Bicolor Blenny

Geographic Origin and Biotope: MARINE species native to Indo-Pacific coral reefs (Maldives to the Great Barrier Reef, Micronesia). Inhabits clear coastal lagoons and rocky slopes rich in microalgae and hard corals.

Taxonomy and Morphology: Bicolor Blenny (Ecsenius bicolor). Small fish of the Blenniidae family. Scaleless body, movable eyes placed high on the head that give it a "human" or funny expression, and small cirri (little antennas) above the eyes.

Social Behavior: Curious, extremely comical and intelligent. Finds a hole in a rock that it elects as "home" and backs into it, sticking out only its head to observe the environment. Moves by hopping from one rock to another.

Coloration and Sexual Dimorphism: Classic "bicolor" livery: the anterior half of the body is dark black/purple, while the posterior half is vibrant orange-yellow. There are variants that are almost entirely bluish or brown. Adult males may show longer caudal filaments.

Aquarium Setup: Nano-reef or community aquarium of minimum 100 liters (25 gallons). Many porous live rocks with natural holes for hiding are vital. Not demanding on lighting, but enough light to grow microalgae is beneficial.

Diet and Feeding: Omnivore with a strong herbivorous preference. Scrapes microalgae and algal film from rocks and glass all day. In the aquarium, it must be fed daily with flake foods or pellets based on Spirulina or seaweed (Nori).

Water Quality: Classic reef aquarium parameters: Salinity 1.023-1.025, pH 8.1-8.4, zero ammonia and nitrites. Sensitive to pH drops and nitrate accumulation which depress its immune system.

Compatibility and Tankmates: Excellent for reef aquariums (Reef Safe). Peaceful towards other fish. May show extreme territoriality towards other Blennies of the same species or fish of identical shape and color. Occasionally (rarely) may nip at clam mantles or fleshy LPS corals.

Aquarium Reproduction: The male attracts the female to his rocky hole to lay adhesive eggs, which he will then fiercely guard until hatching. Reproduction recorded but rearing the microscopic pelagic larvae is for experts.

Risks and Diseases: Blennies are scaleless fish, thus vulnerable to skin diseases and medications (especially copper treatments must be dosed at half concentration). Can jump out of the tank if frightened.