The cardinal tetra is probably the world’s favorite tropical fish in terms of numbers kept. Many hobbyists have at some point in time, kept cardinal tetras. And, while they have been bred, they have never been bred in commercial quantities. Therefore, millions of cardinals are caught wild and exported from Brazil every year. Dr. Labbish Chao has started a program called Project Piaba (piaba is the native name for little fish that swim with cardinals) to help educate collectors/exporters and improve the conditions under which the fish from Brazil are caught, conditioned and shipped to the world. Even though millions of cardinal tetras are caught every year, the fishery is managed very well. The fish are not allowed to be caught during the breeding season or shortly thereafter, and the Amazon/Rio Negro area is so vast that fishermen do not go back to the same site for years, thus allowing the cardinals to replenish.
Keeping a cardinal in the home aquarium is very easy as long as two conditions are met. First, do not keep it with larger fish (such as angelfish or other large cichlids) that quite naturally look upon the cardinal as food. And second, the cardinal needs soft, acid water. Water may be adjusted by using reverse osmosis or deionized water, or putting a peat pillow into the filter. Once the pH starts getting above 6.8 and/or the hardness above 12 DH, the cardinal doesn't do well.
When given the water conditions it likes and kept in a tank without any predators, the cardinal will do spectacularly well. It will eat absolutely any food: flake, frozen, freeze-dried or live. It does not bother its tankmates. Like all schooling fish, the cardinal is best kept in groups of at least six or eight, and more if possible.