The Lawnmower Blenny, Salarias fasciatus, is a peaceful community saltwater fish with a great personality and truly earns the name lawnmower, by mowing down microalgae in your tank.
Table of contents: Lawnmower blenny care
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Lawnmower blenny quick facts
- Common names: Lawnmower blenny, Algae blenny, Sailfin blenny
- Scientific names: Salarias fasciatus
- Size: ~4-5 inches (~10-13 cm)
- Minimum tank size: Mature ~55 gallons (200+ liters)
- Reef safe: Yes
- Care or experience level: Easy, if you have plenty of algae to eat; Moderate if you don’t, due to picky eating
- Preferred diet: Filamentous algae, diatoms, tiny crustaceans, detritus
- Original part of the world: Indo-Pacific reefs
As you can see in the pictures, the Algae blenny is typically tan/green/gray with small black or blue spots on the head, and darker stripes across its body. Particularly arresting and beautiful features of this fish, when you look at them closely, are their perched eyes, ringed with small dots, blunt head, big lips, and cirri on the top of their heads.
The Lawnmower Blenny (Sailfin Blenny) can live up to 2-4 years, but some specimens have even lived longer in well cared for aquariums.
Ideal habitat for the Sailfin blenny
Because of their special, even helpful dietary needs, the Lawnmower Blenny does best in a larger established tank with a moderate amount of natural algae to feed on, with their constant rasping/kissing of the rocks and glass. Provide a lot of caves and hiding places for the fish to feel secure and thus reduce stress. The Rock Blenny will usually dwell near the tank bottom, scraping algae off one rock at a time, and hiding in caves when things become stirred.
If your tank doesn’t have a lot of natural algae (which is probably a good thing, all things considered), be prepared to supplement the diet of your Lawnmower Blenny with prepared algae foods like spirulina flake or other foods for herbivores.
Lawnmower blenny tank size
The official recommendation is that the minimum tank size for a Lawnmower blenny is 55-gallons, although it is a bit complicated and that is not a universally accepted response. The Algae blenny is not an active, open-water swimmer. They, therefore, do not require a lot of open space to swim about. However, because of their relatively specialized diet and picky eating habits, they may require a bit more surface area to graze. They can also be a bit more aggressive in smaller tanks.
Based on the combination of factors there, it is likely best to only add them to a tank that is 55-gallons or larger.
The Lawnmower Blenny is likely to thrive only in established tanks with sufficient algae growth. It is an herbivorous fish and will happily eat microalgae or film algae as well as the occasional hair algae, although there are mixed reports about this—since some individuals seem to greedily eat it, while others tend to ignore it completely. Its combed teeth are used to continuously scrape algae off any surface in the tank.
As mentioned earlier, it is a best practice to supplement its diet with high-quality herbivore food.
One unfortunate problem with the Lawnmower Blenny is that they may starve, if your tank doesn’t have enough algae present, so it is important to keep an eye on the body shape of your Algae blenny, to look for signs of starvation/emaciation. A healthy blenny will have a smooth look and a rounded abdomen. If the abdomen looks pinched in, this is a clear sign that you have to feed them extra food. Depending on your tank, you may need to feed extra processed food several times a week, or at least once a day. You can determine the right food amount by watching your fish’s attitude and behavior and body shape.
Behavior and tank mates for the Sailfin blenny
A healthy Lawnmower Blenny has a curious and outgoing personality and will always be very aware of its surroundings. You may even notice that they seem to recognize you and ‘greet’ you when you get close to the tank.
Typical reef species are usually safe with this fish, but an occasional nip at shrimps or corals may occur. Lawnmower Bennies may be a bit too aggressive for lagoon species like pipefish or sea horses, so be ready to remove the Blenny if they begin to harass these other gentle creatures.
Don’t mix the Lawnmower Blenny with other similarly sized and shaped fish that would occupy the same niche or you may see aggression and fighting.
The Sailfin or Lawnmower Blenny is generally tolerant and peaceful when paired with other community fish, but as is typical with saltwater fish you will find that more than keeping more than one blenny per tank may cause some serious squabbles and injury unless those two fish become a compatible mated pair.
Even though algae is the preferred food of the Lawnmower Blenny, there are reports that this fish is prone to nip at clams and SPS coral polyps, so you should monitor this fish and use caution if you can’t tolerate a little nipper.
Selecting a breeding pair is very difficult, as males and females look quite the same, but males are sometimes a bit larger. This adds to the difficulty of breeding in captivity. One small difference may appear at the anal fin spines, which may be smaller on females and longer, capped with fleshy tissues in males.
If you are interested in breeding these fish, I recommend you check out this paper:
As well as the forums over on MOFIB
Let’s recap the pros and cons of keeping the Lawnmower Blenny
- Will clean up microalgae growing in the tank, on rocks, tank walls, or decorations;
- Hardy as long as nutritional requirements are met
- Generally, reef safe
- Inexpensive and readily available in many pet stores or aquarium supply shops
- May nip at clams or corals occasionally
- Occasionally territorial with other blennies
- Prone to starvation if nutritional needs aren’t met
Check out this Youtube video to learn more about the Lawnmower blenny.
If you are having challenges controlling aquarium algae, check out this article:
If you are looking for a few great fish to keep with the Algae blenny, consider:
You might be interested in some of these other algae-eaters
The Lawnmower Blenny is a popular and inexpensive algae-eating blenny with a great personality. At first glance, they may not seem super-attractive, but when you look close up, they really do have intricate, exquisite detail–and they make up for a lot, with a winning personality. What is your experience in keeping them?
Michael, Scott W. Marine Fishes: 500+ Essential-to-Know Aquarium Species. TFH Publications. Neptune City, NJ: 2001.
Michael, Scott W. “Fishy Grazers on the Reef and in the Aquarium”. Coral: the Reef & Marine Aquarium Magazine. Volume 12: Issue 4 Jul/Aug 2015