Cardinal Tetra – Paracheirodon axelrodi

The Cardinal Tetra is a strikingly beautiful freshwater fish known for its vivid blue and red colouration. These small, schooling fish are a favourite among aquarium enthusiasts due to their peaceful nature and stunning visual appeal. Native to South America, they thrive in soft, acidic waters and do best in groups. With proper care, they can be a vibrant and active addition to a well-maintained aquarium.

Quick Overview

Common Names: Cardinal Tetra
Scientific Name: Paracheirodon axelrodi
Popularity: Very popular among freshwater fishkeepers
Adult Size: Around 2 inches (5 cm)
Lifespan: 3–5 years (can live longer with optimal care)
Sexing: Difficult; females tend to have a rounder belly when carrying eggs
Temperature: 73–81°F (23–27°C)
pH Range: 4.5–7.0
Water Hardness: Very soft to moderately hard (1-6 dGH)
Nature: Peaceful, schooling fish

Natural Habitat & Origin

The Cardinal Tetra is native to the Orinoco and Rio Negro river basins in South America. These blackwater rivers are rich in tannins from decaying leaves, creating soft, acidic conditions where the fish thrive in large schools among submerged roots and plants.

Appearance & Size

Cardinal Tetras have a vibrant neon-blue stripe from nose to tail and a striking red stripe along the lower half of their body. Unlike the similar Neon Tetra, their red extends the full length of the body. Juveniles are around 0.5 inches (1.5 cm) but grow to about 2 inches (5 cm) as adults.

Tank Requirements

Minimum Tank Size: 15–20 gallons for a small school (6+ fish)
Preferred Tank Setup: Well-planted with open swimming spaces
Substrate and Decorations: Dark, soft substrate (sand or fine gravel); driftwood, leaf litter, and live plants to mimic their natural habitat
Tank Mate Options: Other peaceful community fish like rasboras, small gouramis, corydoras, and dwarf shrimp
Avoid: Large, aggressive fish like cichlids, barbs, and bettas that may see them as prey

Water Parameters & Conditions

Temperature: 73–81°F (23–27°C)
pH Range: 4.5–7.0
Water Hardness: 1–6 dGH (very soft to moderately hard)
Filtration & Oxygenation: Gentle filtration (sponge or low-flow filter); well-oxygenated water
Lighting: Dim to moderate, mimicking their natural shaded environment

Diet & Feeding

Cardinal Tetras are omnivores that require a varied diet for optimal health.

Recommended Foods: High-quality micro pellets, flakes, frozen or live foods such as daphnia, baby brine shrimp, and bloodworms
Feeding Frequency: 2–3 times per day in small amounts

Behaviour & Compatibility

Cardinal Tetras are peaceful and social fish that thrive in groups of at least 6–10 individuals. They are best kept with other small, non-aggressive species.

Good Tank Mates: Ember tetras, harlequin rasboras, corydoras catfish, otocinclus, small gouramis
Avoid: Large, fin-nipping, or aggressive fish such as angelfish, tiger barbs, or large cichlids

Breeding

Breeding Cardinal Tetras in captivity can be challenging due to their specific water requirements. They require soft, acidic water (pH 4.5–6.0) and dim lighting to encourage spawning.

For successful breeding, set up a separate tank with dim lighting, very soft water, and fine-leaved plants to provide a suitable environment. Before spawning, condition the breeding pair by feeding them live or frozen foods for a few days to enhance their health and readiness.
During spawning, the female scatters eggs among the plants while the male fertilizes them. Once spawning is complete, remove the adult fish immediately, as they may eat the eggs. The eggs will hatch within 24 hours, and the fry will become free-swimming in about four to five days.
To support the growth of the fry, start feeding them with infusoria or liquid fry food. As they grow, gradually introduce baby brine shrimp to ensure they receive proper nutrition.

Common Health Issues & Prevention

Common health issues in fish include Ich (White Spot Disease), which can be prevented by maintaining stable water parameters. Fungal infections are another concern and can be avoided by ensuring clean water conditions. Nutritional deficiencies may arise if the diet lacks variety, so providing a well-balanced mix of foods is crucial. Additionally, as fish are sensitive to stress, it is important to acclimate them slowly to new environments to prevent shock.

Fun Facts

• Cardinal Tetras are often confused with Neon Tetras, but their red stripe extends fully from head to tail.
• They are found in blackwater rivers, which are stained dark by decaying plant matter.
• They glow under aquarium lighting, making them a favourite for planted tanks.
• Unlike some other tetras, they rarely nip fins, making them excellent community fish.
• Due to their sensitivity, they are not the best choice for beginners, but they thrive with proper care.