While diving Koh Tao you have the opportunity to see hundreds of different species of fish. Some are brightly colored, while others you might swim right past and not even notice them. Fish come in all different shapes and sizes. One of my favorite fish to see while diving is the filefish. The filefish, also known as a foolfish or leatherjackets, and is closely related to the triggerfish and pufferfish.
Filefish have a rhomboidal body that is flattened. When viewed from the front, top or bottom the fish appears small. When viewed from the side the fish appears larger due to the way its body is flattened. Ranging from brightly colored to cryptic body colorations on their body filefish are very diverse when it comes to their appearance.
Just like their cousins the triggerfish, filefish have a slender retractable dorsal spine on their head. Why they have this spine is not really known, but filefish have been spotted using it to wedge themselves into cracks.
Rough Like Sandpaper
So why are filefish called filefish?
Filefish may appear smooth to the touch, but they are covered in lots of small little scales, which give the appearance that it is smooth, but if you were to feel their skin it would feel like sandpaper.
Sailors are rumored to have used their skin to light matches and even to sand their wooden boats.
What does a filefish eat you may ask? They feed on many different things. They have mouths that are small and tapered into a snout, with specialized teeth that allow them to eat many different things.
Depending on the species of filefish they have been observed eating algae, sea grass, coral, tunicates, jellyfish, and other small invertebrates.
Filefish are shallow water fish and can be found either in pairs or independently depending on the species. They are not very good swimmers, and tend to swim with their head down in a position that may trick predators into thinking they are a piece of seaweed or sea grass.
Some species of filefish possess different coloration as well as body shapes, which allow you to distinguish between male or females. Filefish create nests on the seafloor much like triggerfish where they lay and fertilize their eggs. The parent filefish will usually guard the nest until the young hatch and then the young fish are left to drift in the open ocean.
The Scribbled Filefish
One of the species of filefish you may glimpse in the waters off Koh Tao, is the scribbled filefish, also called scrawled filefish, or scrawled leatherjacket. Having an elongated oval, flat body and an upturned mouth, it definitely stands out from other fish you may see swimming by. Scribbled filefish have olive brown to yellowish bodies with bright irregular blue lines and black spots.
One of the larger species of filefish, as well as their bright coloration makes them fairly easy to spot. They have a thread like dorsal spine which they display when threatened, as well as when they are sleeping to wedge themselves into cracks and crevices.
Here on Koh Tao, scribbled filefish can be spotted fairly regularly at dive sites such as Twins and White Rock swimming above the corals as well as between the cracks. Scribbled filefish have even been seen in deeper dive sites like Chumphon and Southwest.
The Strapweed Filefish
The other species of file fish found around Koh Tao is the strapweed filefish also known as the small-spotted leatherjacket. The strapweed filefish is much smaller than the scribbled filefish and inhabits shallower water then the Scribbled filefish. They can also be seen in Koh Tao. They have a brown or yellowish body covered with small black to brown spots. Unlike the scribbled filefish the strapweed filefish does not appear smooth. Its body is covered in small bumps and projections that help it blend into its environment.
The strapweed filefish also has a much more robust dorsal spine then the threadlike dorsal spine found on its larger cousin. Not much is known about the strapweed filefish, but most people do not know that they are able to camouflage themselves into their surroundings by changing colors based on their mood and outside stress. Very similar to how chameleons change color.
Both species of filefish found around the island are not listed as threatened, but they are under pressure from fishing. Filefish are eaten around the world, and collected for the aquarium trade, which puts pressure on the population of filefish around the island. Educating ourselves and the public, as well as protecting the environment in which the fish live are ways we can better protect the filefish.
If you are interested in learning more about Filefish or any other fish found around Koh Tao, we offer the Fish Identification Specialty which focuses specifically on fish. We also offer the Naturalist specialty which includes both corals and fish identification. For those who are looking to improve their fish and coral identification skills, while also learning how to collect data for the Reef Check database, one can enroll in our Reef Check Course.
Author: Will Nittler (PADI DM #372286)