When we know someone is watching us, we behave differently. This ‘audience effect’ is something I have written about previously. However, a new study has found a type of audience effect never before found outside humans.

Just to recap, the ‘audience effect’ is any change in our behaviour caused by someone else watching. This evidently includes a wide range of possible changes. Top athletes have been known to perform as ineptly as novices when they have the pressure of an audience. However, the opposite can also be true: having a crowd cheer you on can make you achieve physical feats that you would not have alone.

Another interesting phenomenon in humans is how we change our behaviour based on what we want others to think of ourselves. You only have to click on a youtube video and see some of the comments people write to come to realisation that these individuals would not be nearly so rude if they were not hidden behind the shroud of anonymity. Whether you admit it or not, we all care about what others think of us to some degree. Psychologists call this our ‘image score’. In experiments done with people, they are less likely to behave selfishly if others are watching who could be judging them. However, until recently we had no idea that other animals were doing the same thing.

The cleaner fish is a fish that eats parasites off of other fish, so-called ‘clients’. Here is a video of a cleaner fish eating parasites off a moray eel (and coincidentally the first comment is also a good example of what I was talking about earlier – who knew that some are even provoked by eels being cleaned):

This arrangement between the cleaner and the client is a mutualism: it goes both ways. The cleaner fish obviously get an easy meal from their work, and the clients get rid of their parasites. However, it is a mutualism that would be very easy to disrupt. The clients could easily eat the cleaner fish if they so wanted. In return, the cleaner fish could ‘cheat’ and not actually eat the parasites, but instead eat a layer of mucus off of the clients, which they actually prefer to the parasites.

So, why might the cleaner fish not just cheat, and eat tasty mucus all the time? When the client feels that the cleaner fish is eating its mucus rather than the bugs on it, it gives a ‘jolt’: an involuntary twitch of its body. Other clients are often watching the cleaner fish at work, and may invite the cleaner fish to clean them next. They are able to judge how good a cleaner fish is by watching it clean other fish, and they will avoid the cleaner fish that make their clients jolt too often.

Through studying these interactions between cleaners and their clients, scientists have found that the cleaner fish actually change their behaviour when they know that another potential client is watching them cleaning. The cleaner fish seem to eat the mucus off of clients less frequently (measured as the client’s jolting rate) when there is another client watching. Thus they appear to be a better cleaner to new potential clients, and increase their chances of getting new clients in the future.

In the experiment, the cleaner fish changed their behaviour in the presence of the clients immediately, without any learning needed beforehand. However, since these were wild-caught fish, it is possible, or even probable, that this is something that they could have learned before they were caught for the experiment.

This is the first experiment showing a non-human animal behaving more cooperatively when it knows that others are watching it. From here, I think it would be interesting to know whether it matters who the client is, as has been shown to be the case for this species of livebearing fish.


Pinto, A., Oates, J., Grutter, A. & Bshary, R. (2011) Cleaner Wrasses Labroides dimidiatus Are More Cooperative in the Presence of an Audience. Current Biology.