Think back to the beginning scenes of the ever-popular Disney movie, Finding Nemo. The scene opens with Marlin and his wife, two clownfish watching over their bounty of eggs tucked away safely underneath the tentacles of the sea anemone. Although from a children’s Disney movie, this scene holds a lot of truth and illustrates the famous symbiotic relationship between clownfish and sea anemones.
Typically, a specific species of clownfish will associate with a particular species of sea anemone. However, in the off chance that an anemone is unavailable as a suitable host, clownfish may associate with a non-anemone invertebrate host as a replacement. Here, we will explore the relationship between the clownfish and the anemone, as well look at some unconventional hosts that you may experience in your at home aquarium.
The Classic Relationship Between Clownfish and Anemone
The clownfish and the sea anemone exhibit a mutualistic symbiotic relationship. This means that both species benefit from the other. In the wild, you will find clownfish living within the sea anemone’s stinging tentacles, to which the clownfish is “immune” (I will come back to why immune is in quotations). This act protects the clownfish from larger predators that may consider the clownfish an easy meal. Also, the clownfish’s eggs are given some degree of protection as they are typically laid on the soft substrate underneath the body of tentacles of the anemone.
Due to the symbiotic nature of this relationship, the clownfish is not the only one who benefits. The clownfish contributes to the health of the anemone by feeding on small invertebrates that could potentially harm the anemone. Additionally, the anemone gains nutrients from absorbing the fecal matter of the clownfish. The clownfish also deters butterfly fish from eating the anemone by emitting a high-pitched sound. Lastly, the wiggling and swimming motions of the clownfish serve to increase water flow around the tentacles, which in turn increases available oxygen level for the anemone (Szczebak et al., 2013). Overall, the benefits of this relationship increase the lifespan and reproductive success of both organisms.
This relationship is so strong that sometimes, clownfish will act aggressively towards other fish or invertebrates that attempt to feed on the anemone. Clownfish have even been known to protect their host from human hands by nipping at them if they intrude. Although not as common, they are also known to occasionally bring food to their host anemone, making sure their host is well fed. This act is more common in aquariums as oppose to in the wild.
How Do the Clownfish Tolerate the Stinging Tentacles?
So, how do they do it? How are clownfish able to safely live amongst the dangerous, stinging tentacles of the anemone? Research shows that toxins extracted from the anemone will in fact kill a clownfish. This fact tells us that clownfish are not exhibiting some sort of immunity from the sting, but instead aren’t actually getting stung at all (Mebs, 1994). The “immunity” comes from the coating of sticky mucus that covers the clownfish. Whether the mucus has chemicals that inhibit the discharge of the stinging cells or the mucus is lacking the chemicals that would stimulate discharge of the stinging cells is still unclear (Mebs, 2009).
So with a mutually symbiotic relationship as strong as the clownfish and sea anemone, is it possible that the clownfish will associate with any other organism? Although not as well documented in the literature as the classic pairing, clownfish have been known to associate with non-anemone hosts. If an anemone is unavailable as a suitable host in an aquarium, clownfish will sometimes associate themselves with other cnidarians. Some cnidarians still exhibit the stinging tentacles, similar to the sea anemone, thus providing the same protection to the clownfish.
Clownfish have also been observed associating with giant clams – even when other more suitable cnidarian hosts are available! What’s strange about this relationship is that the benefits are biased to the clam, in that the clam offers no protection to the clownfish. Additionally, sometimes clownfish will take up residence in a species of anemone that does host clownfish, just maybe not that specific species of clownfish.
So, after considering all this, we can ask ourselves, are clownfish content with no substrate to serve as a host? It definitely seems as though clownfish prefer having something to associate with, whether it is a sea anemone or a giant clam – but does the lack of a suitable substrate cause them distress? There are plenty of clownfish that exist in aquariums without a proper host. It’s safe to say that in your home aquarium, clownfish will most likely not turn down a suitable substrate, but in the end, if no suitable substrate is present, they will still carry on living without one.
Szczebak, J.T., R.P. Henry, F.A. Al-Horani, and N.E. Chadwick. 2013. Anemonefish oxygenate their anemone hosts at night. Journal of Experimental Biology: 216:970-976. doi:10.1242/jeb.075648.
Mebs, D. 1994. Anemonefish symbiosis: Vulnerability and resistance of fish to the toxin of the sea anemone.Toxicon: 32(9), p.1059-1068.
Mebs, D. 2009. Chemical biology of the mutualistic relationships of sea anemones with fish and crustaceans.Toxicon: 54(8), p.1071-1074.
Two clownfish on beige anemone: http://scubadiverlife.com/2014/09/21/special-relationship-anemone-symbiosis/
Clownfish associating with stony coral and giant clam: http://www.advancedaquarist.com/2014/3/fish2