Gilbert's cardinalfish

Where they come from

Gilbert's cardinalfish hang around sheltered reefs and lagoons in the Western Pacific. Picture loose clouds of tiny, glassy fish tucked under branching corals during the day, then gliding out at dusk to pick zooplankton from the water. They like shade, structure, and calm pockets out of the main current.

Setting up their tank

They stay small, but they look and act best in a group. A 30-40 gallon tank handles a group of 5-7 without feeling cramped. Give them a reefy layout with lots of overhangs and caves. They will choose a shaded roost and hover there most of the day.

• Temperature: 75-81 F (24-27 C)
• Salinity: 1.024-1.026
• pH: 8.0-8.4, stable alkalinity
• Zero ammonia and nitrite; nitrate under 20-30 ppm
• Flow: moderate with calmer eddies under and behind rockwork
• Lighting: reef lights are fine, but provide shaded areas
• Lid: tight-fitting lid or mesh top - they can jump during spooks or at lights-out

What to feed them

Small mouths, big appetites. They go for tiny planktonic foods and learn prepared foods if you keep portions bite-sized. Feed 2-3 small meals a day, with at least one offering near dusk when they perk up.

• Frozen: cyclops, calanus, rotifers, enriched baby brine, finely chopped mysis
• Dry: 0.5-1 mm pellets for nano fish, high-quality marine flakes crumbled fine
• Live (great for new arrivals): copepods or live brine shrimp enriched with algae or Selco

How they behave and who they get along with

Peaceful, social, and a little shy under bright light. In a group they hover in a loose cluster and do short dashes to grab food. They are not fast swimmers, so avoid tankmates that blast around or bully.

• Good tankmates: small gobies and blennies, firefish, peaceful fairy/flasher wrasses, assessors, pipefish in mellow setups, reef-safe shrimp and snails
• Use caution: assertive clowns, dottybacks, damsels, large hawkfish, boisterous wrasses that may outcompete them at feeding
• Reef-safe: they ignore corals and inverts

Breeding tips

They are paternal mouthbrooders. In a settled group, you may see a pair form and the male will hold a clutch of eggs in his mouth. He stops eating while holding, which can last 10-14 days.

• Watch for an enlarged, bulged jaw on the male and a refusal to eat - that is your cue he is holding.
• If you want to raise the fry, move the holding male to a quiet nursery tank with matching water and dim light. Gentle flow only.
• Fry are tiny and need rotifers and copepod nauplii at first. Keep the water clean, green-tinted (phytoplankton helps), and food density high.
• Many folks just let nature take its course in the display. Without dedicated rearing, nearly all fry get eaten.

Common problems to watch for

• Not eating: Often the food is too big or competition is too strong. Offer smaller planktonic foods and feed at dusk. Target-feed the shy ones.
• Getting outcompeted: Spread food in multiple spots and use a feeding ring under their favorite overhang.
• Stress under bright lights: Give more shade and darker backgrounds. They relax fast with cover.
• Skin and gill issues after import: Quarantine new fish. Cardinals can carry flukes and external parasites. Prazipro for flukes and observation before copper/other treatments as needed.
• Pinched bellies despite feeding: Consider internal parasites - a round of food-soaked metronidazole or levamisole (in QT) can help, guided by proper instructions.
• Jumping during spooks: Keep a lid, reduce sudden light changes, and avoid slamming cabinet doors near the tank.