Lawnmower Blenny

Overview

General Description: A robust, expressive combtooth blenny famous for scraping algal film from rock. It is useful in mature aquariums but should be chosen as a pet with specialized feeding needs, not purchased as a guaranteed cure for nuisance algae.

Appearance: A mottled olive, tan, gray, and brown body with irregular dark bars, pale blue or white spots, a blunt head, mobile eyes, and branched cirri above the eyes that resemble eyebrows.

Personality: Bold, watchful, and comical once settled. It frequently perches in full view, surveys the aquarium, and hops between grazing sites.

Notable Characteristics: Uses comb-like teeth to scrape biofilm, detritus, and algae from hard surfaces. Lacking a functional swim bladder, it rests on the bottom or perches rather than hovering continuously.

General Suitability: Best for an established medium or large reef or fish-only aquarium with extensive mature rock, natural film growth, plant-based supplemental foods, and no competing territorial blenny.

Natural Habitat

Native Distribution: Indo-Pacific from the Red Sea and East Africa to Samoa and Micronesia, north to southern Japan and south to Australia

Ocean/Region: Tropical Indian and western-central Pacific Oceans

Depth: Intertidal shallows to approximately 8 m (26 ft), most often only a few meters deep

Reef Zone/Habitat: Algae-rich reef flats, shallow lagoons, seaward reefs, estuarine rubble patches, and mixed coral-sand-rubble areas

Natural Water Movement: Low to strong depending on the reef flat; aquarium conditions should include good oxygenation and varied flow

Natural Behavior: Usually solitary, perching in weedy or rubble areas and repeatedly scraping biofilm and algae from rocks and coral outcrops.

Other Habitat Notes: Its mottled pattern changes subtly with surroundings and helps camouflage it against algae-covered rubble.

Aquarium Setup

Minimum Tank Size: 40 gallons; 55 gallons or larger is preferable for long-term grazing area and stability

Preferred Tank Dimensions: A wide, mature aquarium with extensive horizontal rock surface is more valuable than extra height

Rockwork: Provide large amounts of stable, mature porous rock with exposed grazing surfaces, caves, ledges, and crevices

Hiding Places: Include several caves and sheltered recesses large enough for the adult fish

Open Swimming Space: Maintain some open bottom and short swimming lanes, but prioritize broad grazing surfaces and secure perches

Substrate: Sand or fine aragonite with rock and rubble areas is appropriate

Water Flow: Moderate and well oxygenated with both active flow and calmer resting sites

Lighting: Lighting that supports controlled film and microalgal growth is beneficial

Lid Requirement: Strongly recommended because blennies can jump when startled or chased

Special Setup Requirements: Use a mature aquarium with established biofilm. Guard overflows and pump openings, secure rockwork, and do not add the fish to a sterile new system solely to address a temporary algae bloom.

Water Parameters

Temperature: 75-82°F (24-28°C)

Specific Gravity/Salinity: 1.023-1.026 (approximately 32-35 ppt)

pH: 8.1-8.4

Alkalinity: 7-11 dKH, kept stable

Other Relevant Parameters: Ammonia 0 ppm; nitrite 0 ppm; keep nitrate and phosphate controlled without stripping the aquarium of all natural film growth

Water Quality Sensitivity: Generally hardy, but sensitive to ammonia, oxygen depletion, abrupt salinity changes, and long-term nutritional deficiency

Stability Requirements: Maintain consistent temperature, salinity, pH, alkalinity, and oxygenation; replace evaporated water regularly and avoid abrupt corrections.

Behavior & Social Needs

General Behavior: Perches on rock, substrate, coral bases, and equipment, then makes short hopping swims between grazing patches and shelter

Aggression: Usually peaceful toward unrelated species, but it can be assertive toward similar blennies and competing bottom-dwelling grazers

Territorial Behavior: Low to moderate toward dissimilar community fish; moderate to high toward conspecifics and similarly shaped algae blennies

Activity Level: Moderate and primarily diurnal

Swimming Level: Lower to middle levels around rockwork

Group Requirements: No group is required. Keep one per aquarium unless a verified compatible pair is available and ample territory is provided.

Pairing: A compatible male-female pair may coexist, but two randomly selected individuals can fight over grazing areas and shelter

Other Notable Behaviors: Color can lighten or darken with mood and surroundings. Perching, hopping, and leaving visible grazing marks in soft film algae are normal.

Reef Compatibility

Reef Safe: Generally yes

Coral Compatibility: Usually leaves healthy corals alone, although occasional nipping at fleshy coral tissue may occur when food is inadequate

Invertebrate Compatibility: Safe with shrimp, snails, crabs, worms, and other common reef invertebrates

Potential Risks: May nip clam mantles or fleshy corals, knock loose small unsecured frags while moving, and attack similar grazing blennies

Conditions Affecting Compatibility: Risk rises when natural biofilm is depleted, plant-based supplementation is inadequate, or several territorial grazers compete for the same rockwork.

