Receptive to change (Image: Jennifer Donelson)

Who knew fish were such expert flippers? One species at least can flip a bank of genes on and off to cope with warmer water within just two generations.

The new finding raises hope that ocean ecosystems could deal with rising sea temperatures, and even lead to adaptations that help fish farmers.


Many fish species suffer extreme consequences when their water temperature is raised by just a couple of degrees.

Their circulatory system’s ability to transport oxygen around the body can drop by half, meaning they cannot swim, grow or reproduce as effectively. This led to concerns that fish populations would shift their habitats or simply decline as the ocean warms this century.

Philip Munday from James Cook University in Townsville, Australia, and his colleagues showed in 2012 that one species of tropical fish affected by warmer waters – the spiny chromis damselfish – could completely adapt to 3 °C of warming over just two generations.

But how it happened remained a mystery until now.

Temperature test

To figure it out, Munday and his colleagues took wild fish and raised two new generations under tightly controlled conditions: some at the temperatures they naturally experience – averaging 23.2 °C to 28.5 °C – some at temperatures warmer than these averages by 1.5 °C or 3 °C.

They then measured their aerobic performance in the piscine equivalent of a treadmill – a cylindrical tank with a steady water current run through it. They also examined their full “transcriptome”: all the RNA produced by each gene in the fishes’ DNA, showing which genes were being used and which weren’t.

Fifty-three key genes were switched on or off after two generations of acclimatisation. The fish were ramping up the use of genes involved in energy metabolism and some involved in immune and stress responses.

Munday says the results strongly suggest that epigenetic changes in fish are passed on and strengthened in each generation.

It’s not evolution, because the experimental design ensured there was no selective breeding, but it’s possible that this sort of phenotypic plasticity helps drive evolution, says Munday.

This adaptability is good news for fish and is likely to happen in many fish species, says Munday.

The trade-off

“But there are no free lunches in this world,” he says. It is very likely that the acclimatisation to warmer seas comes at a cost to other functions in the fish. “Maybe we’ll see trade-offs with growth rates. In fact we have seen that fish that grow up in warmer conditions tend to be smaller.”

Munday says by figuring out the exact mechanisms behind the acclimatisation, those trade-offs can be understood and potentially even avoided by fish farmers.

“For example if you knew it was an energetic cost, you could supplement the feeding,” he says.

John Pandolfi from the University of Queensland says the results may have implications beyond fish.

“If fish can do this, why not other things?” he says. “This gives us some hope that adaptation and acclimatisation can go on at a rate that is keeping up with environmental change.”

Journal reference: Nature Climate Change, DOI: 10.1038/nclimate2724