Mimicking its poisonous cousin the yellowtail fangblenny (Meiacanthus atrodorsalis), the bicolour fangblenny (Plagiotremus laudandus) escapes predation on coral reefs and can feed on other fish unharmed.
"This fish resembles another poisonous reef fish — the yellowtail fangblenny — to avoid predator attack and to also avoid detection from passing reef fish, which they approach and attack to gain a meal of skin and fins," said Australian marine biologist, Dr Karen Cheney from the University of Queensland’s School of Biological Sciences.
Cunning Mimic Gains Dual Benefits
Mimics are unrelated animals or plants that closely resemble another species to either avoid predation, capture prey or attract potential mates. The bicolour fangblenny seems to gain at least two benefits – protection and prey – which is unusual in mimicry.
"This is the first example of a mimicry system in which the mimic gains multiple benefits from its resemblance to another species," Dr Cheney said. “It is both a mimic in terms of increased access to food (aggressive mimicry) and reduced predation risk (Batesian mimicry).”
She has been studying the bicolour fangblenny and the fish it mimics and those it attacks on the coral reefs at Hoga Island, Indonesia, and at Lizard Island on the Great Barrier Reef, observing the number of attacks made by the mimic and how close it stayed to the fish it resembled.
Her paper, ‘Multiple selective pressures apply to a coral reef fish mimic: a case of Batesian–aggressive mimicry,’ was published in Proceedings of the Royal Society B on February 24.
Predators and Prey Can’t Tell Mimics from Model
The bicolour fangblennies gained access to more reef fish victims, which they attack to feed on fins and scales, when they spent more time associated with their model, the yellowtail fangblenny.
In other words, their potential meals thought they were poisonous, like the yellowtail, so they didn’t attack first, and were easy prey for the mimics. Bigger fish that would normally attack the bicolours also stayed away for the same reason.
To test how successful the bicolour fangblennies were at deceiving their predators and the reef fish they ate, Dr Cheney set up models of fangblennies in the water. The models were clear perspex shapes containing photos of bicolour fangblennies – exact replicas of the mimic fish. She also put in other replicas that were not so exact as controls.
“Exact replicas of P. laudandus incurred fewer approaches from potential predators compared with control replicas that varied in resemblance to P. laudandus,” Dr Cheney said. She said it was possible that the mimic used its colour, which is similar to that of the poisonous yellowtail, as a signal to warn potential predators not to attack.
Colour Important in Signaling Among Fish
Dr Cheney has studied other reef fish for whom colour is an important signalling tool, and as a means of duping other reef inhabitants. A recent study confirmed that cleaner wrasse, which remove parasites from passing reef fish, use their black and neon blue colouring to advertise their services and so avoid being attacked.
Another study by Dr Cheney showed another species of fangblenny, the blue-striped fangblenny, uses its ability to change its colouring to mimic juvenile cleaner wrasse and hide among shoals of the cleaner fish, safe from predators.
Unlike the blue-striped fangblenny, the bicolour fangblenny cannot change its colour to mimic its model, but has evolved to have colouring similar to the model. While it is not identical to the model, having more yellow and a smaller size than the poisonous fish, it has proved similar enough to deceive other fish at a distance.
For more on deceptive behaviours, you might also be interested to read Colourful Fish Mimics Identity Theft, Transvestite Lizards Imitate Females and Crayfish Cheat Their Opponents with Fake Claws.
Sue Cartledge - I'm a science, health, nutrition and lifestyle journalist, fascinated by the way the physical world operates in all its forms, and how ...
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