A charismatic little blenny, slate-blue at the front and orange at the rear, that perches in rock holes and peers out with big, expressive eyes. Hardy, mostly reef-safe, and an excellent beginner blenny, though it can occasionally nip corals or squabble with other bottom-dwellers.
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Educational only. KinStation content is reviewed by licensed veterinarians but cannot replace an in-person exam. Always consult a licensed veterinarian or board-certified specialist for diagnosis, treatment, or any decision affecting your pet's health.
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Indo-Pacific: from East Africa and the Maldives across to the western Pacific
Origin
Old World
Climate
🌴 Tropical
Water type
🌊 Marine
Family
Blenniidae
Genus
Ecsenius
Part of the Blennies
Blennies are small, bottom-dwelling marine fish with scaleless bodies, blunt heads, and big expressive eyes, often perching on rocks or peering out from holes. The aquarium trade favors them for their comic personalities, useful algae-grazing habits in many species, and suitability for nano and reef tanks.
From the minimum an animal needs to be kept humanely, up to the ideal setup. Bigger is almost always better — minimums are floors, not targets.
Photo coming soon
Minimum
Single nano reef
30 gal / 114 L nano reef
Ecsenius bicolor is a perching algae-grazer. A 30-gallon reef with mature live rock, algae growth for grazing, and multiple holes to claim as a den. Only one per tank — they fight other blennies.
Photo coming soon
Recommended
Reef display
55 gal / 208 L reef
55-gal reef with film algae, plenty of rock perches, and reef-safe tankmates. Supplement with nori once algae is grazed down. Generally reef-safe but may sometimes nip LPS.
Photo coming soon
Ideal
Mature mixed reef
75 gal+ / 284 L+ mature reef
Mature 75-gal+ reef with stable algae and pod growth, varied rock structure, and a single bicolor blenny ruling its preferred cave. Very long-lived in well-tuned systems.
Life & growth stages
How this animal changes through its life — each stage often has its own care, diet and space needs.
Photo coming soon
Egg
Fish eggs are small, translucent spheres, often laid in clutches on plants, substrate, or in a nest — or carried/brooded by a parent in livebearing and mouth-brooding species. A dark eye spot and the curled embryo become visible inside as development progresses.
Photo coming soon
Fry
Newly hatched fry are tiny and semi-transparent, frequently still carrying a yolk sac that fuels them before they feed freely. They lack full fin structure and adult coloration, staying near cover until they can swim and forage on their own.
Photo coming soon
Juvenile
Juveniles look like miniature adults but with developing fins and muted or different markings; many species shift pattern and color as they mature. Growth is rapid at this stage given clean water and steady feeding.
Adult
Adults show the species' full size, finnage, and mature coloration, and are sexually mature. Many fish develop sex-specific differences in size, color, or fin shape, which can intensify during breeding.
Habitat & enclosure
A tank of 30 gallons or more with plenty of live rock full of holes and crevices suits a bicolor blenny, which spends its time perched in or beside a chosen hole that serves as home base. Surface area and hiding spots matter more than open swimming room. A lid is recommended, as blennies can jump when startled.
Maintain stable reef parameters: temperature 72-79 F (22-26 C), pH 8.1-8.4, salinity 1.023-1.026 specific gravity, with low to moderate flow. Lighting can follow coral needs; a mature tank with some algae gives the blenny extra grazing.
Substrate
Fine sand over abundant live rock is standard; the rock's holes and crevices are the essential feature, providing the home hole this blenny defends and sleeps in. Substrate type itself is unimportant.
Equipment & setup
A reliable heater, low to moderate flow, and reef lighting suited to the corals are all that is needed, with a protein skimmer on larger systems. A secure lid helps prevent jumping when the fish is startled.
Diet
An omnivore that grazes algae and detritus from rock and also takes meaty foods. Offer a mixed diet of dried algae (nori), algae-based pellets and flakes, and frozen mysis and brine shrimp, fed two to three times daily. It will graze film and some hair algae naturally but should not be relied on as a dedicated algae mower the way Salarias is.
A varied diet that includes both greens and meaty items keeps it healthy and colorful, and helps reduce any tendency to nip at corals out of hunger.
Behavior & temperament
Generally peaceful and reef-safe, but individuals can be nippy, occasionally picking at LPS coral polyps, clam mantles, or the slime coats of other fish, and they can be territorial toward other blennies, gobies, and dartfish. Keep only one per tank unless it is large, and watch corals after introduction. Most specimens are well behaved, but temperament varies by individual.
It is a bold, expressive fish that perches on its pectoral fins, darts into its hole tail-first when alarmed, and watches the tank with swiveling eyes. Its comic personality and quick color shifts (it can darken or pale with mood) make it a favorite.
Health
Hardy, but susceptible to marine ich and velvet, so quarantine and drip-acclimate before adding to the display. Its scaleless skin is sensitive to copper-based medications and to poor water quality, so use reef-safe treatments where possible and keep parameters stable. Check for a rounded belly and active feeding before purchase.
With a varied diet and stable conditions it is long-lived and trouble-free. The main concern is behavioral, watching for coral-nipping or aggression rather than disease.
Tips, DIY & hacks
Make sure the rockwork offers at least one good hole the blenny can claim, which speeds acclimation and gives it a secure base. Feed plenty of algae-based foods to curb any coral-nipping tendencies, and observe new additions around prized LPS and clams. It is an affordable, personable, hardy choice for a first marine blenny.
