Black tetra (Gymnocorymbus ternetzi) can be found in southern Brazil, Paraguay, Argentina, and as far west as Bolivia. This is a very popular freshwater aquarium fish. Wild specimens can be almost 3.5 inches long, but aquarium specimens usually grow to less than 2 inches. The silver body marked with two black vertical marks both ahead of the dorsal fin, and the somewhat dark dorsal and anal fins will help identify this species. Black tetras are hardy, and relatively easy to keep alive compared to many other species found in pet stores.

Characins, Family Characidae, is a family of freshwater fish that contains the Tetras, Piranhas, and many fish that are frequently kept as tropical aquarium fish. There are about 500 species in this family.

Order Cypriniformes contains the majority of the world's freshwater species of fish. Included in this order are the minnows, carp, and many other groups of fish.

Bony fish, Class Teleostomi, are a class of chordates that include the majority of fish-like animals found on earth. They are characterized by a bony jaw and a bony skeleton. They are found in both fresh and marine waters.

Backboned Animals (Phylum Chordata) are the most advanced group of animals on earth. These animals are characterized by having a spinal cord or backbone. Most members have a clearly defined brain that controls the organism through a spinal cord. Fish, amphibians, reptiles, birds, and mammals are in this phylum.

Currently, some taxonomists believe that the fish should be divided into two groups (sharks and regular fishes) and that there are some other primitive groups in the phylum such as hagfish or lampreys.

Animal Kingdom contains numerous organisms that feed on other animals or plants. Included in the animal kingdom are the lower marine invertebrates such as sponges and corals, the jointed legged animals such as insects and spiders, and the backboned animals such as fish, amphibians, reptiles, birds, and mammals.

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