False clownfish in anemone

A false clownfish in its anemone home. Image taken at the California Academy of Sciences.

In a previous post, I talked about false clown fish, AKA Nemo fish and I mentioned that Nemo had a very special relationship with his anemone and promised a more detailed discussion. Well, here it is.

First a bit about anemones. They are animals that are related to jellyfish and like jellyfish, they have stinging cells called nematocysts (once again, here is the video of nematocysts firing). These stinging cells are filled with venom and they stun fish, which the anemone then consumes. That being said, it hardly seems like a safe place for a small fish to live. However, the clown fish doesn’t get stung by the nematocysts. This is because it has a slimy protective coating on his body (Scientists have been trying to discover whether the fish makes its own mucus coat or if it gets the mucus from the anemone during an acclimation process. Here is one study that suggests that the fish produce their own mucus.) In some cases, anemones also recognize their partners because of a chemical substance that their partners give off and the anemones will rarely try to sting their partners.

So, why have they evolved to tolerate each other? How does each animal benefit from this partnership? Well, the fish gains the protection of the anemone’s stinging cells for itself and its eggs, as potential predators could be stung and consumed by the anemone.

clown fish in anemone

A false clown fish nestled safely in its anemone's protective tentacles. Image taken at the California Academy of Sciences.

The anemone benefits in many ways. First, the small fish might act as a lure for larger fish to come by that the anemone will then sting and consume. The clown fish will also attack fish that try to nibble on the anemone, such as butterfly fish. Even when the attackers are relatively large, the clown fish will defend its home. The anemone can also eat the left over food from clown fish dinners. Lastly, clown fish nitrogen waste will increase the levels of nitrogen in the water. This is good because some anemones have an algae that lives inside of their tentacles called zooxanthellae (the same type of algae that lives in coral). The zooxanthellae makes sugar from sunlight like a plant and shares some of that sugar with the anemone. The nitrogen from the fish waste fertilizes the zooxanthellae which in turn can increase food production and anemone growth. So as you can see, the anemone gains a lot by offering its protection to these small, attentive fish.