Animal mimicry can become ineffective if it is used too often, and these canny fish know it.

In the world of Marine Biology, fish mimicry is a common form of deception, whereby mimic fish change colour to imitate other model species. This change can protect mimic species by deceiving predators, although can be ineffective if used too frequently or in the wrong context. Mimics reap the greatest reward when they are rarer than their models, leading receiver species (the targets of this deception) to become more aware of the mimicry itself.

One way around this is for mimic species to imitate various model species imperfectly; to act as an almost complete picture of several model fish rather than a complete picture of just one. This mouldable mimicry, or phenotypic plasticity, enables mimics to deceive target species by using multiple facades.

Fabio Cortesi and other researchers studied the species Pseudochromis fuscus, or dusty dottyback on the Australian Museum’s Lizard Island Research Station. He observed the mimicry of both brown and yellow dottybacks, and their interactions with the brown and yellow strains of the damselfish, the model species.

Cortesi established artificial reefs made of either coral rubble (a brown colour) or live coral (yellow), and filled each with either brown or yellow damselfish. He then introduced either a brown or yellow dottyback. After two weeks, he found that brown dottybacks on reefs with yellow damselfish had turned yellow, and vice-versa. Given this change occurred regardless of habitat, it was apparent that the colour of the damselfish was driving the change.

To firmly establish that dottybacks were changing colour to resemble adult damselfish, Cortesi stocked tanks with adult and juvenile damselfish of both colours, as well as a yellow or brown dottyback. By counting the number of surviving juvenile damselfish after 24 hours, it was clear that dottybacks of the same colour as adult damselfish were more effective at catching juveniles than dottybacks of mismatched colour.

To further test their hypothesis, an adult dottyback was placed in a tank with one brown and one yellow juvenile damselfish. Once again, the dottyback would more frequently catch the damselfish the same colour as itself, suggesting that young damselfish lower their defences when dottybacks closely resemble adults of their own species.

Given the clear purpose of the dottyback colour change was to lure juvenile damselfish by mimicking adult ones, Cortesi investigated whether there were even further benefits to this deception. Pictures of yellow or brown dottybacks were put up in front of either coral rubble or live coral backgrounds, and were calibrated to match the visual system of the coral trout-a predator to both dottybacks and damselfish. Using these and other control images, Cortesi tested whether the dottyback’s colouration also helped them avoid predation. Dottybacks in their usual habitat (that of the same colour as itself) were less vulnerable to coral trout attacks than those whose colour was mismatched.

Alex Vail, who grew up on Lizard Island, produced this video outlining Cortesi’s work and capturing phenotypic plasticity at work:

Fabio Cortesi is currently undertaking his PhD in the mimicry systems of coral reef fish for the University of Queensland, and has completed Bachelor degrees in Marine Biology at both UQ and The University of Basel, Switzerland. His work on the mimicry systems of coral reef fish has recently been published in the esteemed scientific journal, Cell Biology.