In the Animal Crossing series, fish can be placed in the player's house as furniture. When placed, they come in their own fish tank. In early games, fish tanks are nearly identical. Starting in City Folk, tanks display more detail, with substrates ranging from sand and gravel to dirt. There is no tank variation based on the value of the fish inside, unlike bug cages, where lid color varies.
There are three sizes of fish tank: 1x1 (small fish), 2x1 (large fish) and 2x2 (very large fish). Only the smallest fish tanks (1x1) can be placed on tables, except in City Folk. Instead of a tank, goldfish swim in a blue-rimmed bowl. Seahorses and sea butterflies live in a small, cylindrical tank that the player can place on tables.