Will a Bicolor Blenny eat my corals?

They are generally considered reef-safe and usually ignore corals entirely. However, if they are underfed or lack sufficient algae to graze on, some individuals may occasionally nip at the fleshy mantles of clams or the polyps of LPS corals.

Can I keep two Bicolor Blennies in the same tank?

It is not recommended unless you have a very large aquarium (over 400 litres) with abundant rockwork, or a confirmed mated pair. They are highly territorial towards their own kind and will fiercely fight over hiding spots.

Why is my Bicolor Blenny changing colour?

Bicolor Blennies can rapidly alter their colouration, often appearing mottled, pale, or displaying white bands. This is a natural reaction to stress, territorial disputes, or simply their nocturnal camouflage when the aquarium lights go out.

Why does my blenny always hide in the rocks?

This is entirely natural behaviour. In the wild, they rely on empty worm tubes and small crevices to escape predators. They spend most of their time perched in or near these holes, observing their surroundings.

Does the Bicolor Blenny need a lid on the tank?

Yes. Like many slender, reef-dwelling fish, they possess a strong startle response and are known jumpers. A secure, tight-fitting lid or mesh cover is essential to prevent them from leaping out of the aquarium.

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Bicolor Blenny

Ecsenius bicolor

A charismatic and highly popular marine fish, the Bicolor Blenny is cherished by aquarists for its comical personality, distinct two-toned appearance, and practical algae-grazing habits.

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Ideal Conditions

Temperature: 24 – 27 °C
pH range: 8.1 – 8.4
Hardness: 8 – 12 dGH
Salinity: 1.02 – 1.025 SG
Adult size: 8 – 11 cm
110L: 110 litres+
Lifespan: 2 – 5 years
Diet: Herbivore-leaning omnivore
Water flow: moderate
Preferred setup: Ample live rock with numerous small crevices and caves for hiding, alongside established microalgae growth for grazing.

About the Bicolor Blenny

The Bicolor Blenny (*Ecsenius bicolor*) is a staple in the marine aquarium hobby. Renowned for its bold, bipartite colouration and expressive, prominent eyes adorned with tiny cirri, it brings a tremendous amount of character to the reef tank. This species spends much of its time perched upon rocky outcrops, carefully surveying its environment, or darting backwards into tight crevices when startled. Its endearing habit of resting its head just outside its burrow makes it a delightful subject for observation.

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Is it right for your tank?

Check Bicolor Blenny against a habitat you already keep. We compare water type, temperature, pH, adult size, group needs and everything living there.

Where Bicolor Blenny comes from

Native range

Indo-Pacific, Great Barrier Reef, Micronesia

Countries / regions

Australia, Indonesia, Maldives, Philippines, Japan

Habitat

Clear lagoons and seaward reefs, typically dwelling in shallow waters among mixed coral and rocky substrates where they inhabit empty worm tubes and small crevices.

Widespread across the Indo-Pacific region, primarily found between 1 and 25 metres in depth.

Similar species

Tailspot Blenny
Ecsenius stigmatura
Midas Blenny
Ecsenius midas
Lawnmower Blenny
Salarias fasciatus
Tribal Blenny
Ecsenius tigris

We’re adding more full species guides as the catalogue grows.

Compatible tank mates

Reviewed guidance based on this species' recorded traits.

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Ocellaris Clownfish
Amphiprion ocellaris
Peaceful and occupies the mid-to-upper water column, avoiding territorial disputes over rockwork.
Great
Firefish
Nemateleotris magnifica
A docile tankmate that hovers in the water column and does not compete for the blenny's benthic hiding spots.
Great
Skunk Cleaner Shrimp
Lysmata amboinensis
A beneficial invertebrate that is entirely safe from the blenny and provides excellent cleaning services.
Great
Algae Blenny
Salarias fasciatus
Keeping multiple blennies or competing benthic grazers in the same tank usually leads to severe territorial aggression unless the aquarium is exceptionally large.
Compatible with caution
Tridacna Clams
Tridacna spp.
While generally reef-safe, Bicolor Blennies have been occasionally known to nip at clam mantles or large-polyp stony corals, particularly if underfed.
Compatible with caution
Red Lionfish
Pterois volitans
Large predators will easily view the slender Bicolor Blenny as a convenient snack.
Not recommended

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