Blenny

Blenny key facts

Care level

Beginner-friendly

Lifespan

3-6 years

Size

8-10cm

Diet

Algae, pellet food

Tank

60L+

Role

Excellent algae cleaner

Temperament

Shy but bonds easily with owner

Compatibility

No conspecifics — careful with other blennies

Notes

Reef-safe — loves hiding in crevices

About Blenny

The Bicolor Blenny (Ecsenius bicolor) is a small reef fish widely distributed across the Indo-Pacific, from the Indian Ocean to the western Pacific. Adults reach 8–10 cm and are instantly recognizable by their split coloration: a muted brown front half and a vivid orange rear half that makes them look almost like two different fish. Small skin flaps above the eyes, combined with large expressive eyes, give them an endearingly comical face that aquarists find irresistible. Temperamentally, they are peaceful and undemanding, claiming a rock crevice as home base while generally ignoring other species. Their herbivorous diet of microalgae and filamentous growth makes them natural algae controllers, and they thrive in reef aquascapes rich with live rock. Watching them flit from perch to perch, grazing diligently and staring back at the viewer, never gets old. With proper care they can live 3–6 years, making them a rewarding long-term companion for beginners and experienced reef-keepers alike.

7 things to know before welcoming a Blenny

1. 1Excellent Algae Grazer

   Bicolor Blennies primarily feed on algae and actively graze on live rock and aquarium glass. They help naturally control excess algae growth, making them useful tank cleaners. However, algae alone does not provide complete nutrition, so supplement their diet with quality pellet or flake foods.

2. 2Love of Rocky Hiding Spots

   Bicolor Blennies have a natural habit of tucking into crevices and small holes in rockwork. Providing ample live rock or artificial hiding spots helps them feel secure and reduces stress. Fish that initially hide often become more active and visible once they settle into their environment.

3. 3Territorial Tendencies

   Bicolor Blennies can display territorial behavior toward their own species or similarly shaped bottom-dwelling fish. In smaller tanks, keeping multiple individuals is generally not recommended. They tend to coexist peacefully with calm reef fish and gobies, so choose tankmates accordingly.

4. 4Tank Size Requirements

   Given that adults reach 8–10 cm, a tank of at least around 100 liters is generally recommended. Rather than open swimming space, prioritizing ample rock structure and substrate area is more important for this species. A well-aquascaped tank helps reduce stress and encourages natural behavior.

5. 5Water Quality Guidelines

   A water temperature of 24–26°C and specific gravity of 1.023–1.025 are appropriate targets. This species is sensitive to ammonia and nitrite, so introducing it to a fully cycled and established tank is strongly advised. Regular partial water changes, approximately once a week, help maintain stable water quality.

Frequently asked questions about Blenny

Q.Is the Bicolor Blenny safe in a reef tank with corals?

A.Bicolor Blennies are generally considered reef-safe and do not actively prey on corals. Occasionally, individual fish may nip at the mantles of large-polyp stony corals or clams, so it is worth observing behavior during the first few weeks after introduction.

Useful tools for Blenny care

Learn more about Blenny in the encyclopedia

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