Filefish

1. Living Sandpaper

Run your hand along a filefish (if it lets you), and you’ll feel why they got their name. Their skin isn't slimy like most fish; it’s covered in tiny, rough scales that feel exactly like sandpaper. In the days before Home Depot, sailors and carpenters actually used dried filefish skin to sand down wooden boats and finish furniture. They are quite literally swimming tools.

2. The "Unicorn" Horn

That prominent spine on their head isn't just for show—it’s a survival multi-tool. When threatened, a filefish can erect this spine and lock it in place with a second, smaller spine behind it. This allows them to wedge themselves tightly into reef crevices. A predator might be able to grab the tail, but they’ll never pull the fish out. It’s the ocean’s version of a doorstop.

3. Headstand Masters

If you see a fish floating upside down, it’s usually bad news. But for the filefish, it’s just Tuesday. To blend in with their surroundings, they often swim head-down, aligning their bodies perfectly with vertical seagrass blades or branching corals. By drifting with the current in this posture, they become indistinguishable from a floating leaf or a piece of debris, fooling predators and divers alike.

4. The Invisible Fin Trick

Filefish are masters of the "hover". They don't use their tail for normal swimming; instead, they undulate their transparent dorsal and anal fins in a rapid, wave-like motion. This allows them to move with incredible precision—forward, backward, or holding perfectly still—without their body seemingly moving at all. It’s like they are levitating by sheer willpower.

5. Not Just a Pretty Face

While they look goofy, some filefish are hardcore predators. The Scrawled Filefish, for instance, snacks on things that would send other fish to the ER—including stinging jellyfish and hydroids. They seem to be immune to the nematocysts (stinging cells), munching on toxic tentacles as if they were spicy noodles.

6. Evolution Stole Their Legs

Evolution decided filefish didn't need pelvic fins (the fish equivalent of hind legs). Instead, they have a single, modified pelvic spine or a fleshy flap on their belly. In some species, this has disappeared entirely. It helps streamline their profile for that "flat pancake" look, perfect for slipping into narrow hiding spots.

7. The "Leatherjacket" Gang

In Australia and parts of Asia, you’ll hear divers calling them "Leatherjackets". This nickname comes from their tough, thick skin which, when prepared for cooking, peels off in one piece like a jacket. It’s a testament to just how durable their outer armor really is compared to the delicate scales of other reef fish.

8. Master of Textures

Camouflage isn't just about color; it's about texture. The Tasseled Filefish (or Prickly Leatherjacket) takes this to the extreme by growing fleshy, weed-like flaps all over its body. It looks less like a fish and more like a fuzzy piece of coral. You could be staring right at one and swear it’s just part of the reef until it blinks at you.

9. Sleepy Biters

Bedtime on the reef can be dangerous with currents sweeping you away. To get a good night's sleep, some filefish clamp their mouths onto a piece of coral or sponge, effectively tethering themselves in place. It’s a secure way to snooze without waking up miles away from home.

10. Ciguatera Roulette

A word of warning for the gourmets: while filefish are eaten in some cultures, large specimens are notorious for accumulating Ciguatera toxin. Because they graze on algae and small invertebrates on the reef, they concentrate toxins from the food chain. Eating a large filefish can be a game of Russian roulette with your nervous system—best to leave them on the reef.