Blennies love swimming near the bottom of the aquarium. This blue and yellow Blenny is swimming next to coral

Blennies are saltwater fish native to islands in the Pacific Ocean. They are commonly found in tropical regions, and are usually kept in community tanks. They are known for their beautiful colors and patterns.

Blennies are herbivores, only eating plant matter. They are also very easy to feed, eating a wide variety of foods including flakes and pellets.

Blennies are very easy to care for, and don’t require much maintenance. They are very friendly and sociable, and will adapt well in a community tank. 

They are very colorful, and will look stunning in your tank. You can start adding them to an existing tank right now, and they will adjust to their new environment quickly. 

Blennies are one of the most interesting saltwater fish. Reef aquarium owners tend to shy away from these fish, because they’re not as common as clownfish and gobies. But many people are unaware that blennies are actually great fish for a family saltwater aquarium, especially a smaller aquarium. 

Blennies are a type of fish that can be found in tropical and subtropical waters. They’re small fish, usually between 2 and 3 inches, so they’re perfect for a nano reef or a 15-gallon aquarium.  They’re also colorful fish, making them a great addition to a dull or under-decorated aquarium.  The only downside is that they’re not as common as more well known saltwater fish.

Blennies Information

  • Average length: 1 – 5 inches depending on variety
  • Scale Type: Most Blennies have scaleless bodies
  • Fish Colors: Blue, black, white, gray, yellow, and orange
  • Tolerance to Heat and Cold: Not cold
  • Good Pet: Yes
  • Good with Other Blennies: Moderate
  • Good with Other fish species: Only peaceful ones
  • Good for Less Experienced Pet Owners: Yes
  • Health Concerns: They tend to have fin rot, Marine Velvet Disease, and Marine White Spot Disease
  • Average Life Span: 2 to 6 years

Physical Appearance of Blennies

a blue and yellow Blenny swimming next to purple coral

To understand the physical appearance of Blennies, let’s look at the most common Blennies in family aquariums.

Bicolor Blenny

The Bicolor Blenny has a dark blue color on the front part of their body while the back end of their body towards their tail is orange. This type of Blenny is known for the males being larger than females. Bicolor Blennies do well in reef aquariums.

Two Spot Bimaculatus Blenny

The fish originates from the rocks and crevices of Cebu, Philippines. This Blenny has two spots near its stomach on the side of their body and that’s how they got their name. The Two Spot Bimaculatus Blenny has very large eyes that have a black stripe running through them.

Horned Blenny

This fish has a few colors that they’re known for. Some will have a dark body, others white, and some golden with brown spots on the body and fins. The fish have some unique horns that stick out from their head that look like antane on Shrimp.

Orange Spotted Blenny

Also known as Red Spotted Blenny, this fish has a white body with orange patches in places and orange to red polka dots all over their body.

Starry Blenny

This Blenny is also known as Snowflake Blenny and has a dark brown body with white spots that look like stars or snowflakes. The tail and pectoral fins of this Blenny are yellow.

Midas Blenny 

a golden colored blenny near the bottom of the aquarium

This Blenny is a golden yellow fish that has a narrower body that’s longer than most other Blennies. The fish has deep blue eyes and it swims like an eel. They do well in a reef aquarium.

Horseface Blenny

Also known as Red Lip Blenny, this fish has a body that’s mustard to dark brown with some red and yellow markings on their body. The face of the fish looks like that of a horse with a blunt nose and red lips. The head of this Blenny has four small horns.

Yellowtail Fang Blenny

They are also called a Forktail Blenny because their tail resembles a fork with two long spines at each end and five short spines in the middle. The front of the fish’s body is pale blue but transitions to yellow about the middle of their body.

Canary Blenny

This Blenny is yellow with a tail that looks like a fork. They are also known by the name Oualan Forktail Blenny and the males are larger than females. The males also tend to change their colors spontaneously during the mating season to attract the females.

