Freshwater fish may be either coldwater or tropical species. Although freshwater aquariums can be set up as community tanks, coldwater and tropical fish are generally not mixed due to incompatibilities in temperature requirements. Tropical freshwater aquariums house "warm water" fish such as cichlids, tetras and other species that require a heating apparatus. For a tropical fish tank, maintaining a warm environmental temperature ranging between 75 to 80 °F (24 to 27 °C) enables the fish to thrive.

The major families and species include: