Wildlife & Wild Places

How “Walking” Fish Made the Leap From Ocean to Land

The Pacific leaping blenny (Alticus arnoldorum) is a fish out of water. The legless land fish makes its home on the intertidal rocks on the island of Guam (map), and new research shows how this strange fish was able to make the leap from stealthy swimmer to landlubber.

The two- to three-inch (four- to eight-centimeter) blenny does everything on land, from finding its steady diet of algae and detritus to mating and nesting. Its love of dry land is perhaps best reflected in how it escapes from threats like predators or researchers trying to trap it. (Related: “Pictures: ‘Walking’ Fish a Model of Evolution in Action.”)

Pacific leaping blenny (more pictures here). Photograph courtesy Courtney Morgans, UNSW

“They actually don’t retreat into the water. Instead, they hop across the rocks and try to hide in rock holes and crevices. Their body shape has changed just enough to make them poor swimmers, so it’s better for them to try and find a hiding place on land,” said Terry Ord, an ecologist at the University of New South Wales in Australia and co-author of the new study in Animal Behaviour.

One of the keys to the blenny’s success on land is camouflage: The fish’s brown, mottled skin blends in with the intertidal rocks, allowing it to escape predators like birds and crabs.

Animals can use a variety of techniques to keep from being eaten, but one of the most common is being invisible. In recent experiments, Ord and UNSW colleague Courtney Morgans compared the color of five different populations of blennies around Guam to the rocks on which they lived. In each case, the two colors were nearly identical, which was a strong hint that the blennies were blending in to the surrounding environment to hide from predators.

To test this hypothesis, Ord and Morgans constructed life-size clay models of blennies. They placed a bunch of these models either on the rocks (where they would blend in almost perfectly) or on a sandy beach (where their coloring would make them stand out).  (See “Two New ‘Walking’ Batfish Species Found.”)

After several days, the researchers collected the models and recorded how often the blennies had been attacked by lizards, birds, and crabs by counting the bite marks and other wounds in the clay. The more obvious models on the sand had significantly more bites than the models on the rocks.

Evolutionary Snapshot

Animals first left the oceans for dry land nearly 400 million years ago, at the end of the Devonian period. Understanding how animals made this move will provide tremendous insights into the evolution of life on land, Ord said.

But since only fossils remain of these pioneering life-forms, scientists can’t watch these animals in action. But they can study another species making a similar transition, the blennies, to learn how animals made the switch to land. (See pictures: “Nine Fish With ‘Hands’ Found to Be New Species.”)

“The blennies were probably reasonably well camouflaged when they first emerged from the water—at least enough to let them survive long enough to reproduce and adapt,” Ord said.

Besides camouflage, the blenny’s fish ancestor had to make some other major adaptations, like figuring out how to move on rocks instead of just swimming, and how to breathe air instead of getting oxygen from the water. (Related: “Fish Lives in Logs, Breathing Air, for Months at a Time.”)

Although Ord still isn’t sure exactly when the blennies began their move from sea to land, he knows it was later than the Devonian.

“These blennies provide an evolutionary snapshot of the colonization of land,” Ord said.

Follow Carrie Arnold on Twitter and Google+.

Carrie is a freelance science writer living in Virginia. When she's not writing about cool critters, she's spending time outside, drinking coffee, or knitting. You can visit her website at http://www.carriearnold.com
  • DAVID CAPETTINI

    I don’t understand. If these were the first animals that began to live on land, why would they need protection from predators? There weren’t any birds or lizards. The only predators would have been in the sea.

    • Carrie Arnold

      Hi David,

      Good question. You’re right- the first animals to leave the ocean would have been drawn to land in part because of the lack of predators. And this happened around 400 million years ago. I asked Ord when he thought the blennies began to move onto land, and he said he wasn’t sure, but that it was much, much after this (perhaps 10-50 million years ago or so, but don’t hold me to this. I’m just guessing). So when the blennies began moving to land, there were lots of predators there to snack on them, which would make camouflage very important. The main ones they are hiding from are lizards, birds, and crabs.

    • Carrie Arnold

      Hi David,

      Good question. You’re right- the first animals to leave the ocean would have been drawn to land in part because of the lack of predators. And this happened around 400 million years ago. I asked Ord when he thought the blennies began to move onto land, and he said he wasn’t sure, but that it was much, much after this (perhaps 10-50 million years ago or so, but don’t hold me to this. I’m just guessing). So when the blennies began moving to land, there were lots of predators there to snack on them, which would make camouflage very important. The main ones they are hiding from are lizards, birds, and crabs.