Black Sailfin Blenny

This fish has a black body with equally dark fins. They love perching on live reefs and are known for eating on stubborn algae at the bottom of the tank.

Temperament of Blennies

Blennies love the security of the bottom of aquariums because there are a lot of places to hide

Blennies are generally a non aggressive fish that can live with other peaceful fish. They are a territorial fish that can fight over a mating partner or space. 

Battles between Blennies can become fatal and fish owners should eliminate all fight triggers by keeping a good ratio of males and females in a tank. One male for every three females is a good ratio.

Having enough space in the tank is also a vital consideration for your Blennies to avoid fights due to overcrowding.

As a general rule of thumb, avoid placing more than one Blenny species in a tank to avoid territorial fights. Fish from the same species of Blennies tend to fight a lot especially when there are more males in the tank.

Best Tank Mates for Blennies

Blennies are very small and should not be placed with larger fish that might prey on them. Fish such as the Lionfish, Bluefish, or weakfish may eat your Blennies. Here is a list of some fish that can live with Blennies peacefully.

Blennies from different sub-groups that don’t look similar can live together in one tank.

Tank Conditions for Blennies

Blennies can adapt to any marine aquarium with optimal water conditions and enough space to swim. Blennies normally dwell at the bottom of the tank. They love habitats with lots of rocks, crevices, and hollow caves they can hide in whenever they sense danger. 

Blennies blend in really well with plants and other things at the bottom of aquariums

Some Blennies like the Lawnmower are even known to burrow themselves into the substrate.

A tank with Blennies should be covered at the top because they are known to jump out.

The minimum tank size for a Blenny is about 20 gallons but some larger Blennies need bigger tanks of 30 gallons or more. A large tank is ideal because water conditions stay better longer than in smaller tanks. 

It’s important to have water testing kits to check that nitrite, nitrate, and ammonia levels remain at zero.

An aquarium filled with Blenny fish should have temperatures kept between 77 and 81 degrees Fahrenheit. Maintaining the pH of the water for your Blennies is also crucial for their health. For Blennies, the pH is best between 8.0 and 8.4. These levels can vary depending upon the specific Blenny species you have in your tank.

The pH of the water tends to fluctuate as your fish releases waste into it. You can regulate the pH by simply doing some water changes. If you find that it’s getting low it is possible to add a teaspoon of baking soda in a 20 gallon tank whenever needed.

Blennies feed on algae, if you want them to eat algae you’ll want to have enough light inside their tank. The light does not have to be too bright, just enough to replicate the natural sunlight. This will help promote the growth of algae inside your tank. 

Tank Maintenance

This blenny is hard to spot because they blend in with things in the aquarium

The tank will require regular cleaning as Blennies are a sensitive variety of fish. Around 25% of the water should be changed weekly.

The water levels should be regularly monitored. Any spikes in dissolved compounds in the water can be fatal for them. The level of calcium inside the tank should not exceed 430 ppm. This will also help maintain a stable nitrate and pH level inside their tank.

The tank should only have a very small amount of ammonia in the water. Anything more than traces of ammonia can be toxic for your fish. You can use an all round tester kit to monitor the level of compounds and temperature inside the tank. Regularly monitor the temperature and pH level of the water inside the tank.

Attention Requirements for Blennies

Blennies are low maintenance and good fish for beginners and experienced aquarists. They aren’t picky eaters and they’re resistant to diseases unless exposed to poor water conditions. 

Blennies aren’t messy fish and don’t contaminate the water as much as other fish are known to. Monthly water changes and regular cleaning to water filters takes much less time than other fish. 

Health Issues

Blenny fish may at times become ill especially if the quality of water in their tank deteriorates. With regular water changes and fish feed with good quality food, then the chance of diseases should be minimized. 

Here are some of the most common illnesses among Blennies.

