Freshwater Fish
Cardinal Tetra
The more vivid, full-length cousin of the Neon Tetra -- the blue stripe and red underside run the entire length of the body, producing a more dramatic and more complete colour display in every individual.
Cardinal Tetras (Paracheirodon axelrodi) are closely related to the Neon Tetra but display a more complete and more vivid colour pattern -- the iridescent blue stripe runs the full length of the body from head to tail, and the vivid red underside covers the entire lower half of the fish rather than only the rear portion as in Neon Tetras. The result is a bolder, more saturated, and more symmetrical colour display that many hobbyists consider superior to the Neon Tetra for planted tank display. Native to the blackwater tributaries of the Rio Negro and Orinoco in South America, Cardinal Tetras prefer soft, acidic water that aligns closely with Caridina shrimp parameters, making them one of the most natural fish companions for a Caridina planted tank. They are peaceful, schooling fish requiring groups of 10 or more, and their colour is most vivid in soft, warm, tannin-stained water with subdued lighting.
4.5–7.0pH
1–8GH (dGH)
73–81°FTemperature
2 inMax Size
Appearance & Schooling
Full-Length Stripe and the Cardinal Advantage
The blue stripe and red underside run the full length of the body -- the key distinction from the Neon Tetra. In a Neon Tetra the red colouration begins at the middle of the body and covers only the rear half. In the Cardinal Tetra the vivid red extends from the chin to the base of the tail, covering the entire lower half of the fish. The blue iridescent stripe similarly runs the complete length from the eye to the tail. This gives every individual a more complete and more dramatic colour display -- the full-body coverage means the fish reads as vivid at any angle rather than only from the rear.
Colour is most vivid in soft acidic water with tannins and subdued lighting. Cardinal Tetras originate from blackwater environments stained with tannins from decaying leaf litter. In water that replicates these conditions -- soft, acidic, warm, with some tannin presence from Almond Leaves or driftwood -- the iridescent blue stripe achieves its greatest intensity and the red underside its deepest saturation. In bright, hard, alkaline water the colour fades noticeably and the fish show more stress.
School of 10 minimum, 15 or more strongly recommended. Cardinal Tetras are obligate schooling fish and show colour loss, hiding, and stress in small groups. In a school of 15 or more they swim in tight formation and the collective shimmer of blue and red moving through planted greenery is one of the most impressive displays achievable in a freshwater aquarium. Larger schools also produce tighter, more synchronised schooling behaviour that adds visual dynamism the fish cannot produce alone.
Slightly larger and somewhat more temperature-sensitive than Neon Tetras. Cardinal Tetras reach approximately 2 inches at maturity, slightly larger than Neon Tetras. They prefer warmer water at 76 to 81°F and are less tolerant of the cooler end of the temperature range than Neon Tetras. They do not thrive at the cool temperatures preferred by White Cloud Mountain Minnows or Peppered Cories.
Shrimp Compatibility
Natural Partner for Caridina Tanks
Parameter overlap with Caridina shrimp is near-perfect -- one of the best fish pairings for a Caridina planted tank. Cardinal Tetras prefer pH 4.5 to 7.0 and very soft water, which aligns closely with the Caridina parameter range of pH 5.8 to 6.8 and GH 4 to 6. A well-established Caridina tank running RO water with active substrate and a temperature of 74 to 78°F is simultaneously close to ideal for a school of Cardinal Tetras. No parameter compromise is required between the two species.
Adult Caridina and Neocaridina shrimp are safe -- shrimplets are at moderate risk. Cardinal Tetras are mid-water to upper-water swimmers and are not aggressive substrate hunters. Adult shrimp at full size are too large to be targeted. Shrimplets in their first week are small enough to be consumed if encountered in open water. Dense planting with Java Moss, Subwassertang, and fine-leaved plants gives shrimplets the cover needed to survive to adulthood in a mixed tank.
The visual combination of Cardinal Tetras and Crystal Red or Crystal Black Shrimp is one of the most striking in the hobby. The vivid blue-and-red of the Cardinals moving through the mid-water above a colony of patterned CRS or CBS on dark substrate, in tannin-stained water with green planting, is a complete and intentional display that each species contributes to equally. The colour relationships between the species -- the red of the fish echoing the red of the CRS, the blue stripe counterpointing the white banding -- read as genuinely complementary.
Not ideal for hard-water Neocaridina setups at pH above 7.2. Cardinal Tetras can survive in neutral water but their colour fades and lifespan shortens in hard or alkaline conditions. For standard hard-water Neocaridina tanks, Neon Tetras or Celestial Pearl Danios are better-suited alternatives.
Keeper's NoteA school of 15 Cardinal Tetras in a blackwater-style Caridina planted tank with Almond Leaves, dark substrate, low flow, and subdued lighting is one of the most visually complete freshwater aquarium setups achievable at the hobbyist level. The tannin-stained water deepens the iridescent blue of the Cardinals to its most vivid expression, the Crystal Red Shrimp below are visible and active against the dark background, and the overall aesthetic -- warm, naturalistic, rich -- holds together as a unified display rather than a collection of individual elements. It takes patience to establish but is one of the most rewarding setups in the hobby once stable.
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