Fellow Creatures
Saltwater Fish

Lawnmower Blenny

Salarias fasciatus

Comical algae grazer with plenty of personality  ·  Beginner

Lawnmower Blenny

Dirk Godlinski · CC BY-SA 3.0 — Wikimedia Commons

Lifespan
4-6 years
Adult size
10-13cm (4-5in)
Min. habitat
Aquarium 110L+ / 30gal+
Social needs
One per tank unless the system is large
Diet
Herbivore, marine algae
Time
Low
Cost
Medium

Overview

  • The Lawnmower Blenny is a hardy, characterful herbivore named for its habit of grazing algae off rock and glass.
  • With perching pectoral fins, expressive eyes, and constant activity, it is a popular beginner reef fish.
  • It is reef-safe and useful for nuisance algae, but it needs an established tank with a real algae supply.
  • Keepers must be ready to supplement food once the algae is grazed down.

Housing

  • House in a mature reef of at least 110L (30 gallons) with plenty of live rock covered in algae film and perches to rest on.
  • An established tank with diatom and green algae growth provides natural grazing.
  • Keep temperature 24-27C (75-81F), salinity 1.024-1.026, pH 8.1-8.4, and ammonia and nitrite at zero.
  • A tank that is too clean or too new will leave this grazer underfed.

Diet

  • Primarily a herbivore, it grazes hair algae, diatoms, and film algae from rock and glass.
  • Once natural algae is depleted, supplement with dried nori, seaweed sheets, spirulina flakes, and algae-based pellets.
  • Many lawnmower blennies slowly starve in tanks without enough algae, so a sunken belly signals the need to feed more vegetable matter.
  • Some will eventually accept meaty frozen foods as well.

Health

  • Hardy and relatively disease-resistant compared with many marine fish, but it still benefits from quarantine and stable water.
  • The most common cause of death is starvation in tanks with insufficient algae rather than illness.
  • Watch the belly profile: a pinched, concave stomach means it is not getting enough food.
  • Provide constant grazing material and supplemental nori to keep weight and energy up.

Temperament

  • Peaceful toward most tankmates but territorial toward other blennies and similar bottom-dwelling fish.
  • Keep only one lawnmower blenny per tank unless the system is large, to avoid squabbling.
  • It is an amusing, interactive fish that perches openly, hops between rocks, and shifts colour with mood.
  • It generally ignores corals and invertebrates, making it a reliable, peaceful reef community member.

A good fit for

  • Beginners wanting a hardy, fun fish
  • Reef tanks with nuisance algae
  • Keepers who will supplement with nori
  • Community reefs needing a peaceful grazer

Common mistakes to avoid

  • Starves in tanks lacking enough algae
  • Watch for a pinched, concave belly
  • Keeping two blennies together causes fights
  • Adding to a brand-new, algae-free tank
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