Pajama Cardinalfish
Sphaeramia nematoptera
Peaceful nocturnal cardinalfish that lives in groupsBeginner
- Lifespan
- 4-5 years
- Size
- 8 cm (3 in)
- Social needs
- Shoaling; keep in a small group
- Time
- Daily feeding; weekly testing/changes
- Cost
- Medium
- Diet
- Carnivore (mysis, brine, frozen, pellets)
Overview
What is this animal?
- 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.
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
Enclosure
Minimum 110 litres (29 US gallons) — for a group of 3
Cannot be kept alone. The minimum is 3, and the space above is for that group.
- 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.
Supplies
Setup
- Tank, stand and sump
- Return pump and powerheads
- Protein skimmer
- Reef lighting
- Rock and sand
- Salt mix, refractometer and test kits
- Quarantine tank
Ongoing
- Frozen mysis shrimp
- Frozen enriched brine shrimp
- Frozen or live copepods
- Small marine pellets
- Vitamin or HUFA soaking supplement
- Turkey baster for target-feeding
- Small thawing cup and strainer
Safe substrate: Aragonite sand · Dry or cured live rock · Bare bottom
Care routine
Daily
- Check salinity, temperature and flow
- Head-count and look everyone over
- Several small feeds a day
- Top up evaporation with fresh water
Weekly
- Service the skimmer and filter socksevery 3 days
- Clean the glass
- Test the water
Monthly
- Water changeevery 2 weeks
- Calibrate the refractometer
- Check salt, RO/DI and reagents
Less often
- Deep-clean pumps and powerheadsevery 3 months
- Replace RO/DI filter mediaevery 6 months
Vet: Quarterly condition review — every 3 months
Top resources for more info
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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.
Is your enclosure big enough?
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
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.
Bedding and substrate
In a marine system the rock and the sand are life support, and how you start them decides the first six months.
Safe
With a caveat
Never
This is our general list for saltwater fish. We have not built one specific to Cardinalfish yet.
My kit says 0.25 ppm. Is that dangerous?
A liquid kit measures total ammonia, but only the un-ionised fraction is really toxic, and that fraction is governed by pH and temperature — each whole pH unit multiplies it roughly tenfold. So the same reading can be nearly harmless in one tank and lethal in another; this works out which one you are in.
Compare with other animals
The same axes for every animal, side by side — the way the guides are written makes that a fair comparison rather than two articles.
Cardinalfish, side by side
Same axes, same care guides — the honest way to choose between types.
See all Cardinalfish side by side →