  • DAVID CAPETTINI

    I don’t understand. If these were the first animals that began to live on land, why would they need protection from predators? There weren’t any birds or lizards. The only predators would have been in the sea.

  • Eric Paul

    @David Capettini – this particular species was not the first animal to leave the ocean. This is the most recent example and studying it will give an insight into the evolutionary changes that were necessary for animals in Earth’s history to have accomplished the same. But yes, you are right – the first couple of species to move out of water probably didn’t need to worry about camouflage, or similar, when out of water.

  • Eric Paul

    @David Capettini – this particular species was not the first animal to leave the ocean. This is the most recent example and studying it will give an insight into the evolutionary changes that were necessary for animals in Earth’s history to have accomplished the same. But yes, you are right – the first couple of species to move out of water probably didn’t need to worry about camouflage, or similar, when out of water.

  • Tanamon Somchana

    There are many kind of animals live in the sea but sometime can go to the mud.

  • Tanamon Somchana

    There are many kind of animals live in the sea but sometime can go to the mud.

  • Gatot Nugroho Susanto

    Nice article. I research in Andamia too, I used Andamia heteroptera and i found that Andamia heteroptera have vertebrate structure similar with tetrapod. Andamia heteroptera has zygapophysis between their vertebrae.

    • Carrie Arnold

      Interesting! I wasn’t aware of some of their detailed anatomy- thanks for sharing.

    • Carrie Arnold

      Interesting! I wasn’t aware of some of their detailed anatomy- thanks for sharing.

  • Gatot Nugroho Susanto

    Nice article. I research in Andamia too, I used Andamia heteroptera and i found that Andamia heteroptera have vertebrate structure similar with tetrapod. Andamia heteroptera has zygapophysis between their vertebrae.

  • Tom Rutter

    I think they meant first vertebrate animals. Arthropods made the “leap” to land long before the end of the devonian. And probably evolved predators on land within that sub-group.

  • Tom Rutter

    I think they meant first vertebrate animals. Arthropods made the “leap” to land long before the end of the devonian. And probably evolved predators on land within that sub-group.

  • Sherry Bendickson

    This is the same area that gave us the oldest Human DMA. So this creature shouldn’t be a surprise. We should be doing more research in the area…on land and under water.

  • Sherry Bendickson

    This is the same area that gave us the oldest Human DMA. So this creature shouldn’t be a surprise. We should be doing more research in the area…on land and under water.

  • Makia Harris

    Wow they evolved and have learn how to adapt.♥

  • Makia Harris

    Wow they evolved and have learn how to adapt.♥

  • ahmed

    good friend national geographic

  • ahmed

    good friend national geographic

  • Aliyu Sanusi

    Hi Carrie and David,
    Carrie your explanation makes sense, but I would have rather thought that they needed the camouflage because they also lived in water with predictors. They needed to retain those features probably as predictors roam the land and skies.

  • Aliyu Sanusi

    Hi Carrie and David,
    Carrie your explanation makes sense, but I would have rather thought that they needed the camouflage because they also lived in water with predictors. They needed to retain those features probably as predictors roam the land and skies.

  • Hyder

    Is there any similar evolution going on in reverse , like the evolution of dinosaur transforming to whale …

  • Hyder

    Is there any similar evolution going on in reverse , like the evolution of dinosaur transforming to whale …

  • screenmachine

    Evolution and the “study of it” are pure conjecture and speculation and will continue to go nowhere.

  • screenmachine

    Evolution and the “study of it” are pure conjecture and speculation and will continue to go nowhere.

  • Ann McMaster

    To screenmachine. It is likely safe to say that you have not taken the time to read Darwin’s origin of the species. He describes the well accepted concept of artificial selection that we know resulted in the development of domesticated breeds of animals. He then applies that same principle to natural selection. Natural selection which results in a change in the traits of a population over time has been observed in several species. This is not speculation.

  • Ann McMaster

    To screenmachine. It is likely safe to say that you have not taken the time to read Darwin’s origin of the species. He describes the well accepted concept of artificial selection that we know resulted in the development of domesticated breeds of animals. He then applies that same principle to natural selection. Natural selection which results in a change in the traits of a population over time has been observed in several species. This is not speculation.

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