Bicolor blenny

Bicolor Blenny Care: Ecsenius bicolor

The bicolor blenny (Ecsenius bicolor) won’t surprise anyone regarding names. With a clear line down the middle, you get two delightful colors for the price of one! But bicolor blennies are more than just another pretty face. With their habit of snacking on algae in a saltwater aquarium, they also earn their keep. (Talk about form AND function!)

Table of Contents: Bicolor Blenny Care

While the bicolor blenny isn’t too difficult when it comes to care and management, you may want to read through the entire article. They have a few little notes you’ll need to know about. But if you’re going to skip through the links to find a specific piece of information? We’ve got you covered, too.

Quick Facts

  • Common Names: Bicolor blenny, bicolored blenny, Two-colored blenny, Flame tail blenny
  • Scientific Names: Ecsenius bicolor
  • Size: 4 inches (10.2cm)
  • Minimum Tank Size: 30 Gallons (114L)
  • Reef Safe? With Caution
  • Care or Experience Level: Easy
  • Preferred Diet: Herbivore
  • Original Part of the World: Indo-Pacific

Bicolor blenny in lighter coloration

Description of the Bicolor Blenny

It isn’t difficult to figure out how the bicolor blenny earned its name. The front half of this little fish ranges in color from brown to blue. And the back? It’s a bright orange-yellow. The slim, eel-like silhouette makes for a striking look that stands out in a reef tank nicely. And, of course, how can anyone resist the cirri that stand out above their bulging eyes? They’re cute little aliens, hopping from rock to rock in search of the next patch of algae.

Male bicolors undergo color changes throughout their lives. During the spawning season, the anterior (front) half turns a vibrant blue to attract females. And while both sexes have a continuous dorsal fin, it extends a bit further down the tail in males. If you take a closer peek, you’ll also note thicker “lips” on their faces. Considering they’re smaller fish, though, that might require a magnifying glass (and a patient specimen).

The bicolor blenny belongs to the Bleniidae family or the “comb-tooth” blennies. Inside their jaws, you’ll find tiny rows of teeth with comb-like projections. The design helps strip algae away from rocks and corals. And it makes them the perfect additions to any marine tank with random patches of this particular aquarium pest.

Bicolor Blenny Lifespan

The bicolor blenny inhabits reefs throughout the Indo-Pacific. These colorful aliens frequent lagoons, hugging the seaward side along the rocks. Divers and snorkelers can see those bright faces popping out of crevices in and around the rocks.

Unhappily, they aren’t the most camouflaged fish on the reef. As such, they don’t have a great lifespan in the wild: only around 2-4 years. But in captivity, you can see them live for up to 10 years, with proper care. (It’s amazing what can happen when you’re not ducking out of sight of predators all the time)

Creating the Ideal Bicolor World

While the bicolor blenny shows up throughout the Indo-Pacific region, your best bet of seeing them is around Maldives, Samoa, the Ryukyu Islands, Phoenix Island, Micronesia, and down to the Great Barrier Reef. As they graze, they duck in and out of crevices. The narrow confines of the rock and coral provide a natural, safe harbor for the fish. (Not to mention some of the tastiest habitats for that algae growth)

And you’ll need to provide the same shelter. Live rock works nicely as it allows for the natural caves and ledges bicolor blennies need for exploration and hiding. And the more porous your rocks? (In other words, the greater the number of holes) The better your bicolors will do. These blennies usually choose one cave as a frequent haunt. But they’ll need more than one to choose from when you first introduce them to your reef tank.

As bicolors feed on algae, you want to opt for mature live rock – not a fresh piece of dry rock. In a new “sterile” tank without a functional ecosystem, your bicolor blenny can end up starving. You want a healthy crop of algae already attached to the structures in the tank. (I know, it sounds crazy to WANT algae in an aquarium, but these fish are particular)

Ensure the rock you choose is supported well, too. Bicolor blennies aren’t above digging around in the sand. As they move rubble and shells in their search for food, you don’t want them to accidentally topple the rock on their heads. If need be, epoxy the rock pieces together.

