Threadfin Cardinalfish

The Threadfin Cardinalfish is a delicate and ethereal-looking species that brings a unique translucent beauty to the marine aquarium. Its slender, semi-transparent body has a pale silvery-blue base coloration accented by fine horizontal blue streaks along the body and a subtle orange to pinkish tint on the fins. The elongated filaments on the dorsal and caudal fins give the species its common name and add an elegant, flowing quality to its silhouette. Large, dark eyes dominate the head, reflecting the species' primarily nocturnal activity pattern.

In the wild, the Threadfin Cardinalfish is one of the most abundant reef cardinalfish species, found in vast aggregations among branching corals, sea urchin spines, and sheltered overhangs throughout the Indo-Pacific. Schools numbering in the hundreds gather in the protective embrace of Acropora thickets and black sea urchins during the day, dispersing at night to feed on zooplankton in the water column above the reef. This schooling behavior is one of the species' most appealing features in the aquarium, where a group of Threadfin Cardinalfish creates a mesmerizing, constantly shifting cloud of silvery-blue fish hovering among the rockwork.

The Threadfin Cardinalfish is an excellent choice for beginners seeking a peaceful, reef-safe fish that displays natural schooling behavior in the aquarium. It is hardy, adapts quickly to captivity, and coexists peacefully with virtually all other reef inhabitants. Unlike the Banggai Cardinalfish, which can be aggressively territorial toward conspecifics, the Threadfin Cardinalfish is genuinely gregarious and should ideally be kept in groups of five or more to display its natural schooling behavior. Its small size and peaceful demeanor make it suitable for nano and small reef tanks, where a school creates an impressive visual display disproportionate to the fish's modest individual size.