Colourful Fish Mimics Identity Theft

Reef Dwelling Fangblenny Changes Colour to Hide among Other Fish

Mar 26, 2009

The blue-striped fangblenny fish can change its colouring to blend in with shoals of cleaner fish on coral reefs, hiding from predators while getting an easy meal.

The fangblenny lives on coral reefs throughout the Indo-Pacific, including Australia, Japan and the Red Sea. Australian marine biologists have observed it change its colour through several variations to mimic the different species of cleaner fish it hides among.

“Many fish can alter their colouration, but the fangblenny is the first example of a vertebrate that can change their colour at will to mimic a variety of different species,” said Dr Karen Cheney, from the University of Queensland’s School of Integrative Biology.

“The only other example is the mimic octopus that can alter its colouration and shape to resemble lionfish, flatfish and sea snakes.”

The fangblenny can change from its default colour of olive brown with two white stripes to at least six different variations or ‘identity thefts’, depending on what species they hide amongst. Body colours range from orange – olive – brown – black, and body stripes can change from neon royal blue – light blue – white.

“Most of the time two body stripes are seen, but in the case of the black body and neon blue stripes colour form (which is the mimic of the juvenile cleaner wrasse) the bottom stripe disappears to more accurately resemble the juvenile cleaner,” Dr Cheney said.

Fangblenny's Colour Vision Key to Mimicry

Dr Cheney said it was likely the fish has colour vision, unlike other marine animals, such as cephalopods, which are colour blind.

It has three different types of cone photoreceptors with different spectral sensitivities in its retina. For colour vision, animals need at least two.

“Fangblennies should be capable of discriminating between the various colour morphs they adopt and the colours of the fish they associate with,” she said.

Safe from Predators, Fangblennies are Able to Feed

The fangblenny’s mimicry is probably a combination of protective colouration and aggressive mimicry to get food. Generally solitary, it hides among shoals of cleaner fish, which carefully pick lice and other parasites off reef fish. Because it resembles these useful cleaners, it is unlikely to be spotted by larger fish which would normally attack it.

Safe among the cleaners, it can take the opportunity to do a little grazing on the client fish.

“The fangblenny mimics juvenile cleaner fish, but instead of removing ectoparasites from reef fish, they attack passing reef fish to nip at scales and fins,” Dr Cheney said.

Fangblenny Mimics Don’t Attack their Cover

One reason the blue-striped fangblenny is so successful at its mimicry is that it doesn’t attack its cover – the cleaner fish around it. In fact, although the cleaners are probably aware it is not one of them, they tolerate it.

“The cleaner fish tend to ignore the fangblenny when it is around,” Dr Cheney said. “Occasionally, cleaners have been observed to clean the fangblenny, which is surprising.”

Safe in its cover, the fangblenny does not aggressively attack the client fish, but instead just takes sly nips at their fins and scales.

“The fangblennies do not attack fish that visit cleaning stations, which probably helps to maintain the relationship between cleaner and mimic,” Dr Cheney said.

“If they did attack fish being cleaned, I am sure that cleaner wrasse would be more aggressive towards them and chase them away from their territory.”

Fangblenny Disguise only Good at a Distance

This careful behaviour ensures that predators don’t notice the fangblenny, which despite its protective colouration, could be distinguished on closer observation.

“Seen closely, they are not very accurate mimics of the cleaner wrasse,“ Dr Cheney said. “They swim very differently and their body shape is also slightly different. From a distance though, their resemblance is obviously sufficient to go undetected by passing reef fish.”

The copyright of the article Colourful Fish Mimics Identity Theft in Marine Life is owned by Sue Cartledge. Permission to republish Colourful Fish Mimics Identity Theft in print or online must be granted by the author in writing.