AQUARIUM FISH is a widespread and popular hobby, and unlike earlier naturalists, modern aquarists have a great deal of highly technical equipment available and well over 100 years of expertise and experience to draw on. An immense variety of fish is available to the amateur aquarist. Tropical freshwater species are still the most popular, but cold-water aquarium fish like the goldfish, found in a great range of colors and forms, are also widely kept. Saltwater aquaria present more problems, but with the advances in equipment in recent years, tropical marine fish—plus organisms like anemones, prawns, and corals—can be kept by a skilled amateur. Cold-water marine species can be kept successfully, too, with the correct equipment. A well-maintained aquarium with a healthy community of fish and good growth of aquatic plants can provide hours of interest. In fact, observing fish in an aquarium often leads to the even more rewarding study of fish in their natural environment. AQUARIUM FISH, a title in the popular series Pet Library, is an illustrated, practical guide to animals we love so much that we make them part of the family.