kinds of fish in Europe, for example.

Not only does Australia have an extremely high biodiversity of fish, but within the life histories of those fish, particularly in marine fish, there are  larval stages – larval stages that look very different from the adults, that live in different places, that do different things, that eat different things, and, in effect, operate almost as a different species to the adults.

Now, this happens because when marine fish spawn, they generally do not look after their young after they’re spawned. The young are pitched off  the reef, for example, if the fish lives in a coral reef, out into the open water for two or three months –  two or three weeks to two or three months – and, at the end of that time, after they’ve survived all the problems that a little fish can face, including lots of big mouth out there who’d like to eat  them, they’re entirely on their own.

They have to find just the right kind of habitat at the end of that larval phase so they can complete their life cycle. It may be a juvenile nursery, which is different from where the adults live. It may be back on the reef where they started from. So, within marine fish and many other marine animals – many of the crabs and molluscs, for example – we have complex life histories, we have a chain of habitats that are required for the completion of the life cycle, we have a chain of different larval stages, morphologies, so we have biodiversity in many levels.

We have lots of different species, and within species, we have these different life history stages, which require different kinds of foods, different kinds of places to live. But, ultimately, the idea is to complete the life cycle using this chain of habitats, and if any link in that chain is broken, the life cycle can’t be completed and we lose that species.

We’ve got, in Australia, ranging from the world’s smallest fish, the stout infant fish, which is mature at only about 9mm and lives up in the coral reefs, to the largest fishes – the whale shark – all living in Australian waters.

So, there’s a tremendous diversity in whatever characteristic you care to think about in the kinds of fish that we have here in Australia. Some of these very small ones may seem insignificant, but just a good example – the cleaner fish that lives on the coral reefs is just a small little wrasse. You’d hardly notice it at all, except you do notice all the big fish that are queuing up outside the hole in the reef where it lives, because this cleaner fish actually cleans all the parasites off the bigger fish and helps keep them healthy, helps them survive, so we can look at them when we go diving or maybe even try to catch them with our line hanging off the end of a boat.

So, there are many interactions that go on at many different kinds of levels – not only the fairly obvious ones of a big fish eating a smaller fish, but also at different times of the life history, the species that the adult eats may actually eat the young of that adult when they are in the small larval stage. So, there’s sort of circles within circles.

And that’s what makes the study of fish in Australia so interesting.

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