Bicolour Blenny

Bicolour Blenny

The Bicolour Blenny (Ecsenius bicolor) is a small, endearing reef fish full of personality. Its two-tone body — typically dark blue at the front fading to orange behind — and its habit of perching in rock holes with big eyes peering out have made it a long-standing favourite. Hardy, inexpensive and useful as an algae grazer, it is an excellent first blenny for a community reef.

Like many blennies, it spends its day hopping between perches and grazing surfaces, retreating to a favourite hole that it claims as home.

Natural Habitat & Origin

Ecsenius bicolor is widespread across the Indo-Pacific, where it lives on coral reefs, perching on and darting between rock and coral. It shelters in small holes and crevices in the reef, using them as a base from which to graze the surrounding surfaces.

In the aquarium it wants exactly that: live rock with small holes and crevices to occupy, and plenty of grazing surface with natural algae.

Care Requirements

Maintain stable marine conditions: salinity around 1.024–1.026, pH 8.1–8.4, and a temperature of about 24–26°C (75–79°F). Reaching about 11 cm (4.3 inches), it can be kept in tanks of around 75 litres (20 US gallons) or more. A secure lid is sensible, as blennies can jump, and ample rockwork gives it the perches and bolt-holes it needs.

It is hardy and undemanding, making it forgiving of beginner mistakes provided water quality is stable.

Diet & Feeding

The Bicolour Blenny is primarily a herbivore, grazing on algae and detritus from rock surfaces. Provide a diet built around marine algae and herbivore preparations — including spirulina and dried algae — supplemented with the occasional meaty marine food. A tank with healthy film and turf algae greatly benefits it, and it can help keep such algae in check, though it should not be relied on as a sole algae-control measure.

Behavior & Temperament

This is a generally peaceful, comical fish, though it can be territorial toward other blennies or fish that compete for its perches and grazing patches. It is usually best kept as the only blenny in smaller tanks. Toward unrelated species it is well behaved, spending its time perched and grazing.

Tank Mates

Good companions are peaceful reef fish — clownfish, gobies, chromis, cardinalfish and similar — that won't compete for the same niche. Avoid keeping it with other small bottom-perching blennies in a small system. It is reef-safe, though an occasional individual may nip at clam mantles or coral polyps if underfed; a well-fed blenny rarely causes trouble.

Breeding

Ecsenius bicolor lays eggs in a crevice or hole, guarded by the male, and has been bred by dedicated hobbyists. Rearing the larvae requires suitable small foods and is uncommon, so most trade specimens are wild-collected.

Common Health Issues

The Bicolour Blenny is hardy but, like all marine fish, can be affected by marine ich (Cryptocaryon irritans) and marine velvet (Amyloodinium ocellatum) under stress. Quarantine new arrivals, keep water quality stable, secure the lid against jumping, and ensure it has enough to graze on. Given those basics it is one of the most rewarding and beginner-friendly small marine fish, full of character for a peaceful reef.