This 15-inch-long, gray-and-yellow fish has a serious overbite and looks like it needs to go to the dentist! While diving, you often hear this fish before you see it. It uses its very-powerful set of fused teeth to bite off pieces of the living coral reef, digesting algae and coral tissue.
Underwater, when it is feeding, it sounds like someone is hitting the reef with a hammer. At night when ‘o‘ili sleeps, it often clamps its jaws down on a live coral so it does not drift away, much like us putting on the emergency brake while parking our car on a hill.
The barred file-fish is quite large when viewing it from the side, but very skinny looking at it straight on. Like most fish, when it is alarmed by a diver it will turn sideways to look as big as it can. And it has a two-inch-long, yellow-colored dorsal spine it can make erect, which makes it look even bigger. Just like the similar trigger-fish, ‘o‘ili can dart into a cave or crack in the reef and make its spine erect, which locks it into the cave so it cannot be pulled out backward by a potential predator.
The Hawaiian word “‘o‘ili” means to sprout or come up, which describes the movements of the dorsal spike. And the name “file-fish” comes from the texture of the small scales on the skin that are as tough as sandpaper. In old Hawai‘i, they would catch and dry out the skin, which could be used to sand the wood on a canoe!
When you see ‘o‘ili by itself, it is usually a bland, gray color. But often you will see them in pairs, and the male will turn yellow and orange and develop gray bars on its sides. Many of our Hawaiian fish will change colors while mating, and that sometimes causes people to think it is a different fish species. When you are attempting to identify a fish while snorkeling, it is best to look at the shape of the fish, not the color, as that can change quickly.
You can see ‘o‘ili in action upon the underwater educational web page, underwater2web.com in the movie “The World’s Guide To Hawaiian Reef Fish.” Upon the web we also have a Hawaiian species-identification link and over 100 underwater educational movies that will soon be released to our schools so our local kids can learn all about Hawaiian marine life from whales to octopus!
Terry Lilley is a marine biologist living in Hanalei. He is co-founder of Reef Guardians Hawai‘i, a nonprofit on a mission to provide education and resources to protect the coral reef. To donate to Reef Guardians Hawai‘i, go to reefguardianshawaii.org.
Source: The Garden Island