Call them the Bonnie and Clyde of crustaceans. Put three or four cleaner shrimp (Lysmata amboinensis) in a tank together and after a month only two will remain, the survivors having killed the others off during the night. According to a study published today in Frontiers in Zoology, the shrimpicide happens because the crustaceans—which feed on fish parasites and dead skin cells near coral reefs in the Indo-Pacific region and the Red Sea—grow slowly if there's too many of them in a tank. The more shrimp, the less likely they are to molt, as molting makes them more vulnerable to attack. By killing off the others, a mating pair frees itself up to molt—and thus grow—as frequently as possible. And in shrimp, larger body size means more eggs laid, and a higher number of offspring. Who may then grow up to do some killing of their own.
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