Bicolor Blenny (Ecsenius bicolor)

The Bicolor Blenny (Ecsenius bicolor) is the fish that turns a hole in your rockwork into a face. The front half is a deep slate blue, the back half flares into bright orange, and the two colors meet in the middle like the fish was dipped. It spends its day propped on its pectoral fins scanning the tank, grazing film algae off the rocks, then reversing into a crevice tail first the second something startles it. Hardy, cheap to feed, endlessly watchable, and a genuinely useful algae grazer. Browse the rest of our saltwater livestock and supplies to build the tank around it.

Care Guide

• Tank size: 30 gallons or larger. Blennies do not need swimming room so much as territory and hiding options.
• Rockwork is the whole game: give it mature live rock with plenty of small holes and crevices. A Bicolor Blenny wants two or three back-up bolt holes it can reverse into, and a fish with good cover is a fish you actually see.
• Water parameters: 72 to 78°F, pH 8.1 to 8.4, salinity 1.020 to 1.025. Undemanding once settled.
• Feeding: mostly herbivorous. Film algae on the rocks is a start but never enough on its own, so feed dried seaweed on a VeggieMag clip and a marine algae based flake or pellet. An underfed Bicolor is the one that starts sampling coral, so keep the greens coming.
• Lid: required. Blennies are committed jumpers and this one is no exception.
• How many: one per tank. They are peaceful toward almost everything, but another blenny or a similarly shaped bottom perching fish reads as a rival.

Specifications

Compatibility

Peaceful with the general community and a good fit alongside the Ocellaris Clownfish, Black Ice Longfin Clownfish, Royal Gramma, Banggai Cardinal, Blue Green Chromis, and Firefish Goby. Inverts are completely safe, including the Scarlet Skunk Cleaner Shrimp and the rest of your cleanup crew.

One blenny per tank. This is the main rule. Our Tailspot Blenny, Midas Blenny, Canary Blenny, and Lawnmower Blenny are all great fish, but treat them as alternatives to this one rather than additions to it. Two blennies competing for the same perches in the same rockwork rarely ends well outside a very large system.

The coral caveat. Bicolors are usually model reef citizens, but a few individuals develop a taste for clam mantles or fleshy LPS. Keeping them well fed on greens is the single best prevention, and it is worth watching a new one for the first couple of weeks in a tank with clams.

Recommended Foods & Supplies

• Two Little Fishies SeaVeggies Green Seaweed with a VeggieMag clip
• Ocean Nutrition Green Marine Algae
• Vitalis Marine Grazing Pellets
• Hikari Seaweed Extreme
• Piscine Energetics PE Mysis as an occasional treat

FAQ

Will it clear my algae?
It will graze film algae off rock and glass all day, which is genuinely useful, but it is not a hair algae solution and it will not replace a proper cleanup crew. Think of it as steady maintenance rather than a cure.

Mine changed color. Is something wrong?
Almost certainly not. Bicolor Blennies shift shade with mood, and a fish can go from bright orange and blue to washed out grey and back within minutes. Rapid color change is normal blenny behavior, not a symptom.

Why does it keep hiding?
Because that is the job description. A new Bicolor spends its first days mostly inside a hole, peeking out. Once it decides the tank is safe it will spend more and more time out on the rocks, and it learns feeding time quickly.

Is it safe with my corals?
For the large majority of them, yes. The exceptions are clam mantles and fleshy LPS, which a small number of individuals decide to sample. Feed plenty of seaweed and greens and the risk drops off sharply.