Color Change, Diet, Tank Size and Lifespan



Hello there! If you’re thinking about getting a Lawnmower Blenny, you’ve come to the right place. The Blenny is a popular choice for saltwater aquariums. These fish are known for their cute and quirky personalities, as well as their ability to keep your tank clean, and did you know they can change colors depending on their mood? 

A Chameleon and a Lawnmower Blenny side to side
Both the Chameleon and the Lawnmower Blenny can change colors.

So, if you like Chameleons and have a saltwater tank, then you might want to add this fish to your aquarium. But before you bring one home, there are a few things you should keep in mind like breeding, tank mates, and more so let’s get started! 

Species Summary

Known scientifically as Salarias fasciatus, Lawnmower Blenny or Algae Blenny is a good-natured fish who peacefully inhabit saltwater tanks and display delightful behaviors. These personality-packed fish are also diligent cleaners who will keep algae growth in check.

They belong to a genus with 13 species. Members all possess similar comblike teeth, which they use to scour rock and other surfaces for biofilm and algae. Lawnmowers are one of the largest and least colorful of the group.

These fish are native to the Indian Ocean off the African coast, the Red Sea, the Great Barrier Reef, and the waters surrounding Samoa and Micronesia. They can be found at depths up to 260 feet but mostly stick to shallow reefs and lagoons. Lawnmowers’ name comes from their ability to graze on their habitat’s algae, clearing the area like a goat in a field.

Wild Algae Blennies prefer environments free of other fish, allowing them to slowly explore amid the shelter of rock, coral, and sea plants. They are generally docile but will nip other fish if they sense competition for food.

Author Note: Lawnmowers are relatively inexpensive but have a shorter lifespan than many other saltwater aquarium fish. Though they require consistent monitoring of their dietary intake, they are widely considered a solid starter fish for beginner aquarists.


These Lawnmower Blennies are subdued shades of tan, green, or gray, with darker stripes crossing their bodies. This banded appearance, known as cryptic coloration, helps them blend into the reef bottoms they comb for algae, masking them from potential predators.

The Lawnmower Blenny has an oversized head with what resembles a prominent brow. Bluish dots encircle their pronounced black eyes, which feature a white stripe. The eyes can move independently of one another, enabling the Blenny to observe the broadest possible area.

This species has a large mouth and blue or black dots across its head. Lawnmowers’ faces, eye shape, and spiny fins give them an almost reptilian appearance, like an iguana. Healthy Lawnmowers have round, full bellies.

These fish also experience a slow-acting lightening or darkening of the pigment on their bodies and within the patterns on their flanks as they settle into their new home. As your Blenny acclimates to its tank, the tones will shift to better hide it among the rock and substrate of your tank.

Author Note: Owners often note that the fish are so good at camouflage they sometimes hide in plain sight. These scaled fish also experience color change based on mood. So once your Blenny is an established tank resident, changes in its shading can signal stress or health problems.

Beyond their lizard-like appearance, Lawnmowers have banded or beaded patterning that covers their entire body, including the fins. Based on this appearance, they are sometimes called Jeweled Blennies.

The fish’s wide mouths contain comblike teeth set in a flexible jaw. This unique structure enhances their ability to scrape surfaces and capture algae.

Lawnmowers have fanlike fins which help them navigate the rocks and craggy areas that make up their feeding grounds. While not as colorful as the typical tropical reef fish, Lawnmowers’ unique patterns and exaggerated anatomy make them stand out in your tank.

These fish have elongated dorsal fins that run the length of their bodies and broad pectoral fins. These structures give Lawnmower Blennies the nickname Sailfin Blenny. They also have appendages, called cirri, on top of their heads, between the eyes, that resemble skin tags or antennae. Rather than serving a biological function, they are additional camouflage that helps the Blenny blend in with the plants on the reef floor or lagoon bottom.


The Lawnmower Blenny has an average lifespan of 2 to 5 years. They are hardy fish that usually do well in tanks. Vigilant monitoring is essential to ensure they eat enough.

Average Size

The average size of a Lawnmower Blennies is about 5 inches, but adults can range from 4 to 6 inches. Their nutrition and overall well-being influence the size they reach.

Lawnmower Blenny Care

Lawnmower Blennies do best in well-established tanks with ample live rock and algae sources. They are industrious bottom-dwellers who withdraw when larger or aggressive fishes encroach on their space. Experts recommend introducing Lawnmowers to tanks that are at least one year old.

