Thanks to the popular Disney/Pixar film Finding Nemo, clownfish are among the world’s most popular fish. Scuba divers hope to encounter them, and aquarists hope to own them. But what’s the real story behind these small, anemone-hugging fish that inhabit tropical waters of the Indo-Pacific? Swim down–I mean, scroll down–to find out!
1. There are 30 species of clownfish
First off, there are 30 species of clownfish, and not all of them resemble the clownfish you may know. In Finding Nemo, Marlin and Nemo are ocellaris clownfish, which are also known as false percula clownfish or common clownfish. Yet, as common as they are, I do not have any decent ocellaris clownfish photos, BUT I do have photos of a variety of other clownfish species that you probably didn’t even know about! Check out the cinnamon clownfish below. A beautiful name for a beautiful fish!
2. They are protected by a thick mucus layer
Clownfish are famous for their special, symbiotic relationship with sea anemones. They protect the anemone from predators and parasites, and they anemone does the same. But why can they live so happily within the clutches of a creature that could easily kill and eat another fish of the same size? Well, the majority of fish are covered in mucus for osmoregulation, protection from parasites, and streamlining, but clownfish take it a step further. Their mucus coat is three to four times thicker than that of other fish, and scientists speculate that it is sugar-based rather than protein-based, preventing the anemone from indentifying them as food. Additionally, clownfish will rub themsevles up against the tentacles of a new host anemone to develop an immunity to its sting. In this manner, the clownfish are protected from the anemone’s deadly, venomous nematocysts (tiny, harpoon-like stinging cells), and they can swim in and out of the tentacles with ease.
3. They are compatible with only 10 species of sea anemone
Despite the symbiotic relationship between clownfish and anemones and the moniker “anemonefish”, clownfish cannot set up shop in any anemone they choose. There are over 100 species of sea anemone in the ocean; yet, of these 100 species, clownfish are only compatible with 10 of them, and of these 10, only select species of clownfish are compatible with select species of anemones. Clark’s anemonefish is one of the few species that is compatible with all 10 clownfish-hosting anemones. For a little more information about the anemones, here’s a list of the 10 clownfish-hosting anemone species.
4. They are omnivores
Clownfish are omnivorous, which means they like a bit of salad to go with their meat. They dine on both zooplankton (small animals floating in the water column) and algae. They also eat parasites that are harassing their anemone host, and they feed on any scraps the anemone leaves behind. Once again, both clownfish and anemone benefit, which is a defining feature of a symbiotic relationship.
5. Their poop provides nutrients for their host anemone
Speaking of eating, clownfish produce a lot of waste, but their waste does not go to waste. Their poop provides nutrients for the anemone, and its nitrogen content increases the amount of algae growing within the anemone’s tissue, which aids in the anemone’s growth and regeneration. The clownfish’s movements around the anemone also improves water circulation, increasing the anemone’s body size and improving respiration for both anemone and clownfish. Who knew poop could be so powerful?
6. They are good parents
In a single anemone, there is one dominant female and multiple males. However, most of the males are juvenile and are too small to breed. Only one male, the dominant male, can breed with the female. Depending on the female’s size, she will lay anywhere from 600 to 1500 eggs, but that is where her parental duties end. Unlike most animals, clownfish parental responsibilities rest upon the male’s shoulders, er, fins. When he does, he cares for the eggs by fanning and guarding them for 6 to 10 days until they hatch.
7. They can change their sex
Now, here’s a fun fact about clownfish that’s not exactly “family friendly” and was not covered by Finding Nemo: all clownfish are born male. So how do a bunch of dudes create a bunch of little Nemos? Well, they use a rather…unconventional strategy. Remember that dominant female I mentioned in #6? She was once a he. Yes, that’s right; clownfish can change their sex. When the dominant female dies, the dominant male changes his sex and becomes the new dominant female. In turn, the largest juvenile male rapidly increases in size and become the new dominant male. Meanwhile, all the other males are candidates for future dominant male and, later, future dominant female. Really changes your outlook on Finding Nemo, huh?
8. They make up 43% of saltwater aquarium fish
Last but not least, clownfish are unsurprisingly among the most coveted and traded of all saltwater aquarium fish, and they make up 43% of the the global marine ornamental trade, along with their close relatives the damselfish. They were one of the first popular saltwater aquarium species to be aquacultured and have been bred for over 40 years. The release of Finding Nemo in 2003 saw a serious uptick in clownfish sales, and I expect the release of Finding Dory in 2016 will cause another spike in clownfish sales in the coming years.
So that’s the clownfish: the tropical, anemone-hugging transvestite. For more information about clownfish and sea anemones, please check out Wikipedia, Animal-World, and Ask Nature. Thanks for reading!