Zegni Triki spent three months in 2018 collecting data at Lizard Island Research Station for her PhD. Her work was supported by a 2018 Lizard Island Doctoral Fellowship. One part of Zegni’s research examined changes in the brain complexity of cleanerfish, specifically the Common Cleanerfish (Labroides dimidiatus).

Life is complex for Common Cleanerfish. They have a specialised diet consisting of the crustacean parasites on the skins of other reef fishes and fish-skin mucus. They swim close to the surface of the host fish and pick the parasites off with their specially developed mouthparts.

A pair of adult Labroides dimidiatus cleaning a Parrotfish Scarus frenatus © Andy Lewis


Life is complex because Common Cleanerfish compete to attract the biggest fish with the most parasites to their “cleaning stations”. In a healthy reef community, there are many cleanerfish operating cleaning stations in close proximity to each other. Attracting the big fishes is a challenge because big fishes are mobile enough to be picky about the station where they get cleaned. Which station gets chosen depends on the quality of service being delivered. Is the service quick? Does the cleaning operation look like a standard once-over or is it the works, with a full buff and polish at the end?

In reefs where there are many cleaning stations, Common Cleanerfish have to set themselves apart from the others and they do so by doing more showy and demanding cleaning when high-value fish are nearby. Common Cleanerfish also recognise those fish that are mobile enough to be able to swim off to other cleaning stations and give them priority service, cleaning them before attending to the needs of the locals.

To manage customers well and to put on a great show of cleaning at just the right times takes sophistication. It turns out that some Common Cleanerfish are smarter and they tend to run more attractive cleaning stations.

Juvenile Common Cleanerfish

Juvenile Common Cleanerfish (Labroides dimidiatus) attending to a Giant Moray (Gymnothorax javanicus) © Andy Lewis


The cyclones and the two bleaching events that have affecting reefs around Lizard Island in recent years have been accompanied by an 80% reduction in the density of Common Cleanerfish around Lizard Island. While densities of fish requiring cleaning have also declined, they have not declined by such a large percentage. Zegni found that this environmental change, reducing competition between Common Cleanerfish, also appears to have reduced the sophistication of their customer management strategies. Running a slick operation takes more effort and if the extra effort is not required, the Common Cleanerfish simplify their services.

The research involved analysis of the strategic complexity employed by forty specimens studied in the Lizard Island Research Station aquariums. This behavioural analysis was augmented with detailed analysis of brain size and complexity for twenty individuals selected from those original forty specimens.

In the aquarium environment, Zegni found significant variation in brain complexity between the individual fish. She also found that brain complexity is influenced by the environment and life experiences as the fish develops into a mature adult. Fishes that mature in low-competition environments need less sophisticated strategies to attract a good feed and so tend to develop less complex brains.

As fish populations gradually recover from the cyclone and bleaching events of recent years, it will be interesting to observe how the competition between cleaning stations steps up. It will also be interesting to see how the health of the reef fish improves as cleaning services become more readily available and parasite loads decline. It will be great to have Zegni continuing her research at Lizard Island again this year.

Geoff Shuetrim, LIRRF Trustee