Glass Cardinalfish (Apogon Leptacanthus) saltwater aquarium fish portrait

The Glass Cardinalfish (Apogon leptacanthus) is a diminutive Indo-Pacific species that matures at roughly 2.5 inches, with a translucent body that reveals the skeletal structure beneath and gives the fish its common name. Its delicate build and understated coloration make it a subtle rather than showy addition, and the effect is strongest when several individuals hover together in open water above the reef structure.

Adult housing should begin at 50 gallons, which provides the open swimming space this schooling species uses along with the rockwork it retreats into when startled. Branching stony corals are a natural fit, as Glass Cardinalfish frequently shelter among Acropora branches in the wild and will do the same in a mixed reef display. Plan the layout so that clear midwater lanes sit adjacent to dense cover, and keep flow and lighting typical of a reef aquarium.

This is a group fish, and a shoal of five or more individuals is strongly preferred. All members should be added to the tank at the same time, since staggered introductions tend to leave later arrivals at a disadvantage. Care level is Moderate, largely because the species is shy, requires a settled group, and needs a calm environment where it can feed without competition.

Glass Cardinalfish are carnivores that feed on small planktonic and benthic crustaceans. In the aquarium this translates to meaty preparations such as mysis shrimp, brine shrimp, and finely chopped krill. Many specimens will also learn to take high quality flake and pellet foods once they are confident and eating alongside their group, though frozen items generally elicit the most reliable response from newly introduced fish.

Feed small portions two or three times daily so that every member of the shoal gets its share, and observe closely during the first weeks to confirm that shy individuals are actually eating. Cardinalfish possess a surprisingly large mouth and a healthy appetite for their size, so account for their intake when calculating rations for the rest of the tank. Insufficient food can also provoke squabbling within the group, making consistent feeding as much a behavioral issue as a nutritional one.

Mysis Shrimp Brine Shrimp Krill Marine Flake Food Marine Pellets
Shy and docile by nature, the Glass Cardinalfish spends much of its time hovering in loose formation near shelter, drifting into open water to pick at food and retreating quickly when disturbed. Kept as a proper group in adequate space, the shoal is peaceful and stable. Crowding or underfeeding is the main trigger for friction, and in those conditions individuals may bicker among themselves.

Tankmates must be equally peaceful. Boisterous or predatory fish will intimidate this species into hiding permanently, and it will lose out at every feeding. It is reef safe and poses no threat to corals or clams, in fact favoring branching stony corals as cover. As with cardinalfish generally, a very small ornamental shrimp or a tiny fish could occasionally be taken, though this is rarely a meaningful concern in a well-fed display.

FAQ

Frequently Asked Questions

About the Glass Cardinalfish

  • How many Glass Cardinalfish should I keep together?
    Keep a group of five or more, and introduce all of them to the aquarium at the same time so no individual is left as a late arrival.
  • Is the Glass Cardinalfish safe for my reef tank?
    Yes, it is reef safe and even shelters among branching stony corals such as Acropora, although like other cardinalfish it may occasionally take a very small shrimp or fish.
  • What should I feed my Glass Cardinalfish?
    Offer meaty carnivore fare such as mysis shrimp, brine shrimp, and krill, with high quality flake and pellet foods accepted once the fish have settled in.