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title: "Lawnmower Blenny: The Complete Reef Algae-Control Guide" description: "The definitive lawnmower blenny (Salarias fasciatus) care guide: the reef's natural algae mower, why it can starve in clean tanks, diet, reef-safe behaviour, and tank mates." slug: lawnmower-blenny commonName: Lawnmower Blenny scientificName: Salarias fasciatus family: Blenniidae order: Blenniiformes difficulty: Beginner minTankSize: 30 temperature: "75–82°F (24–28°C)" ph: "8.0–8.4" hardness: "Marine — SG 1.020–1.026" lifespan: "2–4 years" maxSize: "5 inches (13 cm)" origin: "Indo-Pacific" publishedAt: "2026-06-05"

Lawnmower Blenny: The Complete Reef Algae-Control Guide

The lawnmower blenny is the reef tank's natural algae control crew — a comical, big-eyed, perching blenny that "mows" film and hair algae off the rocks and glass, hopping from spot to spot with bags of personality. Salarias fasciatus is hardy, peaceful, reef-safe, and a genuinely useful natural algae-eater. The one catch is the flip side of its appetite: in a too-clean tank it runs out of algae and can starve, so you must be prepared to supplement its diet.

This guide is the complete reference: lawnmower blenny biology, its algae-control value, why it can starve, diet, reef-safe behaviour, and tank mates.

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Species Overview

The lawnmower blenny (Salarias fasciatus), also called the jewelled or sailfin blenny, is a marine blenny reaching about 13 cm (5 inches). It has a mottled brown-grey, camouflaged body, big expressive eyes set high on the head, and a comical face — it perches on rocks and the substrate, propped on its pelvic fins, and hops from spot to spot grazing. Its appearance and "perch-and-hop" behaviour give it loads of character.

The lawnmower blenny is hardy, peaceful, reef-safe, and a natural algae-eater — its name comes from how it "mows" film and hair algae off the rockwork and glass, earning its keep as biological algae control. It's rated beginner-friendly, with the key caveat being diet: it eats algae voraciously, so in a clean tank with little algae it can starve, requiring supplemental dried marine algae and weaning onto prepared foods. With good care it lives 2–4 years. For a reef with an algae problem (and a keeper ready to supplement), it's a useful, entertaining, hardy addition.

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Natural History and Origin

Salarias fasciatus ranges across the Indo-Pacific on algae-covered reef flats and rubble zones, where it spends its day grazing film and filamentous algae from rocks and surfaces, perching and hopping between feeding spots. It's a dedicated herbivore/detritivore adapted to rasping algae and detritus, with a camouflaged body and high-set eyes suited to a perched, surface-grazing life.

This algae-grazing lifestyle is the whole basis of its aquarium value and its main pitfall. It's an effective natural controller of nuisance film and hair algae, but it's specialised for a constant algae supply — in the wild it grazes all day over abundant reef algae, so in a captive tank with limited algae it can run short of food. This is why the lawnmower blenny "earns its keep" in an algae-rich tank but can starve in a clean, algae-poor one unless supplemented. Its grazing, perching, camouflaged, surface-feeding biology all shape its care: a mature, algae-having tank, and a plan to supplement food.

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Water Parameters

Lawnmower blennies need stable, mature marine conditions — crucially, a tank with established algae growth for them to graze. Mix salt with RO/DI water, target salinity with a refractometer, and add them only to a fully cycled, mature, algae-having tank — confirm with the nitrogen cycle tracker and the water parameters reference. Adding one to a brand-new or spotless tank risks starvation.

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Tank Setup Guide

Tank size

A lawnmower blenny needs a minimum of 30 gallons (115 litres), with more better — they need enough rockwork (and thus enough algae-grazing area) to feed themselves, and they're territorial enough to want space. A larger, algae-rich reef supports them best.

Aquascape — rock and algae

Provide plenty of live rock with algae-covered surfaces for grazing and perches/crevices to rest on and shelter in. The key is a mature tank with established algae — the blenny's food source. They're reef-safe and won't harm corals or invertebrates (they graze algae, not coral), though a hungry one may occasionally pick at coral or rasp surfaces.

Filtration, flow, lid

Run a standard reef system. A lid is sensible (blennies can jump). The priority is a mature, algae-rich reef with ample rockwork — without algae, the blenny will need heavy supplemental feeding.

