---
title: "Redtoothed triggerfish shows two red upper teeth even with its mouth shut, and uses them to eat plankton"
url: https://badiyaa.com/redtoothed-triggerfish-red-teeth-fangs/
published: 2026-11-13T07:18:00+00:00
modified: 2026-11-13T07:18:00+00:00
section: Pets & Animals
publisher: Badiyaa
---

# Redtoothed triggerfish shows two red upper teeth even with its mouth shut, and uses them to eat plankton

The redtoothed triggerfish shows two long red upper teeth even with its mouth closed, but this Indo-Pacific reef fish mainly eats plankton and crustaceans.

The redtoothed triggerfish has a grin built for a horror poster: two long, blood-red upper teeth that stay on show even when its mouth is shut. Photos of the “fanged” blue fish are doing the rounds again online, and the real story behind those teeth is gentler than they look.

This Indo-Pacific reef fish, *Odonus niger*, is the only species in its genus. It is also one of the calmer members of a family famous for bad tempers.

## What the red “fangs” actually are

The two visible teeth are simply the front of the upper jaw. A public aquarium on the Oregon coast that keeps the species describes them as long upper teeth that remain visible with the mouth closed. Behind them sit more small, needle-sharp teeth, all tinted red.

Triggerfish as a family have small, strong jaws with teeth adapted for crushing shells, a feeding style biologists call durophagy. Each jaw carries a row of four teeth on each side, and the upper jaw has six extra plate-like teeth farther back in the throat.

## What it uses them for

Here the redtooth breaks from its relatives. Most triggerfish crunch slow, armored prey such as crabs, clams and sea urchins. The redtoothed triggerfish is one of the few in the family that mainly eats plankton.

Its diet is broad and opportunistic:

- **Crustaceans**, its main food in the wild

- **Zooplankton** picked from the current

- **Sponges and algae**

- **Squid and small fish**, whose remains have turned up in stomach studies

So the “fangs” work more like tweezers and nippers than weapons, letting the fish pluck drifting animals and scrape food from the reef.

## Why red? No one source has a firm answer

The species is named for the color, but neither the encyclopedia entry nor the aquarium’s species profile explains what the red tint does. It is fair to treat any confident claim about a purpose, from warning signals to diet, as unconfirmed until a study tests it.

What the sources do agree on is that the color of the body changes. The fish can shift from purple to blue or bluish green with mood, food and water quality, and its head can turn yellowish.

## A fish that locks itself in

The “trigger” in the name comes from the dorsal fin. When a triggerfish raises its tall first spine, a short second spine locks it upright, and only pressing that second “trigger” releases it. A frightened redtooth dives into a favorite reef hole and wedges itself in place with the locked spine.

It swims in an unusual way too. Its pectoral fins are small, so it steers and pushes with rippling dorsal and anal fins, a style called balistiform locomotion.

## Size and range at a glance

Most adults measure 9 to 12 inches (23 to 30 centimeters), and the aquarium lists a maximum of 50 centimeters, about 20 inches. The fish ranges from the Red Sea and East Africa east to the Marquesas and Society Islands, north to southern Japan and south to the Great Barrier Reef. Adults gather in large schools along current-swept reef slopes at depths of roughly 5 to 40 meters.

In the breeding season one male can spawn with over 10 different females inside his patch of reef in a single day, and both parents guard the nest.

For more strange reef and ocean senses, read how [sharks and rays detect the electric fields of hidden prey](https://badiyaa.com/sharks-ampullae-of-lorenzini-electric-sense/), or meet the [Humboldt squid that swarm in shoals of 1,200](https://badiyaa.com/humboldt-squid-size-shoals-red-devil/).

The species is listed as Least Concern on the IUCN Red List, according to a 2022 assessment, and is caught for food in Papua New Guinea, the Philippines and Indonesia.

## Further reading

- [Wikipedia: Redtoothed triggerfish](https://en.wikipedia.org/wiki/Odonus_niger)

- [Wikipedia: Triggerfish](https://en.wikipedia.org/wiki/Triggerfish)

*Image: Diego Delso, CC BY-SA 4.0 via Wikimedia Commons*

*This article was produced with AI assistance and reviewed by our Editorial Desk. [How we work](https://badiyaa.com/editorial-policy/).*