Threadfin Cardinalfish: Peaceful and Most Impressive in Numbers

Threadfin Cardinalfish (Zoramia leptacantha)

Threadfin Cardinalfish (Zoramia leptacantha)

Walk by an LFS sales tank containing a few specimens of threadfin cardinalfish (Zoramia leptacantha), and you might not give them a second glance. Chromatically speaking, this species isn’t exactly a showstopper compared to some, especially when viewed in your average LFS environment. But don’t let this cardinal’s unassuming appearance fool you; it can make for an impressive display species when kept in groups.

Physical traits

Z. leptacantha is a diminutive fish, reaching only about 2.5 inches in total length. It’s laterally compressed and has two dorsal fins, the first fairly elongated relative to the second.

As mentioned, this species’ color is nothing to write home about (in case you’re one of those types who like to write home about the colors of fish). It’s semi-transparent to yellowish-silver overall with iridescent blue around the eyes as well as blue and yellow accents on the anterior portion of the body. However, there’s a subtle beauty to this fish that, when kept in aggregate can really add up to a striking visual statement.


In nature, Z. leptacantha feeds primarily on small benthic crustaceans. Good alternatives for aquarium specimens include mysids, finely chopped crustacean and mollusk flesh, frozen commercial formulations for small carnivores, high-quality small pellet foods, etc.

A group of threadfin cardinalfish schooling in a reef aquarium

A group of threadfin cardinalfish schooling in a reef aquarium


I’ve seen minimum housing recommendations as low as 10 to 20 gallons for this species, but my preference would be to go with a slightly larger tank, say around 30 gallons minimum, so you have the opportunity to keep a decent sized group and observe the species’ natural schooling behavior.

Also, Z. leptacantha is nocturnal by nature, so it’s a good idea to provide a good-sized ledge or cave that the group can refuge under/in during daylight hours, especially in intensely illuminated reef tanks. Aquarium specimens often acclimate to daytime feeding and activity, but the best viewing opportunities might be under more subdued lighting (e.g., moon lighting or transitional lighting mimicking dusk and dawn periods).


Threadfin cardinalfish saltwater aquariumZ. leptacantha is a very peaceful species, and any piscine tankmates must be similarly passive. Again, this is a schooling species by nature, and it’s among the few marine species that can—and should—be kept in groups (5 or more) in captivity.

As far as reef-friendliness is concerned, Z. leptacantha is ideal. In nature, this species forms dense aggregations among and above branching stony corals, so a group of these cardinals would make a great addition to a tank full of “sticks.”


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. They are also very easy to spawn as they spawned in my tank all the time. I am not sure how long they live but I only had them for bout 4 or 5 years. I am not sure how old they were when I got them but they are very cool and peaceful.
    Give them some live blackworms and their colors will light up, then they will spawn.

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