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Lawnmower Blenny Aquarium Care
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. As is typical for any saltwater fish, the lawnmower blenny is also known by several other names, including Algae Blenny, Sailfin Blenny, Rock Blenny or Jeweled Rockskipper Blenny. Of course, if you want to impress your scientist friends, practice your Latin or otherwise avoid any chance of misunderstanding you could always use the less frequently argued name Salarias fasciatus. But if you can’t already tell, I’m partial to the name Lawnmower Blenny.
The diminutive Lawnmower Blenny originates from tropical shallow waters, like the Great Barrier Reef, Indo-Pacific areas or even the Red Sea and Micronesia.
As you can see in the pictures, this fish is typically tan/green/gray with small black or blue spots on the head, and darker stripes across its body. A particularly arresting and beautiful feature of this fish are its perched eyes contrasting with the blunt head.
The Lawnmower Blenny (Sailfin Blenny) can live up to 2-4 years, but some specimens have even lived longer in well cared for aquariums. Maximum size is reported to be 4-6 inches, depending on the source.
Because if 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. 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.
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.
LiveAquaria recommends 30 gallons as a minimum tank size. This is not a large tank, by saltwater aquarium standards, but my opinion, on top of that advice, is that the size is important to provide adequate food for the fish, more so than swimming room and territory.
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.
The Lawnmower Blenny is likely to thrive only in established tanks with sufficient algae growth. It is an herbivorous fish and will happily eat micro algae 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 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
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 pipe fish 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.
Selecting a breeding pair is very difficult, as males and females look quite the same, but males are sometimes a bit larger. This adds tot 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
Pros and cons
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
The Lawnmower Blenny is a popular and inexpensive algae eater with a great personality. What is your experience in keeping them?