Tetra fish are generally known for their peaceful nature and small size, and there are many different species of tetras with varying levels of hardiness. However, one of the toughest and most popular species of tetra is the Black Skirt Tetra (Gymnocorymbus ternetzi).
Black Skirt Tetras are hardy and adaptable, and can tolerate a wide range of water conditions. They are also relatively large for a tetra, growing up to 3 inches in length, and are known for their striking black and silver coloration.
While Black Skirt Tetras are generally peaceful, they can become nippy towards other fish if they feel threatened or stressed. As such, they are best kept in schools of 6 or more and provided with plenty of hiding places and territory to reduce stress and aggression.