The bicolor blenny needs plenty of rockwork

Bicolor Blenny Tank Size

The bicolor blenny isn’t big in the size department. Nor do they engage much in open swimming throughout a tank, preferring to explore the rockwork. But they’re NOT ideal choices for nano aquariums. As space goes down, their aggression goes UP. And you don’t want your cute little alien to lose its manners. So don’t go any smaller than 30 gallons (114L).

You CAN crowd more rock structures into a bicolor blenny tank than you would with another species. They’re going to hop and scoot from perch to perch in favor of swimming. Of course, if you plan to set up a community, you’ll need to consider your other fish. But an obstacle course? Your bicolors will love it.

A tight-fitting lid is an absolute MUST when it comes to aquariums with a bicolor blenny, though. They’re small, delicious, and, therefore, possessing fantastic flight reflexes. This puts them into the category of “carpet surfing” fish. The last thing you want to do is come home and find a colorful fish gasping on the floor. (Or, worse, NOT gasping) They may not be interested in swimming, but they get pretty high in the tank as they bound from rock to rock. Don’t take a risk on something spooking them into darting for the surface.

Are Bicolor Blennies Reef-Safe?

Technically, the bicolor blenny is considered reef-safe. They’re herbivores, and they’re only interested in snacking on algae – not coral. But there’s a line of caution you’ll need to keep in mind. If your bicolor isn’t appropriately fed (we’ll get to that in a minute), or you attempt to crowd them? They can forget their manners and turn into problems.

A hungry (or irritated) bicolor blenny can pick at large polyp stony (LPS) corals or the mantles of tridacnid clams. Even a happy, healthy blenny may do so as part of a natural foraging trip if the algae bloom close to these groups. The comb teeth won’t hurt either species, but the activity WILL cause them to retract their polyps/tissue. And depending on how long your bicolor hangs out in the area? You can start to see stress or even starvation.

So while the species IS reef-safe, you need to pay attention to what’s going on in your tank. This may mean increasing your feeding schedule, planting a separate algae patch (never thought you’d ADD algae to a tank, did you?), or thinning your stock.

Bicolor Blenny Diet

One of the best aspects of the bicolor blenny is their herbivore menu. They LOVE algae. Devouring the microalgae that sprouts on the live rock and other hard surfaces in a marine tank provides a healthy cleaning operation for aquarists. It’s the perfect relationship.

Or it is until you realize that WITHOUT algae, your bicolor blenny WILL die. But you also can’t expect your little alien to ONLY survive on algae. (So if you picked one up hoping it could control your algae problem, you’re in for a shock) It’s a careful balancing act.

You want to make sure your bicolor always has access to at least SOME algae. And live rock? That does the trick. If you’re worried about having enough, a little “garden” of algae in the corner of your tank will do the trick. But you still need to provide supplements like seaweed or commercial foods with a marine algae base to round out a healthy bicolor diet.

And you should still offer the occasional protein source. After all, you want those vibrant colors to continue to stand out in your reef tank. Bicolor blennies will accept frozen, freeze-dried, or live brine or mysis shrimp or krill, provided you chop the pieces small enough. (Don’t forget: tiny fish equate to tiny mouths)

They’re active fish, conducting their grazing habits throughout the daylight hours. So you want to make sure you offer them food twice a day. That will meet their metabolic needs.

Bicolors are usually shy

Bicolor Blenny Behavior and Tank Mates

The bicolor blenny is a reasonably happy fish – under the right conditions. It’s when you go out of their “comfort zone” that you start to see the dark side come out. (No lightsabers, though – they’re not THAT cool)

They DON’T like sharing tank space with other bicolors. The only exception is if you come across a bonded male-female pair. And those are difficult to track down. As such, you’re better off housing a single bicolor blenny.

Unfortunately, the problems don’t end there. They don’t like ANY fish that enjoys algae. It’s competition, and they aren’t about to share. They’ll pick on other blennies, gobies (especially if they’re small enough to get bullied), and dartfish. And while bicolors don’t attempt to harass them, you need to avoid seahorses, too. The two species share the same menu, and delicate seahorses can’t move as fast as the blennies and end up starving.

