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'Dancing' fish could be key to ridding salmon farms of parasites

Biologists study the social behavior of fish through their communication, which includes and . Cleaner fish feed on the parasites that live on the skin of many different species of fish, known as clients.

Some species of tropical cleaner fish are skilled communicators and display . focusing on the social behavior of cold-water cleaner fish aims to help salmon farmers control parasitic sea-lice in aquaculture.

Dancing tropical fish

Diving among the coral reefs of the Indo-Pacific—the geographic region comprising the Indian Ocean and the west Pacific Ocean—you might see a , which is a species and perhaps the first fish to . This wrasse relies on cleaning parasites from clients to find the majority of its diet.

Attracting new clients and getting them to cooperate while removing parasites can be a . To make the job easier, bluestreak cleaner wrasse perform a and massage clients with their fins. This display , allowing the cleaner to approach and closely inspect its skin for parasites.

This is an because both parties benefit from interaction: the cleaner gets a meal and the client is rid of parasites. For decades, biologists have studied the behavior of bluestreak cleaner wrasse to research mutualism, however, there are of cleaner fish which are yet to be studied.

Cold-water communication

Investigating whether cold-water cleaner fish communicate with clients is particularly important for the salmon aquaculture business. Sea-lice are a huge , and problem for salmon farmers, and controlling louse populations is a big challenge.

may help reduce parasite numbers on the salmon. However it is unknown whether cold-water cleaner fish dance for their clients, or whether these species can communicate at all, which would affect from salmon.

To investigate this potential, our at the University of Guelph looked at how cunner wrasse communicated with salmon.

Strike a pose

We filmed , a native cleaner fish from eastern Canada, swimming inside aquariums with salmon to see how the two species interact. At first, we were disappointed not to see any underwater dancing, but then a particularly large cunner swam out in front of the salmon and made an unusual pose.

The cunner pointed down towards the floor, spread its fins open wide, and hung suspended in the water for a few brief moments before swimming away. Several minutes later it returned to strike another pose, this time for longer, and moving slowly around the salmon.

Our video analysis showed that cunners posed more frequently towards salmon that had sea-lice on their skin, compared to salmon free of parasites. Cunners that posed more frequently would get closer to salmon, and also spend longer time periods visually inspecting the salmon.

These results imply that cunner wrasse pose towards salmon as a form of communication, which helps the cunner gain access to lice on the salmon's skin.

Poser for mutualism

Cunner wrasse didn't perform the complex ballet of their tropical counterpart, however, they displayed a series of highly exaggerated poses that was reminiscent of the of the late 1980s.

This simpler dance style might reflect the fact that cunners can find , and don't rely on eating parasites as much as bluestreak cleaner wrasse. Studying more diverse species of cleaner fish might give more insight on the biology of mutualism and fish communication.

It's important to note than not every cunner showed posing behavior and some individuals would hide from salmon, whereas others embraced the spotlight. Measuring differences in posing behaviors could help farmers choose the best cleaners to use for sea-lice control. It could also help identify factors that influence communication between cunner wrasse and salmon, like and .