Livestock · Cardinals & Basslets
Pajama Cardinalfish
Sphaeramia nematoptera
A quirky polka-dot schooler that drifts calmly in the open — great in a group.
Difficulty: BeginnerReef-safe community fishReef-safe
The pajama cardinalfish (Sphaeramia nematoptera) is a quirky polka-dot, red-eyed drifter that hangs calmly in the open — and unlike its cousin the Banggai, it actually likes company. Keep a small group, feed in the evening (it's a night owl), and it's one of the easiest, most peaceful reef fish going.
Care at a glance
| Adult size | About 3 in (8 cm). |
|---|---|
| Lifespan | About 2–5 years. |
| Minimum tank | 20 gallons for a small group; 30+ is better for a proper shoal. |
| Temperature | 75–82°F (24–28°C). |
| pH | 8.1–8.4. |
| Specific gravity | 1.020–1.026 (≈35 ppt; keep it stable). |
| Other targets | Calm, low–moderate flow; keep nitrate low. |
| Diet | Not picky — flake, pellet, frozen mysis and brine shrimp, live blackworms. It's a nocturnal/crepuscular feeder, so an evening feed suits it best. |
| Temperament | Peaceful and slow-moving — and genuinely social: keep a group (odd numbers, at least 3, ideally 5+). Singles or pairs aren't recommended. |
| Reef-safe | Yes — definitely reef-safe; it leaves coral polyps and clam mantles alone. |
| Natural range | Western Pacific and parts of the Indian Ocean (Australia, Fiji, Japan). |
The fish store gets these wrong
Common myths, kindly corrected — no shame for having believed them.
- “All cardinalfish fight in groups.” Not the pajama — unlike the Banggai, pajama cardinals are peaceful schoolers that do best in a group.
- “It's not eating — it must be sick.” Often it's just nocturnal. Pajama cardinals are most active and hungry in the evening; try a dusk feed before worrying.
Before you buy
- Buy a small group (3+, ideally 5+), not a single.
- Plan an evening feed — they're night owls.
- Give calm water and some open mid-water to drift in.
- Captive-bred is available (e.g. ORA) — a good, hardy choice.
Quarantine and get help if…
We can't diagnose from a photo — but these are the signs to stop watching, quarantine, and get an aquatic vet or an experienced reefer's eyes on it:
- White salt-grain spots, flashing, or rapid gill-breathing (possible ich or velvet).
- Cloudy skin patches, clamped fins, or gasping at the surface.
- Refusing even an evening feed for days, or a hollow belly.
- Any new fish added without quarantine.
Never
- Never keep a single pajama cardinal expecting natural behaviour — they're social.
- Never assume it's sick for skipping daytime food — feed at dusk.
- Never add it to an uncycled tank.
Common pajama cardinalfish questions
Should I keep pajama cardinalfish in a group?
Yes. Unlike the Banggai cardinal, the pajama cardinal is a peaceful schooler — keep an odd-numbered group of at least 3 (5+ is better in a larger tank). Singles or pairs aren't recommended.
Are pajama cardinalfish reef-safe?
Definitely. They leave coral polyps and clam mantles alone and are one of the most peaceful reef fish you can add.
Why won't my pajama cardinal eat during the day?
It's probably just nocturnal. Pajama cardinals are most active and hungry in the evening — try a dusk feed before assuming a problem.
What size tank do pajama cardinalfish need?
About 20 gallons for a small group; 30+ gallons is better for a proper shoal with open water to drift in.
How long do pajama cardinalfish live?
About 2–5 years with good care.
Sources & further reading
This guide was written and fact-checked against these authorities. It's honest, general guidance — not a diagnosis, and not a substitute for an aquatic vet or your own test kit:
- Saltwater Aquarium Blog — Pajama Cardinalfish — size, lifespan, tank, water, diet, group recommendation, temperament, reef-safe, range
- LiveAquaria — Pajama Cardinalfish — care level, group recommendation, captive-bred availability
Written and fact-checked by The Coralkin Team against marine-aquarist and veterinary sources — if your pajama cardinalfish shows a red-flag sign above, quarantine and get an aquatic vet or an experienced reefer's eyes on it. We never guess a care number.
🔬 Review status: team-written and fact-checked against cited sources · not yet reviewed by a marine vet. How we research & fact-check →