A mottled, big-eyed bottom-dwelling blenny that perches on rocks and grazes film and hair algae all day, earning its name and its reputation as a living algae mower. Hardy and characterful, but it needs an established tank with enough algae or supplemental greens to stay fed.
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Indo-Pacific: from the Red Sea and East Africa across to the western Pacific
Origin
Old World
Climate
🌴 Tropical
Water type
🌊 Marine
Family
Blenniidae
Genus
Salarias
Part of the Blennies
Blennies are small, bottom-dwelling marine fish with scaleless bodies, blunt heads, and big expressive eyes, often perching on rocks or peering out from holes. The aquarium trade favors them for their comic personalities, useful algae-grazing habits in many species, and suitability for nano and reef tanks.
From the minimum an animal needs to be kept humanely, up to the ideal setup. Bigger is almost always better — minimums are floors, not targets.
Photo coming soon
Minimum
Algae-grazing reef
30 gal / 110 L mature reef
Lawnmower (Salarias fasciatus) blennies are herbivorous algae grazers — they need a tank already producing film/turf algae or they starve. Provide live rock with caves and a tight lid.
Photo coming soon
Recommended
Established reef with rockwork
55–75 gal / 200–280 L
More rockwork means more grazing surface and more perch ledges. Supplement diet with nori once natural algae is reduced. Keep only one blenny unless the tank is very large.
Photo coming soon
Ideal
Mature reef with sump refugium
75 gal+ / 280 L+ with refugium
Refugium produces a constant macroalgae food supply. Open swimming room plus a rocky maze gives the blenny territory boundaries and reduces nipping at coral polyps.
Life & growth stages
How this animal changes through its life — each stage often has its own care, diet and space needs.
Photo coming soon
Egg
Fish eggs are small, translucent spheres, often laid in clutches on plants, substrate, or in a nest — or carried/brooded by a parent in livebearing and mouth-brooding species. A dark eye spot and the curled embryo become visible inside as development progresses.
Photo coming soon
Fry
Newly hatched fry are tiny and semi-transparent, frequently still carrying a yolk sac that fuels them before they feed freely. They lack full fin structure and adult coloration, staying near cover until they can swim and forage on their own.
Photo coming soon
Juvenile
Juveniles look like miniature adults but with developing fins and muted or different markings; many species shift pattern and color as they mature. Growth is rapid at this stage given clean water and steady feeding.
Adult
Adults show the species' full size, finnage, and mature coloration, and are sexually mature. Many fish develop sex-specific differences in size, color, or fin shape, which can intensify during breeding.
Habitat & enclosure
Provide at least a 30-gallon tank with abundant live rock, which gives this dedicated grazer both the algae film it eats and the ledges and caves it perches in. Lots of rock surface area is more important than open swimming space, since the fish spends its day hopping from perch to perch and rasping algae. A secure lid helps, as blennies can leap, though this species jumps less than many.
Maintain stable reef conditions: temperature 72-79 F (22-26 C), pH 8.1-8.4, salinity 1.023-1.026 specific gravity, with low to moderate flow. Good lighting that encourages a film of algae actually benefits the fish, so a mature, slightly algae-rich tank is ideal.
Substrate
Substrate is secondary for this rock-grazer; fine sand over plentiful live rock is typical. The live rock itself is the key feature, providing grazing surface, perches, and hiding caves.
Equipment & setup
Standard reef gear suits it: a heater, moderate flow, and lighting strong enough to sustain a healthy film of algae for grazing. A protein skimmer keeps water quality high. A lid is recommended to prevent the occasional jump.
Diet
Primarily herbivorous, grazing constantly on filamentous and film algae and associated detritus on rock and glass. A single blenny can strip a small tank of hair algae quickly, after which it must be supplemented with dried seaweed (nori) on a clip, algae-based pellets and flakes, and blanched vegetables such as spinach or zucchini.
Many also nibble some meaty foods like mysis. The most common cause of decline is keeping one in a clean, algae-poor tank without enough supplemental greens, so plan to feed it like an herbivore once the natural algae runs low.
Behavior & temperament
Peaceful toward most tankmates and reef-safe with corals and invertebrates, though it can be territorial toward other blennies, gobies, or similar bottom-dwellers, especially in smaller tanks. Keep only one per tank unless the system is large. Occasionally a lawnmower blenny will nip at clams or LPS coral polyps if hungry, but this is uncommon when it is well fed.
It is an entertaining, expressive fish that props itself on its pectoral fins, swivels its periscope-like eyes, and 'mows' across surfaces. Expect lots of perching, hopping, and grazing rather than open-water swimming.
Health
Generally hardy, but the biggest welfare problem is slow starvation in tanks that lack enough algae; a sunken belly is the warning sign, so check for a rounded abdomen before buying. They can contract marine ich and velvet and should be quarantined and drip-acclimated. They scaleless skin makes them sensitive to copper medications and poor water quality.
Maintain stable parameters and ensure a steady algae or supplemental greens supply. Avoid adding one to a brand-new tank with no algae yet, and never rely on natural grazing alone long-term.
Tips, DIY & hacks
Add a lawnmower blenny to a tank already battling hair or film algae, but be ready to feed nori and algae foods once it has cleaned up, so it does not starve. Use a veggie clip or rubber-band a sheet of dried seaweed to a rock to keep it grazing. It is one of the most effective and entertaining natural algae-control fish for a peaceful reef.
