Fish

Fish are a type of monster that appear on the 22nd and other floors' lakes and can only be found from fishing.

In order to catch a fish, a player needs to meet the prerequisite in fishing skill, which differs for each fish and lakes. The lake near Kirito's log house contains the "local-god" fish, making it the the most difficult lake for fishing.

Aincrad Arc
Kirito and Asuna's house is located on the 22nd floor after they married. The former wanted to fish, but unknowingly, the lake he was fishing in had a monster, the local god fish, so he was not able to catch any fish. Later, an old man, an experienced fisherman, helps him out. With that, Kirito helps fish out and defeat the monster of the area.