Bicolor Blenny (Ecsenius bicolor): Ultimate Care Guide

Native to Fiji, Indonesia and Sri Lanka, the Bicolor Blenny is a great algae eating fish that will add a splash of color to your aquarium. This fish features a brown or blue colored front half, fading to yellow-orange beyond the midsection. Although mainly an algae eater, the Bicolor Blenny will also consume a range of prepared meaty foods. It is important to keep this fish well fed to prevent aggression against tank mates, including corals. Normally considered reef safe, this species wants lots of space and live rock to hide, perch and graze on. Without enough food or space, hobbyists can see problems with tank mates and violence against certain corals.

With its environmental and nutritional needs met, the Bicolor Blenny is a great tank addition which can help keep algae in check. Although similar to other Blennies, this species has certain differences that hobbyists should be aware of. Let’s take a look at what you’ll need to succeed with this colorful and useful aquarium fish!

Are Bicolor Blenny Reef Safe?

Bicolor Blenny are often reef safe but this requires enough food, space and live rock. This species can attack certain corals and clams if it’s hungry or feeling cramped. Because this fish is known as an algae eater, some hobbyists might think grazing can satisfy all of its nutritional needs. This is only the case in large aquariums with lots of live rock. In most hobbyist aquariums, this species will need added feeding with prepared meaty foods and vegetable matter.

Bicolor Blenny Care

Bicolor Blenny are a hardy aquarium addition. Care must be taken to keep them well fed and ensure enough tank space and live rock. This species is not suitable for micro aquariums; the minimum tank size needed is 30 gallons.


Bicolor Blenny prefer water temperatures in a range of 72° – 78° F.

Water pH

Bicolor Blenny expect water alkalinity in a range between 8.1 and 8.4 pH.

Bicolor Blenny (Ecsenius bicolor)
Bicolor Blenny (Ecsenius bicolor)

Bicolor Blenny Size

Bicolor Blennys will reach a maximum size of 4 inches.

Food & Diet

Bicolor Blenny prefer to eat algae and vegetable material but can eat a range of prepared meaty and vegetable foods. Many aquariums won’t have enough algae growth to satisfy this species’ nutritional needs. Plan to supplement your Bicolor’s diet with prepared vegetable and meaty foods. Frozen foods containing algae, or algae pellets, are an excellent supplemental food source. You may have a challenge getting your Bicolor Blenny to recognize prepared foods as foods. Once they are initially coaxed them to bite on prepared foods, they should start feeding reliably.

It needs to be stressed that Bicolor Blennys shouldn’t eat too much meaty foods. Algae, both from live rock grazing and prepared, should form the basis of their diet. Inadequate vegetable foods can result in subdued coloration.

Do Bicolor Blenny eat algae?

Bicolor Blenny eat algae from live rock and tank surfaces; also from prepared algae-containing foods. Be sure your tank has enough algae growth to support this species. When adding A Bicolor to a new aquarium it is best to acclimate them to prepared foods early so you’ll have a nutritional backup if they consume all available tank algae. Hungry Bicolor Blennys can be aggressive and may attack other tank mates including clams and some corals.

Bicolor Blenny Lifespan

Bicolor Blennys will live up to 4 years in an aquarium. Expect most to have a lifespan of around 2 years.

Bicolor Blenny Tank Size

Bicolor Blenny need a minimum tank size of 30 gallons. This species is not suitable for micro aquariums. Although not a large fish, they do best when given large tank volume and lots of live rock. Cramped environments can cause your Bicolor stress and increase their chances of attacking tank mates.

Unless you have an exceptionally large tank, don’t try to keep two Bicolor Blennys together. Bicolors don’t get along with other members of the same species–unless part of a mated pair. In fact, this species can have issues with any other algae eaters, or fish they decide are competition for food.

Tank Setup

Bicolor Blennys want lots of live rock with hiding spots. This species needs mature tanks with functioning ecosystems as they’re algae eaters. Plan for at least a 30 gallon aquarium. Smaller tanks will create stress and raise aggression.

