Fish are shrinking around the world. Here’s why scientists are worried.
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With billions of people depending on seafood for protein, determining the answer has big implications.

The pair restarted their work in Massachusetts with about 400 brook trout reared for up to eight months in tanks. The scientists kept some of the fish in waters set at 59 degrees Fahrenheit while others at 68 degrees Fahrenheit. All were fed the same diet.

By the end of the experiment, the difference was stark. The trout raised in warmer waters were on average less than half the size as the other fish.