Australasian Science: Australia's authority on science since 1938

From Cleaning Fish to Cleaner Fish

By Stephen Luntz

Dr Alexandra Grutter has revealed the extraordinary importance of cleaner fish.

Few scientists get children’s books written about them, but Dr Lexa Grutter is an exception. Having grown up cleaning the fish her father caught, she went on to transform our knowledge of the role of cleaner fish on coral reefs. Author Sneed Collard turned her work into a picture book, On the Coral Reefs, as part of a series on the biological sciences in which Collard puts the scientists at the centre of the story.

Grutter says she was always interested in science, having a shelf for her collection of rocks, shells and birds nests – with more under the house. Her father was a fisherman in Alaska (although the family wisely spent their winters in Mexico). “As the oldest child I spent a lot of time cleaning fish, often stopping to examine their gut’s contents,” she says.

Grutter applied to study at the University of Queensland, but was discouraged by visa restrictions. Instead she studied marine biology at a community college in Hawaii and worked for several years as a scuba diving guide. She says: “I used to take the tourists to see the cleaner fish stations”.

From Hawaii, Grutter went to the University of California Santa Barbara, where students sometimes carried surfboards even while riding bikes. While tempted to return to Hawaii for her doctorate, Grutter decided to fulfill her lifelong ambition of coming to Australia and went to James Cook University, where she spent 1000 hours scuba diving off Lizard Island for her thesis on cleaner fish and parasites.

Eventually Grutter landed at the University of Queensland after all. In the early 2000s Grutter’s work probably took up more of Australasian Science than any other researcher.

Had Grutter gone back to Hawaii her research might have been quite different. The indigenous cleaner fish there eat mostly mucus from their client fish. Since the mucus protects against bacteria and acts as sunscreen, client fish dislike losing it, which creates a puzzle as to why they tolerate cleaners. “The theory was that cleaner fish were parasites that took advantage of the clients’ hedonistic pleasure in tactile touching,” says Grutter.

However, when Grutter dissected Australian cleaners she told her supervisor: “They’re full of parasites”. In Australia, at least, cleaner fish provide an essential service, eating parasites that have become attached to their client fish.

Grutter’s long-term project studies coral reefs where cleaner fish have been removed. Every 3 months her team removes all the cleaner fish from seven reefs that range in size from a single room to an entire house. Within 18 months they observed that the abundance of mobile fish on these reefs was one-quarter of the number on the control reefs, with half the species diversity.

The effects on fish that spend their lives on a single reef took longer to detect, but after 13 years these are also more rare, smaller, and more parasite-infested. However, Grutter says little is known about the age at which fish die or flee uncleaned reefs. Remarkably, cleaner fish themselves seem reluctant to settle on reefs without existing cleaner fish after their period in the open ocean, potentially creating a feedback mechanism.

Grutter considers her greatest discoveries to be that “a single cleaner fish can eat 1200 parasites a day” (AS, June 1999, p.9) and “just how often a single fish will visit a cleaning station”. For rabbit fish this turns out to be once every 5 minutes – astonishing since they need to swim some distance to and from their patch of reef to the cleaner’s station.

Remarkably, however, one of Grutter’s collaborators recently found that the tactile touching theory has some basis after all. “The gentle stroking from the cleaner fish’s fins lowers the levels of stress hormones in clients,” says Grutter, who also found that cleaner fish prefer mucus but are deterred from cheating both by the client’s reaction and that of their fellow cleaners (AS, September 2011, p.12).

Fish can only get “sunscreens” via their diet, and cleaner fish have one of the best sunscreens of all reef fish. This might be because they eat mucus from so many different fish, and might also be one of the reasons they are so interested in eating it. But as a Hawaiian colleague said once: “It snot all that easy to work on!”

On the Coral Reefs arose when Collard visited Lizard Island to research a book. He interviewed Grutter, among other scientists, and decided she was so interesting that she deserved a book of her own. She says: “I don’t get people stopping me in the street, but I have had children write to me from around the world”.