A difficulty in keeping marine fish is providing them with seawater. Some aquarists have had success using preparations that are added to soft tap water or to distilled water to make synthetic seawater. Marine tropical fish need more water and water surface than do freshwater tropical fish. Marine aquariums are constructed in much the same way as freshwater aquariums. However, because seawater reacts with the chemicals contained in metals, paints, and cements, only all-glass tanks or tanks with frames made of stainless steel of a certain kind can be safely used. Any other materials that may come in contact with the water must be covered with water proof epoxy paints or with plastics.

Marine tropical fish can be fed approximately the same kind of feed suitable to freshwater varieties, except that they need larger proportions of live or freeze-dried animal feed, such as brine shrimp. Little is known about diseases of marine fish, but the preventive measures used with freshwater tropical fish have proved successful. Some diseases of marine tropical fish have responded to combinations of antibiotics.

Among marine fish suitable for home aquariums are angelfish, butterfly fish, dam-selfish, parrot fish, triggerfish, and sea horses.

Livebearers make up the family Poeciliidae. The guppy is Poecilia reticulata. Mollies are of the genus Mollienesia; platys and swordtails, of the genus Xiphophorus.

Cyprinids make up the family Cyprinidae. Genera of barbs include Puntius, Capoeta, and Barbodes; of danios, Danio and Brachydanio. Rasboras make up the genus Rasbora.

Characins make up the family Characidae. Genera of tetras include Hyphessobrycon, Hemigrammus, and Cheirodon; of pencilfish, Nannostomus and Poecilobrycon; of piranhas, Pygocentrus.

Labyrinth fish make up many different families. Genera of gouramis include Helostoma of the family Helostomatidae, and Colisa and Trichogaster of the family Belontiidae. The Siamese fighting fish is Betta splendens of the family Anabantidae; the paradisefish is Macropodus opercularis of the family Belontiidae; the climbing fish is Anabas testudineus of the family Anabantidae.

Cichlids make up the family Cichlidae. The jewel fish is Hemichromis bimaculatus; the butterfly cichlid, Apistogramma ramirezi.

Angelfish are of the families Pomacanthidae and Cichlidae; butterfly fish, Chaetodontidae; damselfish, Pomacentridae; parrot fish, Scaridae; trigger-fish, Balistidae; sea horses, Syngnathidae.