Clark’s anemonefish feeds its sea anemone
Clark’s anemonefish pass animal food that they do not consume to the sea anemone in which they live, Yuya Kobayashi and colleagues write. It is an extra service.
Anemonefish (or clownfish) and sea anemones are partners for life. The fish protect the sea anemones from predators and parasites, keep them clean, fertilize the water with their excrement and refresh it. Now, Yuya Kobayashi and colleagues show that Clark’s anemonefish, Amphiprion clarkii, also provisions its partner with food. The fish live in large sea anemones on coral reefs in the western Pacific Ocean, the Indian Ocean and the Red Sea, among other places, and have mutual relationships with several species of sea anemones.
In exchange for their services, anemonefish can live safely in an anemone. That is not self-evident, because sea anemones, relatives of jellyfish, have rings of tentacles with stinging cells full of poison around a mouth opening. With these tentacles, they defend themselves and catch prey, which is paralyzed by the poison. But anemonefish move unhindered among the tentacles.
Suitable snacks
That Clark’s anemonefish occasionally attach food to the tentacles, was demonstrated by Kobayashi and colleagues with experiments in the sea off the coast of Japan. The partner of Clark’s anemonefish there is the bubble-tip anemone, Entacmaea quadricolor, named after the bulbous tips of its tentacles. The researchers offered the Clark’s anemonefish pieces of animal food of different sizes: shrimp, squid, clam, fish or sea urchin. They observed what happened or made video recordings that they analyzed afterwards.
The fish can only ingest small pieces, up to about half a centimeter. They ate small pieces of shrimp, squid, clam and fish until they were satiated; if they got more, they placed excess pieces on the tentacles of the sea anemone. Larger pieces, up to 2 centimeters, were provided immediately to the sea anemone. The anemonefish ignored small pieces of sea urchin, but picked up large pieces and gave it to the sea anemone; the fish cannot eat pieces of sea urchin because of their hard armor. Sea anemones usually transported the animal food that was given to the mouth opening and consumed it.
The researchers also offered pieces of plant food to the anemonefish: green algae. The fish ate small pieces but ignored larger pieces. They didn’t give any piece to the sea anemone, which wouldn’t have used it, because it is carnivorous.
So, Clark’s anemonefish feed the sea anemone with food that is suitable: large pieces of animal food including sea urchin, but no green algae.
Extra growth
The food provision is an extra service, but not without self-interest. Clark’s anemonefish are permanent residents of a sea anemone and live in groups of males and one female that deposits her eggs between the tentacles of the sea anemone. If the female disappears, the largest male becomes a female and takes her place. A sea anemone that is fed grows faster and therefore offers more space for fish and eggs.
The question still is whether this feeding in the field frequently happens under natural conditions, without researchers offering bits of animal food. The researchers have observed it, but not very often.
Willy van Strien
Photo: Clark’s anemonefish in bubble-tip anemone. Diego Delso (Wikimedia Commons, Creative Commons CC BY-SA 4.0)
More about anemonefish: good friend
Source:
Kobayashi, Y., Y. Kondo, M. Kohda & S. Awata, 2025. Active provisioning of food to host sea anemones by anemonefish. Scientific Reports 15: 4115. Doi: 10.1038/s41598-025-85767-9
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