Saltwater Fish

Pajama Cardinalfish

Sphaeramia nematoptera

Peaceful nocturnal cardinalfish that lives in groups · Beginner

Lifespan: 4-5 years
Adult size: 8 cm (3 in)
Min. habitat: Aquarium 110L+ / 30gal+
Social needs: Shoaling; keep in a small group
Diet: Carnivore (mysis, brine, frozen, pellets)
Time: Daily feeding; weekly testing/changes
Cost: Medium

Overview

The Pajama Cardinalfish has a silver-yellow face, a dark band across the body, and a polka-dotted rear, giving it a mismatched "pyjama" look.
It is peaceful, hardy, and reef-safe, and unlike most cardinals it does well living in a group, hovering together in the open during the day.

Naturally nocturnal, it becomes most active at dusk but adapts to feed during the day in aquariums.
Its slow, gentle drifting makes it a distinctive addition that contrasts with more active swimmers.

Housing

A cycled 110L (30 gal) or larger tank lets you keep a small group among live rock and branching coral cover.
Maintain salinity 1.024-1.026, temperature 24-27°C (75-80°F), pH 8.1-8.4, and nitrate low.
Moderate flow and a covered top are best.

Provide overhangs and branching structure where the group can rest and feel secure.
Stable, clean water and ample cover keep these gentle fish confident and out in view during daylight hours.

Diet

The Pajama Cardinalfish is a carnivore.
Offer frozen mysis and brine shrimp, finely chopped seafood, and small marine pellets, fed once or twice daily.
Being naturally nocturnal, some appreciate a feeding near dusk.

They can be timid eaters, so make sure boisterous tankmates do not take all the food first.
Target-feeding shy individuals helps them keep weight.
A varied meaty diet maintains their condition and gentle, hovering activity.

Health

Pajama Cardinalfish are hardy and disease-resistant in stable water.
The main risks are stress from aggressive tankmates, underfeeding when outcompeted, and marine ich following poor quarantine or unstable parameters.

Quarantine new fish, keep nitrate low, and watch for thin bellies or hiding, which suggest a fish is not eating enough.
A peaceful tank with good cover and reliable feeding keeps these fish in good health.

Temperament

Peaceful, slow-moving, and reef-safe, the Pajama Cardinalfish is harmless to corals and most invertebrates, though very small shrimp may be eaten.
It does best kept in a small group rather than alone.

Lone fish tend to be reclusive, while a group of three or more drifts confidently in the open.
Pair them only with calm tankmates, as fin-nippers and aggressive fish will keep them hidden and stressed.

A good fit for

Beginners wanting a peaceful group
Reef community tanks
Keepers who like calm, hovering groups
Dusk-active display tanks

Common mistakes to avoid

Keeping just one (becomes reclusive)
Fast tankmates stealing their food
Pairing with aggressive or fin-nipping fish
Insufficient hiding cover causing stress

Is your enclosure big enough?

Minimum volume110 litres (29 US gallons)

CompanyCannot be kept alone. The minimum is 3, and the space above is for that group.

Check your own enclosure against this

Is this urgent?

In a reef, stability matters more than any single target number. A parameter moving fast does more damage than a parameter sitting slightly off.

Go now

Any detectable ammonia or nitriteWater change now with matched, mixed and aerated saltwater. Stop feeding. Directly toxic, and a marine system has less margin than a freshwater one.

Now

Temperature or salinity has moved sharplyCorrect slowly, over hours, not minutes. Check the heater and the top-off. The speed of the change does the damage. Correcting fast repeats the injury in the other direction.

Now

Rapid gilling, or a fish hanging in the flow breathing hardIncrease aeration and check temperature and salinity. Warm water holds less oxygen, and a heater failure shows up here first.

Now

Today

White spots, or a fine dusting like icing sugarIdentify which parasite before treating. Most reef tanks cannot be treated in place. The two common parasites look similar and need different handling; velvet can kill a tank in days.

Today

Corals closed for more than a day, or receding tissueTest alkalinity first, and compare it against the last reading rather than a target. Unstable alkalinity is the most commonly cited coral killer, and a swing shows up in the trend, never in a single point.

Today

A new fish added without quarantine now looks unwellRemove it to a separate system today if you can. Nearly every wipeout in a reef tank traces back to a skipped quarantine.

Today

Quarantine every new animal, including corals and inverts. It is the single practice that separates a reef that lasts from a reef that restarts.

This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it — and the time to find one is before you need one.

What it really costs

Setup, monthly, first year and across a whole life, itemised and with the electricity worked out from the actual wattage. Published figures for the same animal disagree by a factor of four, so the calculator shows ranges rather than picking one.

Work out the cost of a pajama cardinalfish

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