You also can’t stock fish that LOOK similar since bicolors aren’t smart enough to tell the difference. So you need to avoid mixing them with royal grammas and bicolor pseudochromis.

But that still leaves you with plenty of options for tank mates. Since they’re herbivores, they’ll leave your crustaceans alone. And they don’t have any problems with the following tank mates:

  • Boxfish
  • Butterflyfish
  • Chromis
  • Damselfish
  • Pufferfish
  • Tangs

Of course, you need to consider the predator side of the equation. The bicolor blenny ISN’T a big fish. And they often end up as snacks for plenty of fish out on the reef. If you DO have an impressive community tank with any of these fish, make sure you provide extra hiding places and crevices to keep your bicolors safe:

Breeding the Bicolor Blenny

It’s relatively simple to sort male and female bicolor blennies apart. They both have the same color pattern, but females show a little less orange. And if you take a look at the anal fins? Males possess “egg spots.” These are egg-shaped marks on the large, pointed fin.

Of course, if you’re hoping to breed bicolor blennies, you’ll need to get your hands on a bonded pair. Otherwise, you’re in for some extra work while the two learn to live with each other. You’ll often see fighting occur – and it can get difficult to tell actual fighting from the “courting” ritual that precedes spawning. (The two encounters look remarkably similar)

The bicolor blenny lays eggs in nooks and crannies and guards the nest. And that applies whether they’re in the wild or an aquarium. So, again, it’s crucial to provide porous live rock throughout your tank. This will give your pair plenty of choices for their nesting site.

The male and female come together in “battle” before retiring to their chosen spot. They’ll remain around the nest for several days until the eggs hatch. That’s the easy part (mainly because the parents do all of the work). Attempting to rescue the fry and raise them? That’s tricky. You need to transfer them to prevent another fish from having the fry as a snack. And you’ll need to provide the proper size food (rotifers work best). All while performing 10% daily water changes to maintain proper water quality.

Unfortunately, most bicolor blenny fry don’t survive. If you want to breed your super-cute aliens? Make sure you’re prepared ahead of time for the time and work.

The male bicolor blenny has egg spots on the anal fin

Pros and Cons

The bicolor blenny is undeniably adorable. They’re also extremely active in a reef aquarium, drawing the attention and awe of aquarists at every level. But you need to weigh a few positives and negatives before you bring one home:


  • Bicolor blennies feed on algae throughout a tank, keeping things clean.
  • As they’re not active swimmers, you can fill your aquarium with more rock structures.
  • The bicolor blenny is reef-safe when provided with a healthy diet and enough space (and proper tank mates).


  • The bicolor blenny often gets stressed (when transported, by improper acclimation, or when water quality drops), resulting in disease.
  • Without SOME algae in the diet, your blenny can die.
  • While a generally peaceful fish, the bicolor blenny won’t tolerate other bicolors, fish similar in appearance, OR fish that also feed on algae.

For More Information

Hopping, colorful aliens? Who doesn’t want one bouncing around their saltwater aquarium! The bicolor blenny is the perfect addition for anyone’s tank. And this information should seal the deal (as if you could be on the fence after getting a peek at these fish).

This YouTube video shows a bicolor blenny zooming around a tank:

Want to know about some of the best bicolor blenny tank mates?

Sure, the bicolor’s cute. But maybe you’re interested in other blennies. No problem:


The bicolor blenny draws people in with their striking division of blue and orange. And then you get a glimpse of that face. Or maybe you saw them hopping around an aquarium in a fish store. And then you find out they LOVE algae, helping to clean up a tank. And you can’t wait to add them to your marine tank. Provided you meet their dietary needs, you’re in the clear. Just don’t try to double-down on algae-eaters, or you could find yourself with problems.


  • Allen, G.R. 1997. Marine Fishes of Tropical Australia and Southeast Asia.
  • Froese, R. and Pauly, D. 2005. “Ecsenius bicolor.” FishBase.
  • Michael, S.W. 2001. Marine Fishes, 500+ Essential to Know Aquarium Species.
  • Randall, J.E., Allen, G.R., and Steene, R.C. 1997. Fishes of the Great Barrier Reef and Coral Sea.





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