A public aquarium (plural: public aquaria or public aquariums) is the aquatic counterpart of a zoo, which houses living aquatic animal and plant specimens for public viewing. Most public aquariums feature tanks larger than those kept by home aquarists, as well as smaller tanks. Since the first public aquariums were built in the mid-19th century, they have become popular and their numbers have increased. Most modern accredited aquariums stress conservation issues and educating the public.