Meet the fish that hop, skip and jump

Friday, Aug 14, 2015, 04:03 AM | Source: Pursuit

Stephen Swearer

From the incredible flying fish whose modified pectoral fins allow it to glide up to 70km/h to a wriggling salmon jumping upstream – why do fish choose to leave water?

University of Melbourne fish ecologist Associate Professor Stephen Swearer gives us six reasons.

1. To avoid being lunch

It’s simple – so they won’t be eaten.

“I’ve been on marine research vessels and seen flying fish leap out of the water thinking we might be a big fish predator. They will often glide off at right angles to the boat with incredible speed and manoeuvrability,” says Associate Professor Swearer.

“They do this to get some distance on the predators but also so the predators can’t work out where they will land back in the water. In just a few seconds they can travel up to 50 metres.”

2. To eat lunch

“Another reason fish leap out of water is to capture prey. People may be familiar with trout leaping out of the water to feed on mayflies,” says Associate Professor Swearer.

“While it’s usually birds that dive into water to eat fish, there are some fish, like the arowana which live in the Amazon, that will dive into the air to eat birds.”

Arowana have been found with the remains of birds, bats and snakes as well as crustaceans and insects in their stomachs. They look a bit like Grumpy Cat with their downturned drawbridge mouth that would have no problems grabbing an unsuspecting bird.

3. To reinflate their internal buoyancy vests

“Most bony fish have swim bladders, which are these gas-filled sacs that help the fish control buoyancy in the water,” says Associate Professor Swearer. “It means they can stay at their current depth without having to waste energy swimming.

“The swim bladder progressively loses a little gas so to replenish their bladders, some species will periodically go up to the surface to gulp some air but others will leap to avoid being eaten by birds.”

4. To slap loose a pesky parasite

“There is also some evidence that fish may leap out of the water so they can slap down on the surface of the water to dislodge parasites,” says Associate Professor Swearer. “But more commonly they will take advantage of the services provided by cleaner fish or shrimp.”

5. It’s the only way to go up a waterfall

Fish may be trying to get around obstacles. You may have seen spectacular footage of salmon leaping up over small waterfalls. The easiest way to move past the pounding pressure of the waterfall is to go via the path of least resistance with minimal energy and effort – the air.

6. Some spaces just cramp their style

If you’ve ever kept fish in a tank you’ll know that the odd fish will make a leap for freedom. What motivates this behaviour? Was the tank décor not right? Was it the neighbours? Was it the fish or the owner?

“I spent a summer in high school as an intern at the Waikiki Aquarium in Hawaii,” says Associate Professor Swearer. “All of the tanks needed to be covered to prevent fish from trying to jump out and escape. Clearly being in a confined environment is not a natural situation for a fish. It does, however, make you realize just how aware fish are of their surroundings when in captivity and what risks they are willing to take.”

Associate Professor Swearer is working on several research projects, ranging from rare freshwater species in the Kimberley to salmon aquaculture in Norway.