I’d never heard of filefish before I started writing this post. But I was browsing one of the websites I use to get ideas for posts, and the name filefish caught my eye. I always like it when fish are named after other animals or objects because I get to picture a cross between a fish and whatever that fish is named after. Today I thought of a metal file with fins and great big googly eyes, and got a good chuckle out of it. So let’s learn about filefish today, and though you may be disappointed to learn that filefish are not actually a file/fish hybrid, they are pretty cool.

Filefish belong to the family Monacanthidae, which has 27 genera and 102 species. They are fairly widespread, being found in the Atlantic, Pacific and Indian Oceans. Australia is a particularly abundant area for filefish, with over half of all filefish species living in Australian waters. They prefer shallow areas, rarely venturing below depths of 30 meters. Filefish are commonly found in lagoons, reefs, and seagrass beds.

Aluterus scriptus is the biggest species of filefish, and can grow to over 110cm. Image by Choo Tee Yong Vincent, CC BY-SA 3.0, via Wikimedia Commons

Filefish range in size from below 60 cm to 110 cm, depending on the species. They are laterally compressed (meaning their bodies are tall and thin, like they’ve been put in a press and squished), and are shaped a bit like rhomboids. Filefish have two spines on their heads, one of which is much larger than the other. The spines are retractable, and the second, smaller spine holds the bigger spine up when it is erect. Filefish are coloured in a range of hues and patterns, mostly to blend in to their environment.

This type of colouration is vey important to filefish. They have small fins, and so are pretty bad swimmers. This means they can’t easily get away from predators, so camouflaging among corals and sea grass is super important. For filefish that eat invertebrates (some species subsist solely on algae, seagrass, or coral), cryptic colouration also helps hide them from their prey. Some filefish hide out in rock crevices, and use their spines to stay lodged inside if a predator tries to eat them.

Filefish come in such an array of beautiful colours. Image by Julian Finn / Museum Victoria, CC BY 3.0, via Wikimedia Commons

Filefish lay eggs on the ocean floor, in nests prepared by the males. Species differ in terms of parental care; in some species both parents guard the nest, while in others that task is left solely to the male. Once the young filefish hatch, they simply drift in the open ocean, often living within Sargassum seaweed species.

I’ve told you a lot about filefish, but I’ve left out the most important fact: why filefish are called filefish. Unfortunately, the reason is fairly mundane. They are thin and have rough skin, which I guess reminded people of files. In fact, it’s said that dried filefish skin was used as a tool to sand wooden boats. In any case, I’m going to leave you with a picture of what a real filefish should look like. Enjoy!

Cover image by Diver Vincent, CC BY-SA 3.0, via Wikimedia Commons