Now here’s a case of you eat what you are

Now here’s a case of you eat what you are – cannibalism in mosquito fish

Sarah Boxer


Callous though it sounds, ”one way of satisfying nutritional requirements is to consume a conspecific,” to cannibalize. After all, such a meal ”comes ‘prepackaged,’ possibly with proper proportions of the materials necessary for growth, maintenance, and reproduction.” So write Gary Meffe, an ecologist at the Savannah River Ecology Laboratory in Aiken, S.C., and Martha Crump, a zoologist at the University of Florida, in the American Naturalist.

To check their hypothesis, they conducted experiments on eight groups of female mosquito fish, Gambusia affinis. (They chose the females of this species because they’re larger and cannibalize more often than the males.) Two control groups were fed a diet of commercial fish food containing fish meal, shrimp meal, cod-liver meal, and various plant products. The other six groups were fed the control diet plus one of the following: catfish muscle, bluegill muscle, frozen shrimp, mosquito larvae, or pulverized mosquito fish. The mosquito fish that ate mosquito fish gained more weight and reproduced more successfully than the rest.

Casual cannibalism — which comes of eating whatever happens to swim by, as mosquito fish do — is an evolutionary paradox. By cannibalizing, says Meffe, you run the risk ”that you’re going to eat your own offspring, which is costly because you’ve invested so much energy in reproduction. But if cannibalism were really so costly, you’d expect it would be selected against.” Yet it isn’t.

That means there must be advantages to cannibalism, at least formosquito fish, that outweigh the disadvantages of eating your offspring. Meffe and Crump think they’ve found one. ”Our study shows that there’s a nutritional advantage to cannibalism that partially negates the cost,” says Meffe. However, he’s quick to add, ”we’re not touting cannibalism.”

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