Putting function before form, members of the Perissodinus genus of fish have developed a hugely lopsided jaw that provides a distinct feeding advantage. Research published in the open access journal BMC Biology describes how these scale-eating fish, called cichlids, develop mouths directed either to the left or the right — enabling them to feed on the opposite side of their prey.
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There are other fish that show “handedness”. Anableps anableps, the four-eyed fish is a livebearer with a sexual organ that moves either to the right or to the left. Females have a corresponding organ that can receive only from the left or from the right. It takes all sorts.