Fang blenny is definitely a mimic

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The Fang blenny, Plagiotremus rhinorhynchos, a specialised predator which feeds on chunks of skin and fin from marine fish, has evolved mimetic colouration to enable it to mingle with groups of Cleaner wrasse, Labroides dimidiatus.

By looking like the Cleaner wrasse, a fish which performs a useful role on the reef by picking off parasites, the Fang blenny can get close enough to prey to take a bite out of them without arising their suspicions. However, this form of aggressive mimicry hasn't been studied experimentally in this fish extensively before.

In a new paper, published in the journal Oecologia, two biologists from James Cook University in Queensland, undertook an experiment with the two species to find out how the aggressive mimicry works in nature.

By studying fish in Kimbe Bay, Papua New Guinea, the scientists noted that the colour similarities only applied to small Fang blennies, as the colouration of adults was quite different to that of the Cleaner wrasse.

Although the two fish were found living together in some spots, the Fang blennies were only present when there were lots of juvenile Cleaner wrasse in the area.

And, when the two were found together, the Fang blennies hung around less than a metre from the wrasse - a much smaller distance than the two fish would normally be found apart.

To test whether the feeding success of the blennies was dependent on the presence of the Cleaner wrasse, the scientists caught most of the wrasse and removed them from the area to see what would happen.

Interestingly, when the wrasse were removed, the blennies colouration changed back to the non-mimetic form, which doesn't resemble the markings of the Cleaner wrasse. It also made the fish about 20% less likely to get an easy lunch, supporting the theory that the Fang blenny is indeed an aggressive mimic of the Cleaner wrasse.

For more details see: Moland E, Jones GP. (2004) - Experimental confirmation of aggressive mimicry by a coral reef fish. Oecologia. 2004 Jul 28.