The Costello Tetra, also known as the January Tetra and scientifically known as Hemigrammus hyanuary, is a small, elegant species of tetra native to the slow-moving rivers, floodplains, and lakes of the Amazon Basin in Brazil and Peru. It is valued in the aquarium hobby for its peaceful temperament, attractive coloration, and ease of care, making it an excellent choice for community and planted aquariums.

Adult Costello Tetras typically reach about 1.5 to 2 inches (4 to 5 cm) in length. They have a slender, silver body with a faint golden to greenish iridescence along the flanks. The most distinctive feature is a bold black spot at the base of the caudal fin (tail), sometimes with a pale crescent-shaped band just before it. The dorsal and anal fins often have a faint reddish or orange tint, especially in males during breeding. Overall, the coloration is subtle but elegant, particularly in a well-planted, dimly lit tank.

A tank of at least 15 to 20 gallons is recommended for a small school. Costello Tetras are true shoaling fish and should be kept in groups of six or more to encourage natural schooling behavior and reduce stress. The aquarium should include soft sand or fine gravel substrate, driftwood, and plenty of live plants, as well as floating plants or leaf litter to diffuse the lighting and mimic their natural habitat.

Water parameters for the Costello Tetra should include a temperature range of 74 to 80°F (23 to 27°C), a pH between 5.5 and 7.0, and soft to moderately hard water. Regular partial water changes and gentle filtration are important for long-term health and coloration.

Feeding Hemigrammus hyanuary is easy, as they are omnivorous and will accept a variety of small foods. Offer high-quality flakes or micro pellets as a staple, and supplement with live or frozen foods such as daphnia, brine shrimp, and bloodworms.

Costello Tetras are peaceful and do well in community tanks with other small, non-aggressive fish such as other tetras, rasboras, Corydoras, pencilfish, and dwarf cichlids. Avoid keeping them with large or aggressive tankmates.

Breeding the Costello Tetra in captivity is possible but rarely attempted. They are egg-scatterers and show no parental care. To breed them, use a separate tank with soft, acidic water, spawning mops, and fine-leaved plants. Remove adults after spawning to prevent egg predation.

Hemigrammus hyanuary (Costello Tetra, January Tetra) is a peaceful, subtle species that brings schooling activity and understated beauty to South American and community aquariums.