FaunaHub

Blenny (family Blenniidae)

FishCoral reefMarine

Midas blenny (Ecsenius midas), a slender golden reef fish with big eyes.

Midas blenny (Ecsenius midas).

Image: Jason Marks, CC BY-SA 3.0, via Wikimedia Commons.

Overview

Blennies (family Blenniidae, the combtooth blennies) are small, charming fish of reefs, rocky shores, and tide pools, full of personality. Most are only a few centimetres long, with blunt, rounded heads, large high-set eyes, and a tapering, scaleless body, and many sport feathery skin flaps (cirri) above the eyes like little eyebrows. They are typically bottom-dwellers that perch on rocks and coral or peer out from holes, often with just the head poking out.

Blennies are a large and varied group, and some are remarkable: the sabre-toothed “fang blennies” and the famous mimic blenny that copies the cleaner wrasse to sneak bites from bigger fish.

Note: “blenny” covers a large family (and the name is loosely used for other small elongate fish too); details here describe the combtooth blennies broadly. Treat general statements as approximate and verify against authoritative sources.

Habitat & Range

Blennies live in shallow seas around the world — coral reefs, rocky reefs, seagrass beds, and intertidal rock pools — with the greatest variety in warm tropical waters. They keep close to the bottom and to shelter, occupying small holes, empty worm and barnacle shells, and crevices into which they can dart, and a few even venture briefly out of water on wet rocks.

Diet

Blennies have varied diets: many are grazers that nibble algae and tiny organisms from rocks and coral with their comb-like rows of teeth, while others feed on small invertebrates or plankton. The fang blennies are different again — armed with venomous fangs and, in some, a taste for biting chunks of skin, scales, or mucus from other fish.

Behavior

Blennies are entertaining to watch: alert and inquisitive, they perch on the bottom, dart between shelters, and often back into a hole to peek out with just their big-eyed face showing. Many are territorial, and males of various species guard nests of eggs laid in a crevice or shell. The family includes some famous tricksters — fang blennies have grooved, venomous fangs, and the sabre-toothed mimic blenny imitates the colours and “dance” of the cleaner wrasse so it can approach larger fish expecting to be cleaned, then dash in to bite off a mouthful of skin or fin before fleeing. Tide-pool blennies are remarkably hardy, tolerating the heat, low oxygen, and exposure of shoreline pools.

Human Interaction & Conservation

Blennies are favourites of divers, snorkellers, and tide-pool explorers for their bold, characterful behaviour, and many small species are popular and useful algae-grazers in marine aquariums. They are harmless to people (the fang blennies' venom is used defensively and is not dangerous to humans). As reef and shore fish they depend on healthy coastal habitats, so reef degradation and pollution are the main concerns, while most species remain common. Consult authoritative sources for status.

More photos of the blenny

A combtooth blenny peering out, showing its blunt head and big eyes.

Blenny (family Blenniidae).

Image: Rickard Zerpe, CC BY-SA 2.0, via Wikimedia Commons.

Frequently Asked Questions — Blenny

What does a blenny look like?
Most blennies are small fish, just a few centimetres long, with a blunt, rounded head, large high-set eyes, and a smooth, scaleless, tapering body. Many have feathery skin flaps (cirri) over the eyes that look like little eyebrows. They're usually seen perched on the bottom or peeking out of a hole with just their face showing.
Is it true some blennies mimic cleaner fish?
Yes — the sabre-toothed mimic blenny is famous for it. It copies the colours and swimming 'dance' of the cleaner wrasse, a fish that bigger fish let approach to remove parasites. Fooled into expecting a cleaning, a large fish lets the mimic come close — and the blenny dashes in to bite off a mouthful of skin, scales, or fin before darting away. It's a remarkable case of deceptive mimicry.
Do blennies bite or sting people?
No, blennies are harmless to humans. Some 'fang blennies' do have venomous fangs, but the venom is used to deter predators (and to make biting other fish easier), not against people, and it isn't dangerous to us. Most blennies are peaceful little grazers that are far more likely to hide in a hole than to bother a diver.
What do blennies eat?
It varies. Many blennies are grazers that nibble algae and tiny organisms off rocks and coral with comb-like teeth; others eat small invertebrates or plankton. The unusual fang blennies feed in part by biting skin, scales, or mucus from other fish. As a family, blennies fill a wide range of small-fish feeding roles on the reef and shore.

Sources and further reading

Authoritative wildlife references used for general educational context. Conservation status should always be verified against current IUCN Red List data. External links open in a new tab.