Your Blenny will be wild-caught. An established tank maximizes the chances of filamentous algae being present. This familiar food source will make your Lawnmower’s transition to tank life smoother. Ideally, they will feast on the algae and slowly grow accustomed to provided food and the other tiny organisms living in your tank.

Tank Size

Experts recommend a minimum tank size of 55-gallons for a single Lawnmower Blenny. A pair requires a 100-gallon or larger tank. While Lawnmowers are not active swimmers, they need ample room to graze for algae as they scour rocks and other surfaces. As with most fish, the bigger the tank, the better. These fish prefer moderate to high water movement because it oxygenates the water more effectively.

Water Parameters

  • Water temperature: 72 to 78°F
  • pH levels: 8.1 to 8.4
  • Water hardness: 8 to 12 dKH
  • Specific gravity: 1.020 to 1.025 sg

What To Put In Their Tank

Lawnmowers do best in tanks with live rock because it simulates nature. These conditions create prime surfaces for algae growth and homes for some tiny organisms the Blenny will also eat. A sand or coral sand substrate is ideal because the smoothness of the grain minimizes friction and resulting abrasions that your bottom-dwelling fish could sustain.

Author Note: When laying out the tank, space the rock wide enough apart so that your fish has plenty of hiding spots and room to explore. Artificial decorations are acceptable but do not overcrowd the tank floor.

Live plants are also ideal. Your Blenny will swim around them, and they provide another surface for algae growth. Be sure to select saltwater species that can grow in sand, including java moss, java fern, and cryptocoryne. You can also anchor seaweed into the substrate for your Blenny to eat. Avoid pointy plants or ones that your Blenny could get tangled in.

The Lawnmower will spend its time in the bottom third of your tank. In many cases, natural light is all they need. However, if your tank is in a shaded area or you have live plants, follow recommended lighting practices to ensure they experience proper conditions.

Is the Lawnmower Blenny Reef Safe?

Yes! The Lawnmower Blenny is reef sage and will comb the rocks searching for algae but won’t intentionally disturb or harm your coral. However, stressed or starving Lawnmowers may bite at coral polyps. Be sure to look out for this aggressive behavior and increase your Blenny’s feedings accordingly.

Common Possible Diseases

Marine Ich, a parasitic infection, is the most common disease affecting Lawnmowers. Fish develop the disease from Cryptocaryon irritans, an organism that grows in tanks with poor water conditions. You can spot the infection by the white spots its causes across the fish’s body. The parasite causes fatigue, lethargy, and appetite loss. It also affects breathing.

If you spot Marine Ich, you must isolate your Blenny and begin treatment with an over-the-counter anti-parasitic. It’s also important to check your water conditions and restore proper parameters.

Food & Diet

Since the Lawnmower Blenny is herbivore, its diet consists of filamentous green microalgae, diatoms, and filamentous blue-green microalgae. These substances grow on rocks and tank walls, creating a thin film visible to the human eye.

While not primary food sources, these fish will also consume invertebrates, fish eggs, sponges, tiny snails, and organic material that settles at the bottom of the tank or that they happen by while searching for algae.

The main challenge of raising these Blennies is ensuring they feed. You must continually observe them to ensure they are rasping surfaces and have a fully-developed body with a rounded belly. It is common for Blennies to starve because they fully deplete available algae or reject prepared foods. Beyond monitoring to ensure the fish is eating algae, you should supplement their diet with prepared foods.

Author Note: Look for blends intended for herbivores to meet your Lawnmower Blenny’s nutritional needs. Excellent options for your Blenny to eat are algae pellets or cut-up pieces of nori. Frozen foods containing microalgae are good because they resemble the fish’s natural diet.

Base their feeding schedule on your observations, but offering meals a few times a week is usually adequate, especially if your Blenny consumes algae growing in the tank. Provide a large enough serving that takes the fish a few minutes to eat.

Starving Blenny

It’s critical to act fast if you believe your Lawnmower Blenny is starving. The best intervention is to provide multiple types of prepared foods and observe which ones the fish accepts. Blennies are notoriously picky eaters. Frozen plant foods, algae-based wafers, dried seaweed, and foods like brine shrimp or mysis are all options. Some aquarists even chop up cucumber, lettuce, and zucchini to coax their Blenny into eating.

While Blennies willingly consume organic materials that settle at the bottom of the tank, it’s critical for your tank’s health to remove decaying matter. Too much debris likely means you are overfeeding other tank inhabitants. The decaying organic material will release potentially harmful chemicals as it breaks down.

