Lawnmower Blenny – Species Profile & Facts

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The lawnmower blenny is the most popular cleaning fish for marine reef tanks, as its main activity is grazing for algae.

Blennies have earned their rightful spot in the aquarium trade thanks to their adaptability, behavior, and ability to fit in any community setup.

Sure, they can get grumpy at times and slightly territorial towards other fish, but they won’t go out of their way to harm or disturb their tankmates.

What is a Lawnmower Blenny?

Lawnmower blennies are marine reef fish that rank as bottom feeders. They spend most of their lives around reef structures and near rocks, constantly grazing for algae and other meal opportunities.

You can easily identify the blenny by its somewhat unusual looks. Blennies have long and slender bodies with dull colors in the grey-brown range.

Most are also spotted or display a variety of camouflaging patterns that allow them to blend within their environment.

The blenny’s body is designed to camouflage with the reefs and rocks they dwell on.

The fish also has bulbous eyes and fairly large mouths, making them resemble a toad.

The dorsal fin is long, covering the blenny’s entire back, and the abdomen is flat, which is typical for a bottom feeder.

Lawnmower Blenny Requirements

If you’ve never had a lawnmower blenny before, now’s the time to get up-to-date with its essential living parameters.

These include:

Tank Size & Setup

The lawnmower blenny requires a lot of swimming space, typically around 40 gallons or more. This is quite amazing, considering that blennies rarely go above 5 inches and can’t be described as adept swimmers.

They will spend pretty much all of their time lurking around rocks and reef structures, constantly grazing, resting, and scanning their environment.

The ideal setup should include a lot of rocks and reef structures with caves and various hiding areas. Just keep in mind that blennies rank as high-risk fish when it comes to reef safety.

They are known to pick on polyps and are capable of causing a lot of damage in the process.

Always monitor your blennies’ behavior to make sure they don’t get carried away by their polyp-nipping behavior.

Algae are beneficial because they keep the blenny occupied and well-nourished. Live plants are optional but welcomed as they keep the environment healthy and well-oxygenated.

Make sure there’s enough swimming space available. Not for the blenny, but rather for its tankmates so that they can keep their distance from the lawnmower.

Blennies are known to be quite territorial, especially towards members of the same species.

If you plan on housing more than 1 blenny in the same tank, make sure that the fish have sufficient room to prevent tensions.

Water Requirements

The core water requirements for the lawnmower blenny include:

  • Temperature – 72-78 °F
  • pH – 8.1-8.4
  • Salinity – 1.020-1.025
  • Lighting – Medium

Some moderate water movement is also beneficial, as it keeps blennies happier and more comfortable.

Important note regarding lighting: blennies hate bright lights. Keep their habitat moderately lit so that they feel safer and hidden. These fish like to keep a low profile.

Live plants also help in this sense to shelter them and create a more natural-looking setup.

Feeding and Diet

Lawnmower blennies are on a constant lookout for food. They are herbivorous fish that prioritize algae and detritus above anything else.

While they can do just fine with algae alone, you should feed them some extra veggies occasionally for a plus of nutrients.

That’s because blennies have quite a varied diet in the wild compared to captivity. They roam and scrape the substrate for whatever they can find, including algae, detritus, plant matter, and even fish eggs and larvae. You should add some greens to their diet for a more well-rounded culinary experience, but there’s a catch.

Lawnmower blennies are rather pretentious about their food. So, they might not like any fish food or unfamiliar veggies and prefer to stick to their environmental algae.

To circumvent the problem, get your first blennies at a young age and teach them to appreciate new foods along the way.

Adult blennies are more likely to refuse unfamiliar food as adults than young.

Do Lawnmower Blenny Need a Heater?

Yes, they do. The blenny’s water temperature variates slightly in the wild, but it remains overall stable within the safe parameters.

The blenny’s aquarium should replicate these conditions to keep the fish healthy, comfortable, and calm in its environment.

A heater is great in this sense because it stabilizes the water temperature and prevents wild fluctuations that could cause your blenny to experience stress or shock.

These are more likely to occur based on your geographical positioning and the tank’s placement. So, yea, I recommend investing in a heater just to be safe.

Do Lawnmower Blennies Need a Filter?

Yes, blennies need a filter. As a cleaning fish, it may not sound like lawnmower blennies are in need of a filter, but you would be mistaken.

The filtration system plays a defining role in the ecosystem’s stability, keeping the water clean, moving, and well-oxygenated. It’s also great for plants.

Just make sure to adjust the filter’s power and intake properly. Reef structures are incompatible with fast water currents, and neither are blennies.

Also, place the filter’s intake such that you don’t risk it sucking in substrate, plants, or rocks from the surrounding area. You can use the same reasoning regarding the output.

Don’t place it too close to the fish’s dwelling area, plants, or reef structures, and keep the water flow manageable based on what benefits the environment.

How Much do Lawnmower Blennies Cost?

Lawnmower blennies vary in price between $20 and $50, depending on the fish’s size and pattern.

