During a severe heat wave in 2023, scientists scuba diving off the coast of Papua New Guinea captured clownfish to measure their bodies. Between February and August, they calculated the length of 134 of these iconic, orange and white fish once a month, taking a total of six measurements for each fish.

Those measurements revealed something peculiar: Most of the fish shrank.

This week, the researchers reported their findings in Science Advances, concluding that the fish got shorter — on the scale of a few millimeters, or a small, single-digit percent of their length — in response to the heat wave.

“We were so surprised to see shrinking in these fish that, to be sure, we measured each fish individual repeatedly over a period of five months,” said Melissa Versteeg, a........

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