World’s largest treadmill…for fish

The new megaflume - a treadmill for large sharks

Measuring how much energy animal’s use for their daily activities can be REALLY useful. It can give us an idea of how much food they need to eat; how long they might be able to spend running or swimming at high speeds; and it can even help us understand why animals can live in one habitat, but not in others. We usually talk about an animal’s rate of energy expenditure in terms of “metabolic rate”, and scientists have come up with lots of cool ways of measuring metabolic rate at different levels of animal activity, e.g. resting, running, hopping or swimming.

Sharks are now giving land-lubbers a

run for their money. Image: Wikipedia

For land animals, pimped-up versions of treadmills (like we see in the gym) are pretty standard. The subject walks or runs at a range of different speeds, and the rate at which they consume oxygen (or produce carbon dioxide) is measured to determine metabolic rate. For animals that live in water, we use a pretty similar method, albeit with a few important differences.

A “swim-tunnel respirometer” is basically a treadmill for fish. At the most basic level, swim-tunnel respirometers are near-circular, sealed chambers in which water circulates at different speeds in order to encourage a fish (or other water-breathing animal) to exercise at different levels. Much in the same way as for treadmills, scientists then measure how much oxygen the fish consumes from the water inside the respirometer to estimate metabolic rate.

Testing the  metabolic rate of fish
is a bit different tothat of land animals
- just add water.
Image source here

Swim-tunnel respirometers have a pretty long history (at least 50 years or so), and are quite commonplace these days for fish physiologists all over the world. As you can imagine, building a device in which you have fast-flowing water, at controlled speeds, in a sealed container, that houses live fish, comes with a few logistical (and $$$) challenges. As a result, swim-tunnel respirometers have been restricted in size such that they could only accommodate fish up to about 10 kg. This means that we have relied on a fair bit of guesswork when it comes to metabolic rates of larger fish and sharks.

That is, until now. Recently we (a team from the National Institute of Polar Research in Japan, Uni of Adelaide, Uni of Tasmania and James Cook Uni) built and tested a huge swim-tunnel respirometer that holds around 26 tonnes of water, and that can be used with fish and sharks at least 100 kg body mass. We tested this “mega-flume” with a 2.1m zebra shark Stegostoma fasciatum swimming at 40 cm/s, and it worked really well - we compared our data to measurements from other sharks swimming around in tanks, and our results matched quite well. 

We are now planning to use the mega-flume with lots of other big sharks and fish – there is hardly any data on metabolic rates of these animals, so much of the information we can get from this new device will be pretty new and exciting. If you are interested in hearing more about the mega-flume or are interested in collaborating with us, please send me an email at n.payne@unsw.edu.au. More details can be found in our recent paper here.

A leopard shark, Stegostoma fasciatum, tests out the
new 26 tonne-water-capacity flume

Testing the mega flume north of Cairns, Australia