Although, few people appreciate blennies for their coloring and color pattern characteristics. These fish are overall bland, and they have to be to blend in with their environment.

In essence, blennies are more expensive than your regular freshwater fish like guppies, mollies, platies, swordtails, etc.

But they’re definitely worth it when it comes to creating a clean and stable marine community tank.

What is the Lifespan of Lawnmower Blennies?

Lawnmower blennies live up to 4 years in optimal conditions. Provide the fish with stable water parameters, good food, and a stress-free environment, and they will thrive.

The tank’s layout will have the most impact on your blenny’s health state.

This fish is rather timid and territorial, so it likes to spend its days lurking around the substrate and self-designated territory near the reef. You will see it resting on rocks or grazing for algae residues around its nest.

The fish demands its personal space to be respected. Otherwise, it can grow aggressive and experience stress if other fish engage in frequent incursions into its territory.

So, finding some compatible tankmates for your blenny is key in preserving the fish’s healthy state of mind.

How Big do Lawnmower Blennies Get?

Lawnmower blennies grow up to 4-6 inches. Their growth rate and overall size depend on their diet, genetic profile, environmental parameters, and overall health.

Stressed blennies won’t grow as large and will experience stress-related diseases due to a weaker immune system.

The same goes for fish kept in sub-par conditions with dirty waters or frequent water parameter fluctuations.

This reinforces the need for a heater, a good filtration unit, and a water tester kit so you can monitor their aquatic setup regularly.

Are Lawnmower Blennies Aggressive?

Yes, they are. Blennies won’t go out of their way to attack other fish but won’t accept any intruders either.

By ‘intruders,’ we mean fish with a habit of bothering blennies or roaming their territory too often.

Besides that, blennies don’t care too much about fish swimming in the same tank. They do care, though, about other blennies. These are not social creatures, so you should limit the number of blennies you have per tank.

Especially males. Male blennies are extremely aggressive towards one another, so you shouldn’t keep more than one per tank.

Lawnmower Blenny Tankmates

Lawnmower blennies are generally peaceful and docile with other fish species, provided:

  • Their tankmates are not too aggressive, territorial, or inquisitive
  • Are not too large, which may cause them to see blennies as food, or too small for blennies to see them as food
  • Prefer different swimming areas to prevent territorial disputes (so, try to avoid active bottom-dwellers)
  • Are not too similar in appearance, which could trigger the blenny’s “I need to fight this invading blenny right now” behavior

Other than that, blennies should be easy to accommodate in a community setup. As a plus, consider adding more plants and water decorations for a more varied setup and hiding-and-exploration areas.

This should keep all fish busy and too occupied to trespass each other’s boundaries.

Are Lawnmower Blennies Good for Beginners?

I wouldn’t recommend lawnmower blennies to beginners, despite what you may read elsewhere.

First, caring for the fish’s habitat is a challenge in and of itself. Marine fish are more difficult to accommodate, especially cleaners like the blenny, which needs a varied and rich environment.

Then you have the fish itself, which requires specialized care itself. While blennies are generally self-sustainable, capable of living off of whatever their environment provides them with, things are not as easy.

Here’s what I mean:

  • They require a more varied diet than what their habitat provides, but they’re extremely pretentious about their food
  • They don’t like the company of its own species, so it’s difficult keeping more than one blenny
  • They are generally peaceful but will become aggressive and nip at other fish at times.
  • You need to aquascape the environment based on their preferences since they need so much space

In other words, the blenny is the protagonist of the story. If you plan on setting up a marine tank and adding a blenny into the mix, keep in mind that the entire ecosystem should revolve around accommodating the blenny first and the rest of the fish last.

How to Tell if Lawnmower Blenny is Male or Female?

There are few-to-no differences between blenny males and females. Female blennies tend to be smaller than males, but this isn’t always true.

So, you might end up with 2 blenny males, at which point hell is bound to ensue. Many aquarists prefer to keep blennies solo to circumvent this problem altogether.

How do Lawnmower Blennies Breed?

If you want to know how blennies breed, that makes 2 of us. Realistically, there are no reports on blennies breeding successfully in captivity.

The primary reason is the difficulty of sexing the fish, so many people end up with either 2 males or 2 females.

Then the second problem is the compatibility between the 2. Even if you get a male and a female in the same habitat, there’s no guarantee that the 2 will even mate.

Blennies are as pretentious about their partners as they are about their food.

It’s also unclear what environmental requirements the fish need during the mating season, although we can theorize based on the fish’s behavior in the wild.

Blennies spawn during summer when temperatures rise, so the same principle should apply in captivity.

However, since we can’t determine the parameters necessary to breed the species, I advise against even attempting it. It’s bound to create more problems than solutions.


Lawnmower blennies are generally peaceful fish that demand personalized care. While they’re not fit for complete novices, they’re not that difficult to maintain either.

So long as water parameters are stable and they have sufficient food to eat, blennies will thrive.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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