Behavior & Temperament

These Blennies have a lot of personality, making them ideal tank additions. They are highly observant fish and will often respond when you approach the tank. The Lawnmower Blenny is naturally curious and relatively active, spending much of their day zipping from rock to rock in search of food.

Other times, they are content to hide or remain stationary. Lawnmowers’ large eyes constantly move, creating the impression they are keeping tabs on the community’s comings and goings. Depending on the tank’s algae growth, you’ll be able to spot your Lawnmower Blenny’s teeth marks in the residue on the walls of your aquarium. These fish are not capable of harming the glass.

Author Note: While a generally easy-going fish, Lawnmowers may show aggression toward other algae-eating fish they see as competitors for food. While animals commonly compete for sustenance, algae is a slow-growing food source, upping the stakes for these herbivorous species.

In addition, agitated or distressed Blennies may nip at other fish and coral. Fortunately, the bites are not violent enough to cause significant damage because the Lawnmower’s teeth are adapted to consuming plants and algae. Proper tank size is essential to keep Lawnmowers calm and relaxed.

They will hide in the rocks when they feel threatened and at night when they sleep. It’s common to observe them with their faces sticking out from a crevice or gap, scanning the aquarium floor with their distinct large orbital eyes.

These Blennies also use their broad mouths to stir up the tank floor in search of small particles. They are not disruptive enough to upturn rock or disturb your tank. Beyond another fun behavior to observe, Blennies help the tank’s overall health because the decaying matter they turn up can filter out.

It’s usually best to keep a single Lawnmower. While non-aggressive with most other fish, they will attack other Lawnmowers if they feel threatened over food availability. Attempting to house multiple Blennies requires a tank with enough space and algae to keep each fish content.

Interestingly, despite spending most of their time at the bottom of the tank, Lawnmowers are excellent leapers. Tanks require secure lids to prevent them from jumping out.

Lawnmower Blenny Tank Mates

The Lawnmower Blenny lives peacefully with other community fish, except other Blennies. Suitable tank mates include:

  • Blue Reef Chromis (or the Blue Green Chromis)
  • Royal Gramma Basslet
  • Yellow Tang
  • Orchid Dottyback
  • Clams and other Sessile Invertebrates
  • Shrimp (like the Harlequin Shrimp)
  • Starfish
  • Crabs
  • Snails
  • Most Peaceful Community Fish (the Mandarin Goby could be one of them)

Avoid large, aggressive, predatory fish, including Sea Horses, Triggers, and Lionfish. Your Lawnmower will be intimidated and hide to avoid bullying and possible attacks. It’s best to forego docile bottom-dwellers like Gobies and Dragonets too. Your Blenny may attack and chase them off.

Interestingly, Lawnmowers are such voracious eaters that they may try to consume the algae from the scales of large, slow-moving creatures like Pipefish.


Aquarists and retailers do not have firmly established protocols for breeding Blennies. Specimens available for purchase are almost always wild-caught. The species’ aggression toward each other and ease of catching them in the wild make it unjustifiable to cultivate them in tanks.

Breeding a Lawnmower Blenny is possible but challenging. You must ensure you have a member of each sex and that your tank is large enough to accommodate two fish. Males and females have almost identical appearances, but males have slightly more prominent anal fins with extended spikes and more flesh.

Wild Blennies spawn between April and June when water temperatures rise. Increasing your tank water to 78°F and upping your feedings can encourage the fish to mate. Unfortunately, these fish are selective about partners. Simply housing a pair together does not guarantee they will mate.

If they breed, the female will lay fertilized eggs, covered in a sticky film, that attach to a surface or the substrate. The male will then guard the eggs until they hatch. Blennies do not eat their eggs or fry, but the young Lawnmowers will be vulnerable to tank mates. 

Author Note: Experts recommend using a separate breeding tank for your Lawnmowers to breed, but this is a sizable investment considering the low odds of successful mating.

Wrapping Up

The Lawnmower Blenny is a delightful and charming fish that is sure to bring joy to any saltwater aquarium. They are easy to care for, making them a great choice for beginner hobbyists. However, it’s important to keep in mind that these fish do require some specific care to thrive.

By providing your Lawnmower Blenny with a suitable tank setup, a varied diet, and some friendly tank mates, you can ensure that they live a happy and healthy life. It’s also important to keep an eye on their behavior and health, and to seek veterinary care if necessary.

Thank you for taking the time to read this care guide. We hope that it has been helpful and informative. If you have any further questions or concerns, don’t hesitate to reach out to us and best of luck with your new finned friend!


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