Bluestreak cleaner wrasses servicing a “client.”
Our legal system was built on the idea that different crimes warrant different punishments. Aggravated assault will snag you less jail time then, say, premeditated murder. And with no small degree of hubris, many of us believe that we’re the only animals on the planet to implement such a discerning system. But scientists have now learned that a species of fish also punish delinquents according to the severity of their crimes.
Starting life as females, bluestreak cleaner wrasse band together to clean off parasites and dead tissue from bigger fish, including sharks. At some point, the largest wrasse in a group, which typically has about 16 members, will change sex, become harem master, and reproduce with the others.
Yet while they normally feed on parasites, wrasse females actually prefer something a bit tastier: their clients’ mucus. However, a misplaced mucus nibble can annoy the client and thereby drive off the group’s food source, so males chase and bite any females caught misbehaving. Last year, scientists saw that punished females seem to fall back in line.