Marine White Spot Disease

Marine Ich, also known as White Spot Disease, is a common parasitic disease that affects saltwater fish. It’s caused by the ciliate protozoan parasite and Cryptocaryon irritans, which attach themselves to a fish’s skin and gills.

Marine Ich is very contagious and can spread quickly through an aquarium. It’s often introduced into an aquarium through new fish or contaminated equipment. Poor water quality and stress can also weaken a fish’s immune system, making them more susceptible to the disease.

Symptoms of Marine Ich

Symptoms of Marine Ich include:

  • White spots on the skin and fins of infected fish
  • Rubbing against objects in the aquarium

As the disease progresses, fish can become lethargic and lose their appetite.

Marine Velvet Disease

Marine Velvet Disease, also known as Velvet Disease or Coral Fish Disease, is a parasitic infection that affects saltwater fish. It’s caused by the dinoflagellate called Amyloodinium ocellatum, which attaches itself to a fish’s skin, gills, and fins.

The first signs of Marine Velvet Disease are usually a yellowish-gold dusting or velvet-like film on the fish’s skin. As the infection progresses, affected fish can become lethargic, lose their appetite, and display rapid breathing or gasping for air. In severe cases, Marine Velvet Disease can be fatal.

Symptoms of Marine Velvet Disease

Symptoms of Marine Velvet Disease include:

  • Yellowish-gold dusting or velvet-like film on the fish’s skin
  • Lethargy
  • Appetite loss
  • Rapid breathing or gasping for air

In severe cases, affected fish can also develop open sores and have abnormal swimming behavior.

Fin Rot

Saltwater fish are prone to various diseases, and one of the most common ailments is fin rot. Fin rot is a bacterial infection that affects a fish’s fins, causing them to deteriorate and even fall off in severe cases. This condition can cause discomfort for fish and lead to further complications if left untreated.

The bacteria responsible for fin rot are opportunistic pathogens that thrive in poor water conditions, like low oxygen levels or high ammonia and nitrite levels. Stress can also be a contributing factor, because it weakens the fish’s immune system and makes them more susceptible to infections.

Feeding Blennies

a pile of colorful fish flakes

Some Blenny fish are carnivorous while others are herbivores and it’s important to understand what to feed your fish before leaving the pet store. 

The carnivorous Blennies can feed living or frozen foods such as bloodworms and small crustaceans. Blennies like the Canary eat meat. The carnivorous Blennies can be fed on flakes with high protein content for proper growth and health.

The herbivore Blennies are often underfed. They love grazing all day on fresh vegetables or algae growing in the tank. But often the plant materials growing in the tank are not enough for them to survive on. It is important that they have enough food to feed on throughout the day.

Some examples of herbivorous Blennies include the Lawnmower Blenny and the Bicolor Blenny. It’s also worth noting that all Blennies can be fed on fish flakes or pellets. For the herbivorous types, it is important that the flakes or pellets have a lot of ground vegetables, vitamins, and other essential nutrients. 

It’s also easy to tell what food your Blenny can eat by observing its behavior. The Blennies that eat vegetables prefer dwelling at the bottom of the tank grazing on vegetables or living vegetation in their tank. 

Some people even use some Blenny species as cleaner fish to deal with stubborn algae growth in their aquariums. 

Carnivorous Blennies like the Fang variety of Blennies mostly swim near the surface. Even with the knowledge of how the herbivorous and carnivorous Blenny fish behave, it’s important to talk with the breeder or pet store on what to feed your fish before taking it home.

Author Profile
A woman with curly hair holding a cat.
Contributing Author & Social Media Expert

Maryna is an animal expert that has had dozens of animals in her life over the years. She has never found an animal that she didn't love immediately. It seems like every year she finds kittens that have been abandoned by their mom and she nurses them to health and finds homes for them. She contributes her vast knowledge about animals and family pets to our website and we're forever grateful to have her working with us. She's also an amazing graphics designer and has designed all of the social media images that we use across all platforms.