Pajama Cardinalfish Care Guide: Tank Size, Diet, Groups & Tankmates

The Pajama Cardinalfish (Sphaeramia nematoptera) is a small, calm fish with a yellow face, big red eyes, and orange polka dots. It is one of the easiest and most peaceful fish you can add to a reef tank.

Quick facts

• Tank size: 30 gallons or more
• Adult size: about 3 inches
• Diet: carnivore; mysis, brine shrimp, and small meaty foods
• Reef safe: yes, safe with corals and most invertebrates
• Difficulty: easy
• Temperament: peaceful and a bit shy

What makes it special

You may see it sold as the Polka-dot Cardinalfish, Spotted Cardinalfish, or Coral Cardinalfish. It comes from the calm reefs and lagoons of the Western Pacific, from Indonesia to Fiji.

Its body looks like it is wearing pajamas: a yellow-green head, a dark band across the middle, and a spotted back half. Those big eyes help it see in low light.

It is a slow, gentle swimmer. It spends most of the day hovering in one spot and gets more active in the evening.

Is it right for your tank?

This is a great pick for beginners who want a colorful fish that stays out of trouble.

• Good fit: peaceful reef tanks with gentle tankmates and some cover
• Poor fit: tanks with big, pushy, or fast-eating fish
• Nice bonus: it rarely bothers corals, shrimp, or snails

Tank setup

• Space: 30+ gallons for one or two; more room for a group
• Cover: branching corals, rock arches, or overhangs to hover near
• Flow: low to moderate; it is not a strong swimmer
• Lighting: any reef lighting is fine if it has shady spots
• Water: 75–80°F, salinity near 1.025, stable and clean

Add them once your tank has finished cycling and has been stable for a few weeks. Place rockwork so they have a calm, shaded area away from strong pumps.

Photo: Brian Gratwicke, Wikimedia Commons, CC BY 2.0

Feeding

Pajama Cardinals eat tiny floating animals in the wild. At home, they take most frozen foods.

• Frozen mysis shrimp and brine shrimp
• Finely chopped seafood or frozen reef blends
• Small pellets once they are eating well

Feed small amounts once or twice a day. Make sure food drifts near them, since faster fish may grab it first.

Keeping a group

These fish feel safer in a small group of three or more. A group also looks great hovering together.

• Add them all at the same time if you can
• Give a group more space, about 50 gallons or more
• Watch for one fish being chased, and remove it if needed

Males carry eggs in their mouths until they hatch. Spawning is common in captivity, but raising the babies is hard.

Health tips

Pajama Cardinals are hardy, but new fish can still bring in parasites.

• Quarantine: follow our 30-day fish quarantine protocol
• Look for: clear eyes, a full belly, and steady hovering
• Ask: to see it eat before you buy

Reef safety

It is fully reef safe. It will not nip corals, and it leaves clams, shrimp, and snails alone. Very tiny shrimp may be eaten, but this is rare.

Tankmates

• Good: clownfish, gobies, small wrasses, firefish, and other cardinals
• Risky: dottybacks and busy eaters that hog food
• Avoid: lionfish, groupers, triggers, and any fish big enough to eat it

Want a similar fish? Read our Banggai Cardinalfish care guide or browse the best nano reef fish.

FAQs

Is the Pajama Cardinalfish reef safe?

Yes. It ignores corals and is safe with most shrimp, crabs, and snails.

Can I keep just one?

Yes, one does fine on its own. A small group just looks better and feels more secure.

Why does it hide during the day?

It is most active at dusk. Give it a few weeks and some cover, and it will hover out in the open more.

Ready to add one?

Looking for Pajama Cardinals or peaceful tankmates? Browse fish from trusted sellers on the ReefBay shop.