The Lawnmower Blenny: a Funny, Fascinating Fish of Unpredictable Utility

Lawnmower Blenny (Salarias fasciatus)

Lawnmower Blenny (Salarias fasciatus)

The lawnmower blenny, aka the jeweled blenny, jeweled rockskipper, or sailfin blenny (Salarias fasciatus), is commonly purchased not just for its comical behavior and only-a-mother-could-love looks, but also for the utilitarian purpose of controlling algae in marine tanks. While you can pretty much count on this droll little fish to provide interest and entertainment, its performance when it comes to eradicating problem algae from aquaria can best be described as hit-or-miss.

Physical traits

S. fasciatus is “all blenny,” with an elongated body; long, continuous dorsal fin; blunt head; wide mouth; high-set, bulbous eyes; and frilly cirri on the head above and below the eyes. Color-wise, this fish is mottled in shades of brown, green, and white, and the eyes feature white stripes extending outward from the pupil in a radial pattern. Maximum length for this species is around 5 inches.


The lawnmower blenny’s natural diet consists primarily of detritus and microalgae, which it continually rasps off the rockwork and substrate. One of the potential challenges of keeping this species is that aquarium specimens don’t always learn to accept prepared foods, so it’s important to keep them in well-established tanks with a good supply of their natural food items. Specimens kept in newly set up or overly “sterile” systems often starve. Those that do come around to prepared foods can be offered various green foods, such as frozen herbivore formulations and algae-based pellets.

S. fasciatus has an elongated body, long, continuous dorsal fin, and blunt head common of blennies

S. fasciatus has an elongated body, long, continuous dorsal fin, and blunt head common of blennies

With one of its many common names including the word “lawnmower,” you’d envision this fish mowing down irksome algae with joyful abandon. But if you’re introducing S. fasciatus strictly for the purpose of eradicating, say, hair algae, it’s important to manage your expectations because individual results will vary. There’s also something of a paradox to keeping this species for the utilitarian purpose of algae control: In order to sustain the blenny, an ongoing crop of algae must be present in the system—but then eliminating algae was the reason for adding the fish to begin with.


Always watching...

Always watching…

Being a bottom-dwelling species that hops around the rockwork and substrate, S. fasciatus does not demand much in the way of open swimming space. It does, however, need enough rockwork and substrate to support the microalgae and detritus it feeds upon, so don’t sell it short with respect to tank size. I wouldn’t go much smaller than 40 gallons, with bigger being better.


Lawnmower blennies are moderately peaceful but likely to fight with conspecifics, congeners, and similar species. And the smaller the tank, the more likely your blenny will squabble with tankmates it perceives as competitors for food or real estate.

These blennies can generally be considered reef safe, but like many herbivorous fish, their natural grazing activity may include nipping at sessile invertebrates.


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. Wow! This really is one facinating fish! And from the looks of it, it can be a very useful addition to the aquarium.
    Thanks for sharing this info and letting us see up close and in detail this amazing little creature!

  2. Matt Bowers (Muttley000) says

    Another great write up Jeff!

  3. Paul Baldassano says

    These guys are actually very common and I often see them hanging around on one small rock in the shallow water of sandy Caribbean beaches where nothing else lives. Fascinating little fish.

  4. I always use Lawnmower Blenny for my 60-gallon tank. It looks so fascinating and very useful addition to my fish tank.

  5. It looks very cute. Do you have any for your tank?

  6. I got one for each of my tanks and they are a blast! Great personalities and started attacking the algae right away. If you have room a must get for their antics.

  7. Wow, what an excellent fish! This is unique one fish and I think it gives me a better look if I put in my aquarium. I have a 40 gallon and 60-gallon aquarium. I am confused. In which aquarium I can put the lawnmower blenny safely? Thanks for the share.

  8. Look fascinating. Great post Jeff

  9. Love these guys. They eat Algae like it’s candy. Though I don’t agree that it’s ugly – sure, it has a bit of a snout but I love their natural colours and patterns.

  10. This is a must have fish in my list as well. I have one in each tank. You need to get used to the dust in the water because of the constant sand sifting, but the job these fishes are doing worth it. And personally I don’t find them ugly at all. 🙂 They are pretty cool!

  11. this is my first time to see such fish . we will try to know more it . we are a professional aquarium supplies supplier . welcome to visit us if you need . website :

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