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Lawnmower Blenny Care Sheet

Blennies are undeniably cute and rather comical in both appearance and personality. The way they scoot around the tank is unique in the fish world and they tend to be very hardy aquarium residents. The Lawnmower Blenny is one of the most popular blennies in the trade and well worth adding to any fish-only or reef tank where green algae is starting to grow out of control!

lawnmower blenny

Getting to Know the Lawnmower Blenny

Lawnmower Blennies are staples of the marine aquarium hobby for good reason. They are excellent algae eaters and peaceful community tank residents. And on top of all this, they are interesting to watch in their own right. This species is found all over the IndoPacific region, from East Africa, throughout the Indian and Western Pacific, all the way to the Great Barrier Reef in Australia.

They have a broad, fleshy mouth that looks like a frog’s. The bulbous eyes, mottled pattern, and the way they tend to hop from one coral or rock perch to another adds to the effect. But instead of flies, Lawnmower Blennies spend their time biting at patches of algae and biofilm that accumulate on the hard surfaces of your tank. In fact, you’ll start setting their bite marks showing up on the glass if you have growths of either algae or biofilm there.

Lawnmower Blennies display a classic example of cryptic coloration. Better known as camouflage, cryptic colors help animals blend into their environment, even in plain sight. In a tank with mature live rock and coral you’ll often find yourself staring right at your Lawnmower Blenny without seeing it.

These fish can darken or lighten their shades of grey and brown as well as the patterns on their flanks to a surprising degree. While a Lawnmower Blenny will never win a beauty contest it’s a surprisingly attractive fish in its own right.

When settled in and happy the brown can darken into a deep purple and the white on their spots and belly will turn a rich cream. Their constantly darting eyes will even take on a knowing, iridescent green sheen as they watch you watch them. You may also notice small skin tags on their heads that look like weedy growths. These help them further blend into patches of algae when moving along rocks.

In short, Lawnmower Blennies are fun to watch, easy to care for, and inexpensive. Let’s talk about how to care for these intriguing grazers!

  • Common Names: Lawnmower Blenny, Algae Blenny, Sailfin Blenny, Jeweled Blenny
  • Scientific Name: Salarias fasciatus
  • Origin: IndoPacific
  • Length: 4-5 inches
  • Aquarium Size: 30 gallons
  • Temperament: Peaceful
  • Ease of Care: Very Easy

Lawnmower Blenny Care

Lawnmower Blennies are on the larger side for a blenny. But are hardy and easy to care for so long as you provide them with enough greenery!

Aquarium Size

With a maximum length of 4 to 5 inches we don’t want to keep a Lawnmower Blenny in a tank that’s too small. When young you can keep one as a nano reef inhabitant but as an adult, 30 gallons is the minimum for one. They are active fish but mostly crawl about, plucking at hard surfaces, so they don’t need as much water volume as you’d expect for a fish their size. Just make sure that your filtration is adequate for the fish you have.

One advantage of a larger tank is that it will grow more algae and biofilm, providing your Lawnmower Blenny with much more food. If you’re keeping other grazers, like Angelfish and Tangs, you’ll want to provide a spacious aquarium so all of these fish have a chance to consume their favored food source without too much competition.

Water Conditions

Lawnmower Blennies thrive in the conditions provided by most fish-only and reef tanks. Temperatures of 72-78℉ are ideal for them and the specific gravity (salinity) should fall between 1.020-1.025. And like most marine tanks, the pH should stay between 8.1-8.4, which is not hard to do when using a crushed aragonite substrate.

These fish are also hardy enough to withstand slightly elevated levels of ammonia, nitrite, and nitrates. This makes the Lawnmower Blenny a good first fish for newly cycling aquariums. Just be careful when feeding at first. You’ll have to feed since there isn’t going to be much algae at first in a new tank.

But there also isn’t much nitrifying bacteria, which process the ammonia and other nitrogenous wastes that accumulate. New tank syndrome is just as deadly for Lawnmower Blennies as it is for other fish.

Lawnmower Blennies do enjoy moderate to high levels of current, which helps oxygenate the water. This makes them a good match for reef tanks with current-loving corals as well like Green Star Polyps and Acropora.

Are Lawnmower Blennies Reef Safe?

