Koi (and goldfish) have been kept in decorative ponds for centuries in China and Japan.
Fish have been raised as food in pools and ponds for thousands of years. Brightly colored or tame specimens of fish in these ponds have sometimes been valued as pets rather than food. Many other cultures kept fish for both functional and decorative purposes. Ancient Sumerians kept wild-caught fish in ponds, before preparing them for meals. Depictions of the sacred fish of Oxyrhynchus kept in captivity in rectangular temple pools have been found in ancient Egyptian art.
Similarly, Asia has experienced a long history of stocking rice paddies with freshwater fish suitable for eating, including various types of catfish and cyprinid. Selective breeding of carp into today’s popular and completely domesticated koi and goldfish began over 2,000 years ago in Japan and China, respectively. The Chinese brought goldfish indoors during the Song Dynasty to enjoy them in large ceramic vessels.
In Medieval Europe, carp pools were a standard feature of estates and monasteries, providing an alternative to meat on feast days when meat could not be eaten for religious reasons.
Marine fish have been similarly valued for centuries. Wealthy Romans kept lampreys and other fish in salt water pools. Tertullian reports that Asinius Celer paid 8000 sesterces for a particularly fine mullet. Cicero reports that the advocate Quintus Hortensius wept when a favored specimen died. He referred to these ancient fishkeepers as the Piscinarii, the “fish-pond owners” or “fish breeders.”
According to Sea World (which actually is more a scientific place then an entertainment center) the earliest public aquariums was in 1853 in London’s Regent Park. The aquariums kept going bust because the fish would die since they didn’t know much about filtration or heating at the time. Three years later P.T. Barnum opened the first one in America. Maybe that is what he really meant when he said “There’s a sucker born every year!”.