A deep sand bed isn’t required. While Bicolor Blennys are algae eaters, they aren’t sand sifters like Gobys. They may dig and move sand but mostly they will hide in, and graze on, live rock. Live rock and other hardscape should be placed in your aquarium before sand. This will keep sand movement from dislodging anything that can result in injuries. Ensure your tank has a sturdy and tight-fitting lid. This species is a known jumpers and will escape any tank that isn’t well covered.

Many aquariums will not provide enough algae to keep Bicolor Blennys well fed. Most hobbyists supplement their Bicolor’s diet with prepared foods that contain algae. Another alternative is to maintain a refugium where edible algae can be cultivated. A refugium can also add more copepods and other microfauna to your tank’s environment. If you are building a community tank, a functioning refugium can provide algae and microfauna for a range of fish besides Bicolor Blennys.

Breeding Behavior of Bicolor Blenny

Most Bicolor Blenny available to hobbyists have been caught in the wild. Breeding this species is difficult but can be easier if you have a mated pair. Bicolors don’t get along with other fish of the same species, so it will be hard to take just any male and any female and have them breed. When juvenile this species will pair up with a member of the opposite sex and will tolerate and breed with this mate. If you are able to get such a breeding pair you’ll be halfway to Bicolor Blenny breeding success!

During breeding, Bicolor Blennys go through extreme coloration changes. The male’s blue coloration will become much brighter, sometimes spreading across the entire body and replacing the yellow-orange tint on their back half. Females will become black and both sexes will develop white stripes. Bicolor courtship resembles fighting. The female will grow large with eggs and they will mate in the male’s “nest.” These eggs will hatch in around 8 days.

It is important to separate the newly free-swimming fry and transfer them to another tank. Bicolor Blenny fry are a tasty snack and won’t survive long with other tank inhabitants. This separate tank will need frequent water changes as the fry need regular feeding with phytoplankton, also known as “green water”, and rotifers. When planning on rearing Bicolor fry make sure you have a good source of phytoplankton and rotifers. This often means culturing your own. Eventually the fry will being eating algae and can be transferred to another tank when around ½ inch in length.

Bicolor Blenny Male or Female

It can be difficult to sex Bicolor Blenny when they are not actively breeding. Males will generally have more intense coloration with a brighter blue front half. Female’s coloration will be more subdued, the front half seen as a duller blue to brown. During breeding, sex becomes obvious: males develop intense coloration with brighter blue and orange. Females will turn darker, even black, and both sexes will develop white stripes.


Bicolor Blenny are hardy fish but can be susceptible to Ich and Marine Velvet. Always keep new tank additions in a quarantine tank (QT) for 8 weeks before adding to your display aquarium. Ich can be visible as white spots and Marine Velvet as a dusty brownish-gold color. Both diseases are fatal without treatment.

Maintaining a QT is also critical for applying medicine or special treatments to your Bicolor Blenny. Many medications used for common marine fish diseases should only be applied to the infected fish and not broadcast throughout your display tank. Some medications, particularly those with a copper base, are lethal to many reef tank inhabitants.

Bicolor Blenny Tank Mates

Bicolor Blenny are often docile and will only have problems with members of the same species. Every fish has it’s own personality and Bicolors are known to sometimes attack or harass other algae eating fish they view as competition for food.

Are Bicolor Blenny Aggressive?

Bicolor Blenny can be aggressive if they are underfed or aren’t provided with enough space and live rock. A hungry Bicolor Blenny can be aggressive against corals, clams and other tank mates. To ensure the best behavior from your Bicolor Blenny, ensure they have enough space and lots of live rock to hide in. Also make sure enough food is provided and that your Bicolor is eating.

Examples of Compatible and Incompatible Tank Mates

A well fed Bicolor Blenny will get along with most fish except those of the same species. They may harass smaller algae eating fish like Seahorses. Gobies and Dartfish may be a target if your Bicolor becomes aggressive. Tangs are tough and fast enough to make good tank mates.

Where can I find Bicolor Blenny for sale?

Bicolor Blenny are popular marine aquarium fish and should be available from your local fish store or Internet sources.

Bicolor Blenny Price

Bicolor Blenny are priced by size. Small specimens can be bought for around $30 USD. Larger fish can cost up to $80 USD.

Leave a Comment

Your email address will not be published. Required fields are marked *