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Temporary disguises let fish make sneak attacks 

But most of the disguises that scientists have known about so far, as in the butterfly case, are fairly long-term arrangements. Now, researchers are learning that some fish can masquerade as other fish temporarily, even flit between different disguises, to ambush various types of victims – both for food and sex.

Adoption of a particular disguise “seems to be linked to social context,” wrote Isabelle M. Côté and Karen L. Cheney of the University of East Anglia, U.K., in a paper published in the Jan. 20 issue of the research journal Nature. The pair studied the bluestriped fangblenny, a coral reef fish that has long been known to adopt a devious strategy to land a quick bite. 

The fangblenny disguises itself as a bluestreak cleaner wrasse, a type of small fish that makes a living by cleaning unwanted parasites off larger fish. Cleaner wrasse will even set up “cleaning stations” which larger fish can visit to be cleaned. The larger fish, apparently recognizing the usefulness of the wrasse, return the favor by not eating it.

The fangblennies exploit this. By adopting the wrasse’s appearance, they are allowed to get close to big fish. They then dart in, chomp off a mouthful of its flesh and take off. 

All this is well-known. But what what biologists didn’t know until now is that the fangblenny has another dirty trick, according to Côté and Cheney. It can turn off its cleaner fish-like appearance and become orange or brown, which lets it swim unrecognized among small schools of reef fish. These other fish, which are relatively harmless, unwittingly provide cover for the fangblenny, which darts out of the group to strike other victims at will. The fangblenny doesn’t mimic these other fish the way it mimics the cleaner wrasse, but evidently its coloration is good enough to let it blend in among them, according to the researchers.

In another paper in the same issue of the journal, Roger Hanlon of the Marine Biological Laboratory in Woods Hole, Mass., described a different type of temporary mimicry, that adopted by the giant Australian cuttlefish, Sepia apama.

Male cuttlefish guard their females fiercely, but nerdy male cuttlefish who haven’t got a lady have a trick to get to their competitor’s mates. They temporarily assume a feminine appearance in order to reach the female, and then successfully fertilize her. 

The disguised males “acquire the mottled skin patterning typical of females, and shape their arms to mimic the posture of egg-laying females, who are not receptive to mating,” the researchers wrote. 

This so-called sneak-guard behaviour by some animals was well-known before, but it wasn’t previously clear whether it results in fertilization by the “sneaker” male. The researchers said they settled the question by subjecting the laid eggs to DNA paternity testing, showing that the cross-dressing strategy works.

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