Jewelled blenny
Salarias fasciatus
Also known as: Lawnmower blenny, Sailfin algae blenny, Algae blenny, Sailfin blenny, Jeweled blenny, Jeweled rockskipper
This is the classic "lawnmower" blenny - a little reef perch-fish that spends its day scooting around the rocks, scraping film algae and looking like it has tiny eyebrows. Give it a mature tank with lots of live rock to graze and it will stay busy all day, but if the tank is too clean it can slowly starve unless you supplement greens.
The Jewelled blenny exhibits vibrant green and blue scales, alongside a distinctive elongated dorsal fin and bold, elongated body shape.
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Quick Facts
Size
14 cm
Temperament
Semi-aggressive
Difficulty
Intermediate
Min Tank Size
30 gallons
Lifespan
2-6 years
Origin
Indo-Pacific
Diet
Herbivore-leaning grazer - natural microalgae/film algae, plus dried seaweed (nori), spirulina/algae-based foods; will often take some meaty frozen foods
Care Notes
- Give it lots of real rock with algae and holes to perch in - they spend most of the day hopping, grazing, and wedging into crevices.
- Keep salinity steady around 1.024-1.026 and temp 76-79F; they hate swingy tanks more than slightly-off numbers.
- Feed like a grazer: nori on a clip, spirulina/algae pellets, and frozen herb blends; if you only do meaty foods they can get skinny and picky.
- New tanks with "clean" rocks starve these guys fast - if your glass and rocks never get a green film, plan on daily algae-based feeding.
- They are usually fine with peaceful reef fish, but they can get spicy with other blennies and similar perchers (especially in smaller tanks).
- Watch for them bullying timid gobies out of favorite caves, and also for them getting bullied by dottybacks or aggressive wrasses.
- Cover your tank - they can jump when startled, and the blenny-on-the-floor thing happens way too easily.
- If you ever see a hollow belly or stringy poop, bump up veggie foods and check for internal parasites; they are hardy, but they crash when they stop grazing.
Compatibility
Good Tankmates
- Peaceful clownfish (Ocellaris or Percula) - they mostly mind their own business in the water column while the Jewelled blenny does its rock-perching and algae grazing
- Chill gobies like Watchman gobies or Neon gobies - different hangout zones, and gobies are usually too relaxed to get into turf wars with a blenny
- Reef-safe wrasses that are not bullies (Fairy or Flasher wrasses) - active swimmers that do not usually park on the blenny's favorite rocks
- Smaller, laid-back damsels like Chromis (not the feisty domino types) - they can handle a bit of blenny attitude without turning the tank into a boxing match
- Most peaceful reef fish like Banggai cardinals - slow but not usually fin-targets, and they do not compete for the same algae patch
- Blennies and goby-like fish that are not algae blenny lookalikes, like a small firefish if your tank is calm and covered (the blenny might posture, but usually leaves them alone if not crowded)
Avoid
- Other algae blennies and close cousins (Lawnmower blenny, Starry blenny, other Salarias) - in real tanks they often scrap over the same rock and food, especially in smaller setups
- Aggressive damsels and dottybacks (Domino/Three-stripe damsels, Pseudochromis) - they tend to pick fights and the blenny will not back down
- Territorial big boys like some hawkfish or triggers - they can harass a blenny that likes to sit out in the open, and the blenny can get stressed or beat up
- Very shy, easily bullied fish in cramped tanks (small firefish in a rowdy tank, timid assessors) - the blenny can get pushy about its favorite cave and keep them pinned in a corner
Where they come from
Jewelled blennies (Salarias fasciatus) come from shallow reefs and rocky lagoons across the Indo-Pacific. You will usually find them perched on rock, scooting from spot to spot, and rasping algae all day like a tiny lawnmower with attitude.
That wild lifestyle explains basically everything about keeping them: give them rock, give them algae and films to pick at, and give them a few little caves to claim.
