Put a fish in a tank with unlimited food and it will gobble until it grows many times its size. This is possible because the fish has a much larger digestive system than it actually needs. But why spend so much energy maintaining all of these guts when fish in the wild don't eat nearly as much? A new analysis of 600 fish populations (including the bluegill, pictured), reported online today in Nature, suggests that large guts help fish deal with feast or famine conditions in the wild . A digestive system that's two or three times bigger than needed helps these fish gorge on food when they find it and store the calories for times when food is scarce. And, in the long run, that makes hauling around a bunch of guts worthwhile.
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