Pajama Cardinalfish

1) Where they come from

Pajama cardinals (Sphaeramia nematoptera) come from the Indo-Pacific—think calm lagoons and reef edges where they hang around branching corals and spiky urchins for cover. They’re not open-water speedsters; they’re “hover and watch” fish. That explains about 90% of their behavior in a tank.

2) Setting up their tank

If you give these fish a peaceful tank with lots of places to duck into, they settle in fast. They don’t need crazy flow or a huge runway to swim laps—what they want is structure and shade.

• Tank size: 20–30 gallons works for a pair or small group, bigger is always easier for groups
• Rockwork: caves/overhangs plus some “branches” (rock fingers, faux coral, or macro) so they feel secure
• Lighting: they’re fine under reef lights, but they appreciate darker pockets and not being blasted in the open
• Flow: moderate; avoid turning the whole tank into a washing machine
• Cover: yes—cardinals can and do jump when spooked

3) What to feed them

They’re easy eaters once they recognize food, but brand-new ones can be shy at first. Pajama cardinals are built for picking meaty bits from the water column—small chunks, not flakes blowing around the surface.

• Go-to foods: mysis shrimp, brine shrimp (better enriched), chopped krill, small marine pellets, frozen blends
• Feeding rhythm: small amounts once or twice a day beats a single big dump
• If they’re timid: start with frozen mysis/brine and feed after lights dim a bit—often they get bold fast

4) How they behave and who they get along with

These are mellow, slightly goofy fish. They hover, they stare, and they don’t start fights. That said, they do have a “personal space bubble,” especially as they mature.

• Temperament: peaceful, mostly ignores other species
• Best tankmates: other calm community reef fish (gobies, blennies, firefish), cleaner shrimp, most inverts
• Works in reefs: yes—reef-safe and won’t bother corals
• Potential issues: aggressive dottybacks, hawkfish that think small fish are snacks, big wrasses, large predatory fish

5) Breeding tips (actually doable!)

Breeding pajama cardinals is one of the cooler things you can see in a home tank because the male mouthbroods the eggs. If you keep a healthy pair and feed them well, they may just decide to do it without you “trying.”

• What you’ll notice: a pair hanging close, then the male holds a clump of eggs in his mouth
• During brooding: the male often eats little or not at all—don’t panic right away
• If you want babies: move the male to a quiet rearing tank near the end, or collect fry once released
• First foods for fry: rotifers and/or baby brine shrimp (newly hatched), then graduate to larger foods

6) Common problems to watch for

Pajama cardinals are pretty hardy for a saltwater fish, but the usual reef problems still apply—stress, parasites, and getting bullied at feeding time.

• Not eating the first few days: usually shyness; offer frozen mysis/brine and feed smaller portions more often
• White spots/flashing: marine ich/velvet can hit cardinals like anything else—quarantine new fish if you can
• Sudden hiding and heavy breathing: check ammonia/oxygenation, and make sure flow isn’t blasting their resting spot
• Fin nips: typically from semi-aggressive tankmates; cardinals rarely “fight back”
• Jumping: happens after a scare—lids and covered overflows save lives