Bicolor Blenny (Ecsenius bicolor) saltwater aquarium fish portrait

The Bicolor Blenny (Ecsenius bicolor) is an elongated, almost eel-like reef blenny found throughout the Indo-Pacific, from the Red Sea and Maldives region through Sri Lanka, the Philippines, and Micronesia and south to the Great Barrier Reef. It inhabits shallow reefs, lagoons, and rubble and crevice zones at depths of roughly 3 to 40 feet or more. The name refers to its striking two-tone pattern: a dark blue-gray, purple, or brown front half that transitions abruptly into a bright orange, yellow, or reddish-brown rear. Large protruding eyes topped with blue-rimmed cirri and comb-like grazing teeth complete the look. Adults reach about 4 to 4.5 inches, and males tend to grow larger than females, display more vivid blue coloration during breeding, and carry extended dorsal and anal fin elements.

Plan on a minimum of 30 gallons for a single fish, with 55 gallons or more if a pair is the goal. Maturity matters as much as volume here. A system that has been running for at least three or four months with visible diatom and film algae gives this grazer the natural forage it depends on, and specimens placed in sterile new tanks frequently decline. Build the aquascape from porous live rock arranged into numerous crevices, caves, ledges, and perches at varying heights, since this is a rock-dwelling hopper rather than an open-water swimmer and will quickly claim a favorite lookout.

Secure the rockwork with epoxy or careful stacking, because a Bicolor Blenny digs in the sand bed and shifts rubble and empty shells around its territory. A tight-fitting lid is not optional. This species is an accomplished jumper and is a well-known carpet surfer in open-top systems.

On the reef, Ecsenius bicolor spends its day rasping marine algae and biofilm from rock surfaces with its comb-like teeth. That grazing habit should continue in the aquarium, so ongoing access to naturally occurring micro and film algae forms the foundation of its nutrition. Supplement that base with seaweed and marine algae-based prepared foods such as dried sheet algae, spirulina flake, and herbivore pellets. Frozen, freeze-dried, or vitamin-enriched brine shrimp, along with finely chopped mysis or krill, round out the menu and help keep a grazing fish in good weight.

Offer small portions about twice daily rather than one large feeding, which matches the near-constant nibbling pattern of a natural grazer. Because a freshly established system offers little to graze on, the tank should carry mature algae growth before this blenny is introduced. A well-fed specimen holds better color and body condition and is far less likely to seek out alternative food sources among the corals.

Film Algae Dried Seaweed Sheets Spirulina Flake Herbivore Pellets Enriched Brine Shrimp Chopped Mysis Shrimp Chopped Krill
This is a peaceful, largely solitary bottom and rock dweller that spends little time in open water, instead hopping between perches and surveying the tank from a favored ledge. It can defend its chosen territory, and aggression tends to increase in smaller aquariums. Squabbles have been reported with other blennies, small gobies, dartfish, and fish of similar shape or coloration, including Royal Gramma, Bicolor Pseudochromis, and Bicolor Angelfish. Keeping a single Bicolor Blenny per tank is the safest approach given conspecific aggression, though mated pairs can be maintained in larger systems and may spar before spawning. The species has been bred in captivity, with both parents guarding the eggs until hatching.

Tangs, butterflyfish, and damselfish make suitable companions. Avoid any predator large enough to view a 4-inch blenny as a meal, including scorpionfish, groupers, lionfish, hogfish, frogfish, parrotfish, and ribbon eels. In the reef aquarium this fish is reef safe with caution: most specimens leave sessile invertebrates alone, but underfed or crowded individuals have been observed nipping at clam mantles and fleshy LPS and SPS corals. Generous rockwork, established algae growth, and consistent feeding keep that risk low.

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FAQ

Frequently Asked Questions

About the Bicolor Blenny

  • How big of a tank does a Bicolor Blenny need?
    A minimum of 30 gallons suits a single adult, and 55 gallons or more is recommended for a pair. The system should be well established with visible algae growth before the fish is added.
  • Is the Bicolor Blenny safe with clams and corals?
    It is reef safe with caution. Most specimens ignore sessile invertebrates, but underfed or crowded fish may pick at clam mantles and fleshy LPS or SPS corals, so regular feeding and ample rockwork matter.
  • Does a Bicolor Blenny jump?
    Yes, this species is a well-known jumper and will leave an open-top aquarium. A tight-fitting lid or secure screen top is essential.