Are fish the greatest athletes on the planet?

Sydney: When you think of the world's greatest athletes, names like Usain Bolt generally spring to mind, but scientists have discovered the best athletes could well be found in the water, covered in scales, according to a new study.

The scientists discovered that fish are far more effective at delivering oxygen throughout their body than almost any other animal, giving them the athletic edge over other species.

"Fish exploit a mechanism that is up to 50 times more effective in releasing oxygen to their tissues than that found in humans," said study lead author Jodie Rummer from the Australian Research Council's Centre of Excellence for Coral Reef Studies at James Cook University.

"This is because their haemoglobin, the protein in blood that transports oxygen, is more sensitive to changes in pH than ours and more than the haemoglobins in other animals," Rummer noted.

This is especially important for fish during times of stress, to escape from predators, or when they are living in water that is low in oxygen. They can double or even triple oxygen delivery to their tissues during these critical times.

For the past decade researchers have been using rainbow trout to investigate oxygen delivery in fish. They first discovered and tested this mechanism by monitoring muscle oxygen levels in real-time in trout.

Now they have determined just how powerful that system can be and have compared the results with medical studies on humans.