Lawnmower Blenny: Facts, Lifespan, Care, Feeding, & Breeding

The lawnmower blenny scientific name (Salarias fasciatus) is a greenish-brownish-colored algae eater with a smattering of blue spots that blend it perfectly with its surroundings. The blue stripes and spots on its body may change in brightness depending on its environment, becoming more muted at times, with a chameleon-like effect. The blenny’s appeal as the tank comedian is due in part to the shape of its head and eyes. Its head is blunt, and its eyes protrude, giving it a comical expression. It is a slender fish with one long dorsal fin.

Lawnmower Blenny


The lawnmower blenny goes by a variety of names, including algae blenny, sailfin blenny, jeweled blenny, and jeweled rock skipper. It is considered an asset to any saltwater tank, thanks to its insatiable appetite for algae.

Lawnmower Blenny Lifespan & Size

A blenny will usually mature between 4 and 6 inches in length. It tends to live for two to four years, or maybe longer. It needs a 30-gallon tank, at the minimum, to provide the best opportunity for plenty of algae. If the tank is larger, it will grow to its maximum length.

Behavior & Characteristics

Lawnmower blenny mouth closeup


The blenny is described as “funny.” Its mannerisms are likened to a salamander, in the way it darts about the tank, with its slender body and button-like, googly eyes. It seems to recognize its keeper, even coming out of hiding when its owner approaches the tank. Its habits are amusing, as it dashes from place to place and will hammer open-mouthed at its algae-covered rock, according to some experts, “like an aquatic woodpecker.” If it feels threatened, it will dart into a crack or cave and then stick its head out to see what’s going on.

The blenny has a row of fine teeth that it uses to gnaw and work on algae-covered surfaces, whether it is the aquarium wall or a decorative accessory. It will eat constantly and sometimes ingests other bits of matter, like snail shells and fish food that have dropped to the tank bottom.


The trickiest part about keeping a blenny is making sure it gets enough to eat. You can tell this visually by looking at the abdomen, which should be a healthy rounded shape. A blenny with a pinched midriff isn’t finding enough food.

Lawnmower blenny around rocks covered in algae


Although a blenny needs plenty of algae to survive, a common misconception is that it can survive on algae alone. The active and curious blennies make their home in East Africa, Indo-Pacific, and the Red Sea to Micronesia. Since blennies frequent shallow tropical waters, they find their sanctuary within the coral reefs. They circle areas with coral branches and sponges, scraping their way along the diverse sea bottom. Their feeding techniques are to pound and gnaw the coral, and as a result, they ingest detritus, or waste material primarily, from the coral. This includes bits of coral skeleton, sand, gravel, and other organic matter, such as fish eggs and tiny crustaceans.

Since a blenny in the wild does not subsist on solely algae, it stands to reason that their captive diet must be supplemented. If a blenny is not getting enough calcium carbonate in its diet, its condition will rapidly deteriorate. Therefore, it is important to offer an occasional selection of commercial algae-based wafers or pellets.

Some tank owners who like to promote a more natural lifestyle in their aquarium will opt for cultured algae rocks, rotating them into the tank every so often.

Lawnmower Blenny Care

A lawnmower blenny thrives in a large tank; the larger, the better. The blenny should be provided with a 30-gallon tank or larger. The size of the tank is related more to potential grazing, rather than swimming room. A high volume of algae in a small tank is not a good thing. Therefore, sufficient space for algae growth is desirable. If possible, there should be sufficient algae growing in the environment to keep it feeding on a steady basis. A blenny will appreciate a lot of rocks and caves to serve as hiding places. This will keep its stress levels at the lowest possible level and encourage its longevity. The blenny will spend most of its time on the tank bottom, scouring gravel and rocks. Because it is a tropical fish, a blenny will do best in temperatures that range from 75 to 84 degrees F (24 to 29 degrees C). Be sure to keep a deep layer of sand or gravel in the bottom of the aquarium, because blennies love to dig.

Tank Mates

Although the lawnmower blenny is notoriously passive with other fish that share its space, it can be aggressive to smaller ones. Like most other saltwater fish, it is selective about what tank mates it allows within its realm. It may not be safe to include tiny cohabitants, such as seahorses, in its tank or any fish that resembles another blenny.

Tank mates that are typically safe to live with blennies are:

There are certain types of fish that must be introduced with caution when planning to coexist with blennies. These include:

  • Other blennies
  • Cardinals
  • Dragonets
  • Grunts
  • Jawfish
  • Hogfish
  • Parrotfish
  • Triggerfish


If its tank is large enough to allow sufficient algae growth and it receives the correct supplements, a blenny should remain active and in good health. As with any other tropical saltwater fish, its tank water temperature must be maintained. To keep stress to a minimum, compatible tank mates should be maintained, taking care to avoid introducing any species that may provoke a fight.

The aquarium should be cleaned on a regular basis to discourage bacterial infections. Diseases such as ich, or white spot disease, can affect your blenny as well as others in your tank community. Also, like most other fish, blennies are vulnerable to fungal infections and parasites. Be aware that adding new fish to the habitat will risk infecting your current population. Be sure to quarantine new fish before introducing them to your tank environment.


Blennies are very difficult fish to breed due to their intolerance toward others of their kind. The only way to solve this is to raise two young blennies together. Another problem in breeding blennies is that it can be challenging to tell the two genders apart. Males may be a bit larger and have longer anal spines. The female will lay eggs that cling to the strata, whether there is a male present in the tank or not. The breeding season runs from April to June.

If cared for properly, your lawnmower blenny can offer you plenty of entertainment with its cartoonish appearance, friendliness, and animated behavior. Keepers of blennies even attest that the fish seems to recognize them and responds to their presence. The blenny can add a welcome balance to the tank environment. The blenny certainly has much to offer, and its tank-cleaning feature is a bonus to a fun aquarium experience.