Lawnmower Blennies are considered reef safe but you should keep an eye on your corals when the algae starts to run low. This is due to their grazing habits. They prefer eating exclusively vegetarian, plucking away at algae growths that form on live rock. But occasionally they may pick at the mantle of a Giant Clam or even the occasional LPS coral or SPS coral.

This is almost always because the Lawnmower Blenny has run out of algae to feed on and the aquarist isn’t providing it with enough regular food. Lawnmower Blennies are continual grazers so your feeding schedule may not be enough for it.

So long as you can supply it with regular greenery you should have no trouble with a Lawnmower Blenny in a reef tank. In fact, they are extremely beneficial and help algae from getting out of control and overwhelming your corals. Reef keepers find them to be an excellent addition to any saltwater cleanup crew!

Feeding Lawnmower Blennies

As you’d expect with a name like “Lawnmower Blenny,” these comical looking fish are almost entirely herbivorous. They feed on most types of green and macroalgae (but not coralline algae), providing a beneficial cleaning service for your live rock and corals. Keeping them well fed can be a challenge because they eat continually and grow up to 5 inches long. A single Lawnmower Blenny may pick your rocks clean over time.

Marine greenery is therefore the best food source you can offer them. Dried and processed seaweed is easy to come by and can be clipped in place, allowing the Lawnmower Blenny to feed. Just make sure that it gets a fair share since Tangs and other vegetarians will gladly monopolize the feeding clip.

If you’re running a refugium then you can also grow a fresh supply of chaetomorpha and other macro algae. Pieces plucked and clipped in place make great supplements to the blenny’s diet!

Lawnmower Blennies are flexible and will also snap up mysis shrimp, brine shrimp, pellets, and flakes fed to other fish. They are as much detritivores and opportunists as they are vegetarians, so variety is very important for them. Just make sure that a large portion of their diet is vegetarian for proper health!

Tank Mates for Lawnmower Blennies

Lawnmower Blennies are generally very peaceful and will ignore just about every other fish in their quest for greens and detritus. The only fish that tend to give them trouble are other bottom dwellers and other vegetarians.

Angelfish and Tangs can occasionally act aggressively towards other algae eaters. Algae is a slow growing resource and both of these types of fish have learned to drive away competition to maximize their grazing space. They will usually concentrate their efforts on other Angelfish/Tangs but may also pick at a Lawnmower Blenny.

Many Damselfish also eat (and even farm) algae and may act aggressively towards competitors. Though, to be fair, some Damselfish (especially the Dascyllus sp.) tend to be aggressive regardless of what the other fish eats.

Keeping them with other bottom dwellers can also be challenging. Blennies are often territorial towards other blennies. And given how large the Lawnmower Blenny gets, it will win any contests of strength. They may also chase off Gobies and Dragonets. But the less similar they are in appearance, the better your chances are of success. Having a spacious tank with plenty of grazing space also helps your Lawnmower Blenny feel more secure.

In the majority of cases your Lawnmower Blenny will be a peaceful community resident that keeps to itself and performs a valuable service. They are harmless to shrimp, corals (when well fed), anemones, and other fish.

Good Tank Mates for Lawnmower Blennies:

  • Most Peaceful Community Fish
  • Angelfish and Tangs (with caution)
  • Corals, Clams, and other Sessile Invertebrates (with caution)
  • Shrimp, Starfish, Crabs, and Snails

Poor Tank Mates for Lawnmower Blennies:

  • Other Blennies, Gobies, and Dragonets (can be kept together with caution)
  • Aggressive or Predatory Fish

Breeding Lawnmower Blennies

Unfortunately not much is known about the breeding habits of Lawnmower Blennies. They are exclusively wild caught and the two sexes look nearly identical. Couple that with their often territorial nature towards one another and you’ll find it next to impossible to ever breed them.

Fully grown adult males do have slightly elognated anal fin rays when compared to those of females. But other than that the two sexes look very similar to human eyes.

Blennies can be either demersal (substrate) spawners or pelagic (open water) spawners. Pelagic spawning is very common among reef fish, where the pair rises up into the water column, quickly releases their eggs and sperm, and then dashes back to the coral below.

Regardless of which method Lawnmower Blennies choose, be sure to take notes and let me know as you’ll likely be one of the first to breed these fish in captivity!

Jason Roberts
About Jason Roberts
Jason is an aquarium fanatic that has been a fish hobbyist for almost three decades.

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