Temp
Food
Flow
Difficulty
The Bicolour Blenny (Ecsenius bicolor) is one of those charming little fish that adds both function and personality to your marine aquarium. With its half-orange, half-blue body and ever-watchful eyes, the Bicolour Blenny is as entertaining as it is useful. It’s a brilliant choice for those looking to control algae growth while enjoying a fish that’s full of quirky behaviour.
Despite its small size, this blenny has a big personality. It loves to perch on rocks, poke its head out of crevices, and interact with its environment—and occasionally, its owner! In this care guide, we’ll explore everything you need to know about keeping a happy, healthy Bicolour Blenny in your saltwater tank.
Enter Your email to be sent this care guide
Getting to Know the Bicolour Blenny
Native to the Indo-Pacific, the Bicolour Blenny is a small, reef-safe herbivore that grows to around 10–11 cm (4 inches). It’s best known for its distinctive colouring—typically a dark blue or brown front half fading into a bright orange tail—and its comical facial expressions.
Blennies are bottom dwellers and will spend much of their time perched on rocks or hopping between hiding spots. They’re perfect for medium-sized reef setups and are generally peaceful, although they can be territorial with similar species.
Tank Requirements
The Bicolour Blenny isn’t overly demanding, but it does need a well-maintained environment with plenty of rockwork to graze on and explore.
Minimum tank size: 80–100 litres (roughly 25–30 gallons)
Aquascaping: Provide live rock for grazing, hiding, and perching
Substrate: Sand or fine gravel is preferred
Tank lid: Strongly recommended—blennies are known to jump
These fish are best introduced into a mature tank, where natural algae growth is already established.
Ideal Water Conditions
Stable water quality is key to keeping your Bicolour Blenny healthy and active. They’re quite hardy but still benefit from routine maintenance and consistent parameters.
Temperature: 24–26°C
pH: 8.1–8.4
Salinity: 1.023–1.025
Ammonia/Nitrite: 0 ppm
Nitrate: <10 ppm
Carry out regular water changes and monitor levels weekly to ensure a stable environment.
Diet and Feeding
In the wild, Bicolour Blennies are dedicated algae grazers, helping to keep reef surfaces clean. In a home aquarium, they’ll do the same, but may need dietary supplements, especially in cleaner or newer tanks where algae is limited.
Offer them:
Nori (seaweed) clipped to the glass or rocks
Spirulina-based flakes and pellets
Algae wafers
Occasional mysis or brine shrimp (treat only)
Feed once or twice daily, depending on how much algae is naturally available in your tank. A well-fed blenny will appear plump and active.
Behaviour and Tank Mates
Bicolour Blennies are generally peaceful and can be kept with a wide range of reef-safe species. However, they can be territorial toward other blennies or similar-looking fish, especially in smaller tanks.
Good companions include:
Clownfish
Gobies
Tangs
Firefish
Cleaner shrimp and peaceful inverts
Avoid aggressive or overly boisterous tank mates, as blennies may become stressed or outcompeted for food.
Reef Compatibility
The Bicolour Blenny is considered reef-safe, with the occasional exception of nipping at SPS or clam mantles if they’re underfed. As long as they’re getting enough algae or plant-based food, they’ll leave corals alone and happily contribute to a healthy reef environment.
Final Thoughts
The Bicolour Blenny is a delightful little addition to any reef tank. It brings together good looks, practical algae control, and a surprising amount of personality. They’re hardy, easy to care for, and endlessly fun to watch as they go about their day perched like little sentries on your live rock.
Perfect for intermediate aquarists and suitable even for some beginners, the Bicolour Blenny is a small fish with a lot to offer—just make sure they’ve got algae to nibble and places to call home.
