Clownfish adapt their size to fit their environment

A recent study from Newcastle University reveals that clown anemonefish can literally adapt to fit into their environment. The researchers found that clownfish control their growth to match the size of their anemone host.

In a collaboration with experts at Boston University, the team analyzed the relationship between the size of clownfish anemones. Using a series of lab experiments, the researchers paired clownfish with anemones of various sizes. They discovered that fish on large anemones grow faster than fish on small anemones.

The results explain why clownfish and anemone size are so closely correlated in the wild. The researchers propose that by adjusting their growth, clownfish likely maximize their reproductive value given their anemone context.

Study lead author Dr. Theresa Rueger is a lecturer of Tropical Marine Biology at Newcastle’s School of Natural and Environmental Sciences.

“Anemonefishes are fascinating for their ability to adjust their growth rate to their specific environments, whether that’s to avoid conflict with a larger fish or, as we show here, to make sure they are the ideal size for their anemones,” said Dr. Rueger.

“Anemones are important for the fish because they provide protection from predators and the larger the anemone, the more space the fish has to move around and feed while still being save. If the fish would get too big for the anemone it is on, it might not get enough food or be safe. At the same time the fish wants to be as big as possible to be able to produce lots of offspring.”

“Our data from wild fish shows that anemone size and fish size is very closely correlated: large fish are always on large anemones. And our experiment shows that is not a coincidence but the fish actively regulate their growth to fit their anemone host. This is the first time that this plasticity of growth in a vertebrate has been found to depend on a mutualistic partner, and it shows how important mutualisms are.”

“The next step will be to disentangle the mechanism, what makes the fish decide how large it needs to be? Through our experiment we already know it’s not food availability (all fish got the same amount of food) and it is not space availability alone (the fish did not show the same plasticity when they were on silicone anemones), so it seems to be something about the mutualistic partner itself. Lots of research still to be done!”

The study is published in the journal Scientific Reports.

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By Chrissy Sexton, Earth.com Editor