project news

Fish spa on Mafia Island

News item submitted by Frontier
News item dated 8 Sep 2009


In the crystal east coast waters of Mafia Island, Frontier’s Tanzania Marine Research Team are carrying out a groundbreaking study into a shark's best friend: cleaner wrasse.

Known as obligate cleaners, cleaner wrasse operate ‘oceans spas’ in their coral reef communities. They set up well-defined, permanent cleaning stations, which 'client' fish visit to have their parasites removed.  

Much research has focused on the relationship between cleaner fish and their clients, but little is known about how they choose their cleaning stations and what makes a desirable site. Our new research is therefore geared towards investigating the relationship between coral reef structure and client/cleaner interactions.

The team are studying which species use the cleaning stations and the costs and benefits of cleaning. The work will improve our understanding of the importance of cleaner wrasse and their spa stations for coral reef biodiversity.

Many fish live their entire lives on reefs, finding food and protection within the holes and crevices formed between corals. The huge numbers of organisms which live around reefs result in many unique and interesting relationships being played out beneath the waves. The bond between small cleaner fish and their massively larger clients is no exception – even sharks enjoy their attentions, recognising their striped bodies and sinuous movements as a signal not to attack.

It is well in the sharks’ – and most other fishes’ – interests to allow cleaner fish to do their job. One of the many hardships faced by reef fish is how to remove ever present parasites that cling to their bodies. If these ‘ectoparasites’ are not removed they can lead to infection and even death, making it vital that fish seek assistance.

Permanent cleaning fish stations are formed when one or more cleaning wrasses set up a residence within the boundaries of a distinctive object such as a defined coral head. Fish laden with parasites form an orderly queue while the hard working cleaner wrasse move from fish to fish.

This is a perfect example of a mutualistic symbiotic relationship; cleaner fish obtain all their nutritional requirements from the parasites they remove, and the client fish become free of their parasite load.

Cleaner fish also have another strange trait. All cleaner wrasses start their lives as females. In a small group cleaner wrasses there will only ever be one male, the rest are females or juveniles. When the male dies, the strongest female changes its sex and takes over the dead male’s mantle - an occurrence known as sequential hermaphroditism.

Read more about our Tanzania Marine Project.