Blue Planet II

Clownfish’s incredible show of strength

By Martin Poyntz-Roberts, Nicola Brown, Kara Segedin

In an incredible feat of strength and problem solving, saddleback clownfish (Amphiprion polymnus) have been filmed working together to move objects across the sea floor for the very first time.

This remarkable behaviour was captured on camera by the Blue Planet II crew and the footage is being utilised in a scientific study.

Cameraman Roger Munns
Cameraman Roger Munns. Credit: Roger Munns 2017
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“What was really cool about this sequence is that clownfish are such a well known animal that I hope the behaviour comes as a complete surprise” says cameraman Roger Munns.

“It really was amazing to see such a small fish move such a big object relative to its size,” he adds.

Like many species of clownfish, the saddleback lays its eggs on hard objects. While other clownfish find suitable locations (such as shells) on the seabed or reefs where they live, things aren’t quite so simple for the saddleback.

Saddlebacks make their home amongst the venomous tentacles of the ‘carpet anemone’ (Stichodactyla gigantea). Immune to their sting, it shelters them from predators, but also means they live out their lives in the open sand, away from the reef and its readily-available egg-laying surfaces. With no hard surfaces close by, the saddleback resort to using their initiative. Using all their strength they are able to push objects up to 10 times their own weight, it’s thought to a distance of two metres. An incredible feat for a tiny fish. Once home, they tuck the object under the safe haven of the carpet anemone.

Though they often select shells and rocks, the clownfish filmed for Blue Planet II shift a large coconut shell across the sand before laying their eggs on its surface.

A male saddleback clownfish pushes a coconut shell to its anemone in Borneo
A male saddleback clownfish uses all the strength it can muster to push a coconut shell to its anemone in Borneo. Credit: BBC 2017

Munns first heard about this remarkable behaviour from a photographer at a dive resort in Malaysian Borneo, but it wasn’t until Blue Planet II producer Jonathan Smith contacted him looking for stories, he remembered it.

“I was instantly convinced that it could be a perfect story for Blue Planet II,” says Smith.

“When Roger mentioned it we researched it and the only reference we could find was to a paper in the 1970s, but it was far from well documented in this paper and therefore it did not really shed much light on it. 

The team collaborated with Marine Biologist Dr Alex Vail who is now working with a team to publish a paper about the behaviour. In conjunction with filming, Vail has been able to document the types of objects being pushed – from coconut husks and empty shells to glass and plastic bottles: “From our experiments in Thailand, we found that they are actually very picky of what type of objects they prefer. We haven't fully analysed the results yet, but it seems like they prefer glass bottles of a colour that disguises their eggs better, objects that are heavy enough not to wash away, and with a nice clean surface to attach their eggs to,” says Vail.

“The data is currently in the analysis stage and we'll be publishing as soon as we're able to. The idea and the background knowledge for this study came completely from The Blue Planet II team's filming of the behaviour, so without this the scientific study would not have happened,” says Vail. 

#OurBluePlanet is a collaboration between BBC Earth and Alucia Productions.