Threadfin Cardinalfish

Care at a glance

Overview

Shy and docile, it does best in a peaceful tank with calm eaters and no boisterous competitors, since faster fish can intimidate it away from food. Reef safe with corals and invertebrates, it should be kept in a school of five or more so it feels secure enough to hover out in the open instead of hiding. Feed a varied diet of brine shrimp, mysis and other finely chopped meaty foods several times a day so the slower individuals in the group get their share.

In the wild

Native to the Indo-Pacific from the Red Sea and Mozambique to Samoa and Tonga, north to the Ryukyu Islands and south to New Caledonia, where it forms dense, mixed-species aggregations in sheltered lagoons and bays at depths of about 1–12 meters. A nano schooler best kept in a group of five or more, in at least 114 liters (30 gallons) with gentle flow, subdued lighting and plenty of coral branches or urchin spines for the school to hover around.

Good to know

The threadfin cardinalfish is a mouthbrooder that forms monogamous pairs within the school, with the male carrying the fertilized eggs in his mouth through incubation. Unlike most cardinalfish, which are nocturnal and hide alone or in loose pairs by day, this species stays active with its school around the clock, making it one of the few truly diurnal schooling cardinalfish in the trade.

Did you know

Its nearly transparent body helps it vanish into open water while schooling over reef flats during the day, a rare daytime strategy among cardinalfish, most of which rely on darkness and cave cover to stay safe instead.

Related species

• 

  Pajama Cardinalfish

  Sphaeramia nematoptera

  3.1 in (8 cm)29 gal (110 L)72–81°F (22–27°C)

• 

  Yellowstriped Cardinalfish

  Ostorhinchus cyanosoma

  3.1 in (8 cm)30 gal (114 L)72–79°F (22–26°C)

• 

  Orbiculate Cardinalfish

  Sphaeramia orbicularis

  3.9 in (10 cm)30 gal (115 L)75–82°F (24–28°C)

• 

  Banggai Cardinalfish

  Pterapogon kauderni

  3.1 in (8 cm)29 gal (110 L)73–82°F (23–28°C)

• 

  Flame Cardinalfish

  Apogon maculatus

  4.3 in (11 cm)30 gal (114 L)72–79°F (22–26°C)

• 

  Blue Assessor

  Assessor macneilli

  2.8 in (7 cm)29 gal (110 L)72–79°F (22–26°C)