Neon and Cardinal Tetras are similar in appearance and are often confused with each other. However, there is one very easily identifiable difference. In the Cardinal Tetra, the red stripe on the lower half of the body extends the full length of the fish from the eye area to the tail. In the Neon Tetra, the red stripe starts at mid-body, roughly below the dorsal fin, and extends to the tail.
Neon Tetras have been in the aquarium trade longer than Cardinal Tetras and are usually the less expensive of the two species. They are also a bit smaller than Cardinal Tetras, rarely reaching an adult size of more than 1 inch. Neon Tetras do best in soft acidic water with a pH of 6.0 to 6.5 and a hardness level of 5 to 10 dGH. Neons are schooling fish and should always be kept in groups of five or more.
Cardinal Tetras have surpassed Neons in popularity and are in high demand in the aquarium trade. As a result, they are often priced a little more highly than their smaller and less brilliant cousins. Although they prefer soft acidic water, as the Neons do, Cardinals are more demanding, preferring a pH below 6 and a hardness level below 4 dGH. Adult Cardinals will reach a length of nearly 2 inches. Like Neons, they are best kept in schools of five or more.
Origin and Distribution
Both Neon and Cardinal Tetras originate from South America, although most of them sold today are bred in captivity by commercial breeders. Captive-bred fish tend to be more tolerant of water parameters than their wild-caught counterparts.
Wild Neon Tetras are found in clearwater and blackwater Amazon tributaries in Brazil, Columbia, and Peru. Today, most Neons in the trade are bred in Hong Kong, Singapore, and Thailand. More than 1.5 million Neon Tetras are imported to the United States every month, while fewer than 5 percent of Neons sold are caught in the wild in South America.
Wild Cardinal Tetras are found in the slow-moving waters of the upper Orinoco and Negro Rivers in South America. They have also been seen in other areas, such as Manaus, in northern Brazil, although these fish likely originated from specimens that escaped from collectors.
The natural habitat of Neon Tetras includes dark water and dense vegetation and roots. They favor lush plant life and hiding places with low light, including rocks and driftwood. Driftwood also has the effect of darkening and softening the water. In the tank environment, you can replicate the Neon's natural habitat with a dark substrate, driftwood, plenty of plants (including some floating plants, if possible), and perhaps a dark background at the sides and rear of the tank.
Cardinal Tetras in the wild also tend to stay in low light but prefer clear water that is standing or slow-moving. In the tank environment, provide for subdued lighting with floating plants and dark substrate, décor, or background. Cardinals need some places to hide but also should have an open area for swimming. Arranging plants around the outsides of the tank while leaving the center open usually works well.
Getting Tetras Started
Both Cardinal and Neon Tetras are very sensitive to overall water quality as well as pH and hardness. For that reason, they should not be introduced to a newly set-up aquarium, where changes in water parameters are inherent during the break-in period. To ensure success, wait until the aquarium has been well established and the proper water chemistry is in place before investing in these attractive but sensitive fish.
Neon Tetra (Paracheirodon innesi). U.S. Fish & Wildlife Service.