Bicolor Blenny
Ecsenius bicolor
Two-toned charmer with a big personalityBeginner
- Lifespan
- 4-6 years
- Size
- 8-10cm (3-4in)
- Social needs
- One per tank unless a bonded pair
- Time
- Low
- Cost
- Medium
- Diet
- Omnivore, algae-leaning
Overview
What is this animal?
- The Bicolor Blenny is a hardy, comical fish, dusky blue at the front and orange at the back, with expressive eyes and a habit of perching and peeking from rocks.
- Its personality and toughness make it a popular beginner marine.
- It is reef-safe and helps graze film algae, though it needs supplemental feeding once natural algae thins.
- Easy to keep and full of character, it suits new and experienced reef keepers alike.
Temperament
- Generally peaceful but territorial toward other blennies and sometimes similar small fish, occasionally nipping at tankmates that invade its space.
- Keep one per tank unless you have a bonded pair.
- It is reef-safe with corals and invertebrates, though the rare individual may nip coral polyps if underfed.
- Mostly it is an entertaining, characterful fish that perches openly and interacts with its keeper.
A good fit for
- Beginners wanting a hardy, characterful fish
- Reef tanks with film algae to graze
- Keepers who will supplement with nori
- Peaceful community reef systems
Common mistakes to avoid
- Starves in tanks lacking enough algae
- Known jumper; needs a secure lid
- Two blennies together usually fight
- Rare underfed individuals may nip corals
Enclosure
Minimum 110 litres (29 US gallons)
Must be housed alone. One per tank unless a bonded pair
- House in a reef tank of at least 110L (30 gallons) with plenty of live rock providing algae, perches, and a hole or crevice it can claim as a home base.
- A mature tank with algae film suits it well.
- Maintain temperature 24-27C (75-81F), salinity 1.024-1.026, pH 8.1-8.4, and ammonia and nitrite at zero.
- A secure rock retreat gives this perching fish confidence and frequent visibility.
Supplies
Setup
- Tank, stand and sump
- Return pump and powerheads
- Protein skimmer
- Reef lighting
- Rock and sand
- Salt mix, refractometer and test kits
- Quarantine tank
Ongoing
- Dried marine algae (nori) sheets
- Magnetic or suction veg clip
- Spirulina flake and algae pellets
- Frozen mysis shrimp
- Frozen enriched brine shrimp
- Marine flake or small pellet
- Small thawing cup and strainer
Safe substrate: Aragonite sand · Dry or cured live rock · Bare bottom
Care routine
Daily
- Check salinity, temperature and flow
- Feed
- Head-count and look everyone over
- Top up evaporation with fresh water
Weekly
- Offer nori on a clipevery 2 days
- Service the skimmer and filter socksevery 3 days
- Check the belly profile
- Clean the glass
- Test the water
Monthly
- Water changeevery 2 weeks
- Calibrate the refractometer
- Check salt, RO/DI and reagents
Less often
- Deep-clean pumps and powerheadsevery 3 months
- Replace RO/DI filter mediaevery 6 months
Vet: Quarterly belly-profile review — every 3 months
Top resources for more info
Independent creators and organisations we would send a friend to. We have no affiliation with any of them, and nothing here is sponsored. Links checked 2026-09-19.
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Diet
- An algae-leaning omnivore that grazes film algae and diatoms but also takes meaty foods.
- Offer dried nori, spirulina flakes, algae pellets, and frozen mysis and brine shrimp one to two times daily.
- A varied diet weighted toward vegetable matter keeps it healthy and reduces any temptation to nip corals.
- Supplement well once natural tank algae is grazed down to prevent a hollow belly.
Health
- Hardy and disease-resistant relative to many marine fish, though quarantine and stable water are still sensible.
- Most losses come from starvation in algae-poor tanks or from jumping rather than from illness.
- Watch the belly profile and appetite; a pinched stomach signals the need for more food.
- Provide a secure lid, as bicolor blennies are capable jumpers given any open gap.
Is your enclosure big enough?
Is this urgent?
In a reef, stability matters more than any single target number. A parameter moving fast does more damage than a parameter sitting slightly off.
Go now
Today
Quarantine every new animal, including corals and inverts. It is the single practice that separates a reef that lasts from a reef that restarts.
This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it — and the time to find one is before you need one.
What it really costs
Setup, monthly, first year and across a whole life, itemised and with the electricity worked out from the actual wattage. Published figures for the same animal disagree by a factor of four, so the calculator shows ranges rather than picking one.
Bedding and substrate
In a marine system the rock and the sand are life support, and how you start them decides the first six months.
Safe
With a caveat
Never
This is our general list for saltwater fish. We have not built one specific to Blennies yet.
My kit says 0.25 ppm. Is that dangerous?
A liquid kit measures total ammonia, but only the un-ionised fraction is really toxic, and that fraction is governed by pH and temperature — each whole pH unit multiplies it roughly tenfold. So the same reading can be nearly harmless in one tank and lethal in another; this works out which one you are in.
Compare with other animals
The same axes for every animal, side by side — the way the guides are written makes that a fair comparison rather than two articles.
Blennies, side by side
Same axes, same care guides — the honest way to choose between types.
See all Blennies side by side →