Setting up their tank
These guys are happiest in a mature reef or rock-heavy fish-only tank where the rocks have some real life on them. A brand-new sterile setup is where a lot of people struggle, because the blenny runs out of grazing fast and starts looking skinny.
- Tank size: I would not do one in less than 30 gallons, and 40+ makes the feeding/grazing balance way easier.
- Rockwork: lots of surface area and ledges. They love to sit in the open but want a bolt-hole 2 inches away.
- Flow: moderate is fine. They are perchers, not open-water swimmers.
- Cover: use a lid or mesh top. They can hop, especially during spats or at night.
- Lighting: any reef lighting is fine, but some light helps grow the films and algae they pick at.
If you are buying one for algae control, wait until the tank has some real algae and film growth. A jewelled blenny in a squeaky-clean new tank is a common setup for a slow starvation situation.
What to feed them
Even if yours pecks all day, do not assume the tank is feeding it. A lot of jewelled blennies look busy but still lose weight. I like to watch the belly line: they should look a bit rounded, not pinched in.
- Staples: dried nori sheets (clip them low near the rock), spirulina-based flakes/pellets, and herbivore blends.
- Frozen foods: mysis and brine can work as a supplement, but do not make it the whole diet.
- Natural grazing: encourage algae and microfilm on rocks (and even the back glass). They will work it all day.
Teach them the nori clip early. Once they recognize it as food, it saves you a lot of stress if the tank goes through a low-algae phase.
Feeding frequency depends on how much grazing the tank offers. In my tanks, I still give some kind of algae-based food most days. If you have lots of tangs or rabbitfish, plan on feeding extra because the blenny will get outcompeted at the clip.
How they behave and who they get along with
Personality-wise, they are bold, curious, and a little bossy for their size. Most of the time they are entertaining perch-and-peck fish, but they can get territorial about their favorite rock.
- Good tankmates: clownfish, gobies, cardinals, wrasses (most), smaller peaceful angels, and typical reef-safe community fish.
- Use caution with: other blennies (especially similar-looking algae blennies), some dottybacks, and very pushy damsels that claim the same rock zones.
- Watch for: nipping at similar-shaped fish that perch (some blennies pick fights with other bottom-perchers).
They are not a guaranteed 'clean-up crew' fish. Some individuals will nip at fleshy corals or clam mantles, especially if they are underfed. Most are fine, but keep an eye on it.
They generally ignore shrimp and snails. If yours is going after coral, the first thing I try is more algae-based food and a reliable nori routine. A hungry blenny makes bad choices.
Breeding tips
Breeding can happen in home tanks, but raising the babies is the hard part. The male will usually claim a tight cave or hole and guard the eggs. You might notice him getting extra defensive and doing little display moves near the entrance.
- Give them options: small caves, barnacle clusters, or tight rock crevices work well for spawning sites.
- Stable tank and lots of food: conditioning is mostly about steady grazing plus extra meals.
- If eggs show up: the male guards them. Try not to mess with the rockwork or do big disruptive maintenance near the nest.
The larvae are tiny and planktonic, so raising them usually means a separate larval setup and live foods (rotifers, then copepods/Artemia). Fun project, but not a casual weekend experiment.
Common problems to watch for
- Slow starvation: the big one. They look active but get thinner over weeks. Watch the belly and offer nori/spirulina foods regularly.
- Aggression in small tanks: chasing or constant posturing, especially with other blennies or similar perchers.
- Jumping: can happen after a scare or during territorial spats. A lid saves lives.
- Picking at corals/clams: usually tied to not enough vegetable matter in the diet or a tank that is too clean.
- New tank syndrome: tanks without mature rock/algae films often lead to weight loss unless you are on top of supplemental feeding.
If your jewelled blenny is hiding nonstop or breathing hard, do the boring checks first: salinity, temperature swings, ammonia, and oxygenation. They are tough once settled, but they do not love unstable new systems.
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