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Feeding Guide — Don't Let It Starve

The lawnmower blenny's care comes down to diet: it eats algae voraciously, so a clean tank can't sustain it without supplementation.

What to feed

• Natural film and hair algae in the tank — its primary, preferred food (the reason to add one).
• Dried marine algae (nori) — clip a sheet for grazing; essential supplementation, especially as it grazes the tank clean.
• Spirulina/algae-based foods and herbivore preparations — important staples; try to wean it onto these.
• Some keepers offer mysis occasionally, but it's a herbivore — the diet must be algae-forward.

How often

Provide grazing algae plus supplemental nori/algae foods daily. The critical point: a lawnmower blenny in a clean tank will starve if not supplemented — watch its body condition (a sunken/pinched belly is a starvation warning), and provide dried algae and herbivore foods, weaning it onto prepared foods. A healthy lawnmower blenny is full-bodied, actively grazing and perching. Never assume a "clean-up crew" fish feeds itself indefinitely.

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Behaviour and Tank Mates

Lawnmower blennies are peaceful, comical, and full of character — they perch on rocks propped on their fins, hop between grazing spots, and watch the tank with big expressive eyes. They're reef-safe and peaceful toward most species. The main behavioural note is territoriality toward other blennies (and sometimes similar bottom-perching/grazing fish) — keep only one lawnmower blenny per tank, and be cautious mixing it with other herbivorous blennies or gobies that compete for the same algae and perches.

Toward unrelated fish they're peaceful. Good tank mates include percula clownfish, royal gramma, banggai cardinalfish, firefish goby, tangs, and other peaceful reef fish. Avoid other blennies (territorial) and very aggressive fish. Their personality and algae-mowing make them a favourite functional-yet-entertaining reef fish. Use the compatibility checker.

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Breeding Guide

Lawnmower blennies are rarely bred in home aquaria — they lay demersal eggs (attached to surfaces, often in a crevice, guarded by the male), but rearing the larvae is difficult, requiring small live foods and specialised larval care beyond most home setups. Spawning occasionally occurs in reef tanks, but successful rearing is uncommon.

For keepers, the lawnmower blenny is a functional and characterful display fish to enjoy for its algae control and personality. Choosing healthy specimens (with a full belly, not sunken) and ensuring an algae-rich tank or supplemental feeding is the practical focus.

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Health and Disease

Lawnmower blennies are hardy, with the leading risk being starvation rather than classic disease.

Starvation is the number-one issue — a lawnmower blenny in a clean, algae-poor tank that isn't supplemented slowly starves (sunken belly, lethargy); prevent it with an algae-rich tank and diligent dried-algae/herbivore-food supplementation. Marine ich (Cryptocaryon) and velvet can affect them — treat in quarantine (note scaleless-bodied blennies can be sensitive to medications, so research dosing). Bacterial infections follow poor water or injury.

Prevention: add them only to a mature, algae-rich tank, supplement food diligently (watch body condition), quarantine new fish, keep parameters stable, and keep only one blenny. Given algae and supplemental feeding, the lawnmower blenny is a hardy, entertaining, useful reef fish.

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Interesting Facts

• A natural algae mower. It grazes film and hair algae off the rocks and glass, earning its name as biological algae control.
• Perch and hop. It props itself on its pelvic fins, perching on rocks and hopping between grazing spots — full of comical character.
• It can starve. Its voracious algae appetite means a clean tank can't feed it — supplementation is essential, a common oversight.
• Big expressive eyes. Its high-set, mobile eyes and comical face give it standout personality.
• One per tank. Territorial toward other blennies, it's best kept singly.

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Bringing It Together

The lawnmower blenny is the reef's entertaining natural algae-control crew — a comical, big-eyed, perching blenny that mows film and hair algae off your rocks and glass while charming you with its personality. The keys to keeping it well are an algae-rich, mature tank (its food source) and a readiness to supplement its diet with dried marine algae and herbivore foods, because its voracious appetite means a clean tank will starve it (watch for a sunken belly). Keep one per tank (it's territorial toward other blennies), pair it with peaceful reef fish, and quarantine it. Add one only to a tank with established algae, supplement diligently, and it'll graze and perch its way through your reef for years as a useful, hardy, characterful addition. It complements algae-grazers like the yellow tang and foxface rabbitfish. Plan the build with the AI Tank Blueprint generator and the compatibility checker.