Cardinal Tetra

Cardinal Tetra (Paracheirodon axelrodi)

One of the most iconic and beautiful small tetras in the aquarium hobby, the Cardinal Tetra is renowned for its brilliant iridescent blue upper body and vivid red lower half. Native to the soft, acidic blackwaters of the Upper Orinoco and Negro River basins in South America, this species forms large, shimmering shoals in the middle water layers. Named after the legendary tropical fish expert, entrepreneur, and publisher Dr. Herbert R. Axelrod, it remains a staple for planted community tanks and Amazonian biotopes worldwide.

Key Features

• Maximum Size: 3.0 cm / ~1.2 inches SL.
• Appearance: Slender, elongated body with a striking horizontal division: a bright neon-blue stripe along the upper half and a deep, vivid red stripe along the lower half and anal fin. The colors intensify in healthy, well-maintained specimens. Males and females are similar, though females may appear slightly rounder when gravid.
• Fin Details: Typical tetra fin structure with soft, flowing fins that enhance the fish’s graceful schooling movement.

Aquarium Care

• Tank Size: Minimum 20 gallons for a school of 8–10+ (larger is better to allow natural shoaling behavior).
• Water Parameters: Soft, acidic tropical freshwater; 73–82°F (23–28°C), pH 4.0–6.0, low hardness (5–12°dGH). Excellent water quality with regular partial changes is essential. Use RO or rainwater with tannins (Indian almond leaves, driftwood, or peat) to replicate their natural blackwater habitat. Dim lighting and dense planting (or floating plants) help them feel secure.
• Diet: Omnivorous — readily accepts high-quality micro-pellets, flakes, and small live or frozen foods (brine shrimp, daphnia, bloodworm). A varied diet helps maintain their brilliant colors.
• Behavior: Peaceful, active schooling fish that thrives in groups. Best kept with other small, non-aggressive species. They may be shy or lose color if kept singly or in poor conditions. Breeding is possible but challenging in home aquariums; most specimens in the trade are sustainably wild-caught from their native range.

IUCN Status Least Concern (LC)

Add iconic neon-blue and fiery-red brilliance to your planted or blackwater aquarium with the beautiful Cardinal Tetra!