Tank Mates

Good Tank Mates: Ocellaris Clownfish, Royal Gramma, Common Firefish, Yellow Watchman Goby, Pajama or Banggai Cardinalfish, peaceful wrasses, and reef-safe invertebrates

Use Caution With: Other Salarias or combtooth blennies, tangs or rabbitfish in limited grazing space, territorial damsels, dottybacks, hawkfish, and large clownfish pairs

Avoid: Large predators, highly aggressive fish, persistent fin-nippers, and another territorial algae blenny in a small or medium aquarium

Same-Species Compatibility: Usually best kept singly. Adults can be strongly territorial unless they form a compatible male-female pair.

Same-Genus Compatibility: Avoid mixing with other Salarias species in most home aquariums because body shape, diet, territory, and shelter requirements overlap

Compatibility Notes: Provide ample mature rock and more than one feeding area. Watch for chasing, torn fins, prolonged hiding, a hollow belly, or exclusion from favored grazing surfaces.

Diet & Feeding

Natural Diet: Biofilm containing detritus, microalgae, filamentous algae, microbes, and tiny invertebrates scraped from reef surfaces

Captive Diet: A varied detritivore and herbivore-leaning omnivorous diet supported by natural grazing

Recommended Foods: Spirulina and marine algae pellets or flakes, softened nori or other marine algae sheets, quality herbivore gels, mysis shrimp, enriched brine shrimp, and frozen omnivore blends

Feeding Frequency: Offer one or two small supplemental meals daily while allowing continuous grazing

Feeding Behavior: Spends much of the day rasping rock and glass. Some individuals readily accept prepared foods; others require patient training with foods placed near a favorite perch.

Special Nutritional Requirements: Track abdominal fullness and provide marine plant matter even when algae is present. Natural growth alone may not sustain an adult, and not all nuisance algae are edible.

Sexing & Breeding

Male/Female Differences: Sexing is difficult. Mature males may show elongated front anal-fin rays and genital-papilla differences, but casual size and color comparisons are unreliable.

Breeding Difficulty: Advanced; spawning may occur, but rearing the small planktonic larvae requires specialized live foods

Reproductive Strategy: Oviparous substrate spawner with demersal adhesive eggs and a planktonic larval stage

Pair Formation: A compatible pair requires sufficient grazing territory and separate retreats. Incompatible adults may need immediate separation.

Spawning Behavior: The female deposits adhesive eggs within a protected nest or crevice. The male guards, cleans, and fans the clutch until hatching.

Eggs/Larvae: Eggs are demersal and attach to the substrate through filamentous adhesive pads. Newly hatched larvae enter the plankton.

Larval Care: Use a dedicated rearing tank with gentle aeration, stable water, rotifers or copepod nauplii as first foods, and carefully staged enrichment and transition to Artemia.

Captive Breeding Availability: Limited; most Lawnmower Blennies offered in the aquarium trade are wild collected.

Health

Common Health Concerns: Marine ich, velvet, flukes, intestinal parasites, bacterial infections, emaciation from insufficient biofilm or supplemental food, jumping injuries, and shipping stress

Parasite Susceptibility: Can contract common marine external and internal parasites; wild-caught specimens should be observed closely during quarantine

Disease Susceptibility: Physically hardy but nutritionally vulnerable. A fish that fails to accept prepared foods can slowly starve even while visibly grazing.

Signs of Stress: Rapid breathing, white spots or dusting, damaged fins, pale or very dark coloration, prolonged hiding, reduced grazing, refusal of prepared food, or a pinched abdomen

Quarantine Considerations: Use a covered quarantine tank with PVC shelters and algae-coated inert material when feasible. Offer several plant-based and small meaty foods and verify intake and feces.

Common Keeper Mistakes: Buying it only to fix algae, placing it in a sterile or undersized tank, assuming all visible algae are edible, failing to supplement its diet, keeping it with another territorial blenny, and overlooking weight loss

Special Sensitivities: Chronic underfeeding, copper overdosing, aggression from similar grazers, low oxygen, rapid parameter changes, and uncovered openings

Beginner Suitability

Beginner Friendly: With caution

Why: It is generally hardy, personable, and peaceful, but success depends on a mature aquarium and proof that the individual consumes supplemental foods

Major Challenges: Preventing slow starvation, providing sufficient grazing area, transitioning wild-caught fish to prepared diets, and avoiding territorial conflict with other blennies

Before You Buy

Important Considerations: Select an alert fish with a rounded belly, clear eyes, intact fins, normal breathing, and a demonstrated response to prepared algae-based food. Confirm that the aquarium is mature, covered, and large enough.

Adult Size: Up to about 5.5 inches (14 cm)

Aggression: Peaceful overall but territorial toward similar blennies and competing grazers

Reef Compatibility: Generally reef safe

Dietary Requirements: Detritivore and herbivore-leaning omnivore requiring mature biofilm, marine plant matter, and some small protein-rich foods

Long-Term Requirements: A stable, covered 40-gallon-or-larger mature aquarium, preferably 55 gallons or more, with extensive rock, varied feeding, and compatible tank mates for approximately 3-6 years

Species-Specific Information

Anything important that does not fit above: Despite its common name, the Lawnmower Blenny is not a predictable algae-removal tool. Its natural intake includes detritus-rich biofilm as well as algae, and aquarium specimens sometimes ignore long hair algae. The most important purchase check is a full abdomen and a demonstrated willingness to eat appropriate prepared food.