Honest signalling allows the dental hygienists of the sea to get a snack, while avoiding becoming a snack


Cleaner shrimp gather at ‘cleaning stations’, within tropical coral reefs. Here, they remove and eat parasites from the mouths, scales, and gills of reef fish, known as their ‘clients’. The shrimp benefits from securing a meal, and the client benefits from parasite removal. However, many of these client fish species eat crustaceans like the cleaner shrimp. Therefore, signalling between the species likely exists. This is so cleaner shrimp can avoid being eaten and clients can avoid refusal to be cleaned. These signals must provide each species with reliable information about what the other is likely to do next. For this cleaning system to have evolved, each species must also be able to identify the signal sent to them, using their senses. However, both species view the world very differently. Cleaner shrimp see in black and white with low detail, whereas reef fish have sharper colour vision similar to humans.


The researchers observed interactions between cleaner shrimp and their clients at cleaning stations. They observed which behaviours commonly followed one another, to identify signals used by both species. Cleaner shrimp usually whipped their antennae to start the cleaning process. Clients often followed this by ‘posing’ in front of the station, ready to be cleaned. Shrimp regularly cleaned clients in these sequences. This suggests that antennae whipping signals a shrimp’s intention to clean. In the absence of antennae whipping, client fish often changed to a darker colour. This greatly increased their chances of being cleaned. This indicates that the darker colouration signals a request to be cleaned. Next, the researchers showed cleaner shrimp light and dark shapes on an iPad. Shrimp tried to clean the dark shapes more frequently, confirming that they can identify client’s colour change as a signal. Therefore, the researchers concluded that both antennae whipping and colour change function as signals, communicating the ability to provide a shared benefit.


These results provide evidence that both cleaner shrimp and clients can initiate cleaning interactions. This gives a further understanding to how these interactions have evolved, between species that could potentially be predator and prey. This study also shows how signalling has evolved between species with different vision. It is likely that cleaner shrimp are unable to see antennae whipping in fellow shrimp. However, this study demonstrates if the receiver can identify the signal, it is unimportant whether the sender has the ability to detect it themselves. Author of entry: Yavanna Burnham


Behavioural ecology

Subject Group

Zoology and Ecology






Posted by


on Mon Feb 22 2021

Article ID


Details of original research article:

Caves EM, Green PA, Johnsen Sn. Mutual visual signalling between the cleaner shrimp Ancylomenes pedersoni and its client fish. Proceedings of the Royal Society B: Biological Sciences. 2018;285:20180800.


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