Haemoglobin (Hb) is one of the most well-studied proteins to date and is key to blood oxygen (O₂) transport in nearly all vertebrates and some invertebrates, as it increases the total O₂ that can be transported in the blood and optimizes tissue O₂ delivery.

Teleost fishes represent over half of all extant vertebrates; they occupy nearly every body of water and in doing so, occupy a diverse array of environmental conditions. Scientists find their success is related to a unique oxygen (O₂) transport system involving their extremely pH-sensitive haemoglobin (Hb).

50-times better than humans

"Fish exploit a mechanism that is up to 50 times more effective in releasing oxygen to their tissues than that found in humans," says study lead author, Dr Jodie Rummer from the ARC 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."

Because of these adaptations, fish can live in all kinds of conditions, warm or cold water, and water with high or low oxygen levels. "This trait may be particularly central to performance in athletic species, such as long-distance swimming salmon or fast swimming tuna," adds co-author, Dr Colin Brauner from the University of British Columbia.