Bicolor Blenny
Ecsenius bicolor
Type: saltwater, reef fish, benthic
Physical Characteristics
Elongated, cylindrical body; the front half is deep bluish-purple or neon blue while the rear half is bright orange to yellow. It has prominent cirri (antenna-like growths) above the eyes and a continuous dorsal fin. Mouth is located ventrally for scraping algae.
Habitat & Distribution
Inhabits coral reefs and rocky areas in the Indo-Pacific, from the Maldives to the Great Barrier Reef and Micronesia. Found at depths of 1 to 25 meters, often residing in abandoned worm holes or small crevices.
Size & Weight
Typically ranges from 3.5 to 10 centimeters in length. Maximum recorded size is approximately 11 centimeters. Weight is negligible due to small size.
Similar Looking Species
Blackline Blenny (Meiacanthus nigrolineatus) which has different color patterns, or the Tailspot Blenny (Ecsenius gravieri) which lacks the distinct two-tone horizontal split.
Ecological Role
Primarily a herbivore that controls algae growth on reefs; also serves as a prey species for larger reef predators.
Diet
Primarily herbivorous, feeding on filamentous algae and detritus by scraping it off rocks and coral surfaces.
Behavior
Solitary and highly territorial fish. They are diurnal and spend most of their time perched on coral or retreating into small holes, darting out quickly to feed.
Reproduction
Known to be egg-layers. The female deposits adhesive eggs in a sheltered crevice, which are then guarded and aerated by the male until they hatch into planktonic larvae.
Conservation Status
Least Concern (IUCN); populations are currently stable across their wide geographic range.
Identification Tips
Look for a fish with a striking head-halves contrast (blue/purple front and orange back) poking its head out of a hole or perched on a coral head using its pelvic fins like tiny legs.
Interesting Facts
Depending on their mood or environment, bicolor blennies can display three color phases: the standard bicolor, an all-black phase, or a striped phase with a dark back and pale underside.
Identified on: 6/16/2026
Mode: Standard