Fishkeeping is a popular hobby, practiced by aquarists, concerned with keeping fish in a home aquarium or garden pond. There is also a piscicultural fishkeeping industry, serving as a branch of agriculture.
An aquascaped freshwater aquarium
Koi (and goldfish) have been kept in decorative ponds for centuries in China and Japan.
Neon tetras are common freshwater fish kept as pets.
A 335,000 U.S. gallon (1.3 million litre) aquarium at the Monterey Bay Aquarium in California displaying a simulated kelp forest ecosystem
A fish is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits. Fish can be grouped into the more basal jawless fish and the more common jawed fish, the latter including all living cartilaginous and bony fish, as well as the extinct placoderms and acanthodians. Most fish are cold-blooded, their body temperature varying with the surrounding water, though some large active swimmers like white shark and tuna can hold a higher core temperature. Many fish can communicate acoustically with each other, such as during courtship displays.
Fish
Dunkleosteus was a giant Devonian armoured placoderm, c. 400 mya.
Largest: whale shark
Smallest: e.g. P. progenetica