First Author

Altruistic behaviour, cooperation and deceit are not the most obvious concepts to associate with fish, but the work reported on page 975 explores these very characteristics in the piscine world. Redouan Bshary, a zoologist at the University of Neuchâtel in Switzerland, teamed up with Alexandra Grutter, a biologist at the University of Queensland in St Lucia, Australia, to study cleaner fish (Labroides dimidiatus) and their interactions with their ‘clients’. The cleaner fish eat parasites on the clients, but they sometimes ‘con’ the clients by eating their mucus instead. After spending hundreds of hours underwater observing the fish, Bshary and Grutter did controlled experiments in tanks. They found that both parties keep score of long- and short-term benefits to fine-tune their interactions. Bshary came up for air to talk to Nature about the work.

How much fun did you have at sea?

Lots! I sat in coral reefs about 2–5 metres deep, with the cleaner fish 2–3 metres away. There was always something going on. The clients want the cleaners to eat the parasites, but the cleaners want to eat the mucus. There is a conflict of interest, so the client has to make the cleaners want to clean them, by chasing them or biting them. Sometimes the cleaners cheat by eating mucus rather than parasites. To pacify their client, they give massages.

How did you replicate this in the lab?

In our experiments, we replaced the clients with plexiglass plates that are moved with a lever, so we could control how the ‘client’ responds. We put pieces of prawn on the plate in place of mucus, and fish flakes in place of the parasite. The cleaner fish like prawns and they don't like fish flakes. If the fish ate what they like — a piece of prawn — we took the plate out of the aquarium. So the cleaner fish learnt that eating their preference removes their food source.

What immediate effects did this have on your own dietary preferences?

After measuring prawn consumption for a month, you don't want to eat prawns. It took two months for me to eat prawns again.

Most humans don't like parasites or mucus, so how could this translate?

In humans, it is probably about giving (money or direct help) for prestige — you can even self-advertise your deeds. Americans say, ‘do something good, then talk about it’, so you get social or professional prestige.

Do you use these theories to manipulate people?

No — not consciously!