Jewelled blenny

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.

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.

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 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.

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.