Scientists are learning more each day about fish’s surprising mental capacity including multiple documentation of tool use. Fish can also be trained to do tricks people normally assume only mammals and birds can learn. Take, for example, Comet the goldfish. Granted, the sort of leaning exhibited in the video below is nothing more than operant conditioning via positive reinforcement; Comet really isn’t playing soccer but rather learning anthropomorphic behavior that earns it food. However, this is no different than how most animals (including dogs) are trained.
R2 Fish School (created by the owner of Comet) actually sells a goldfish training kit for aquarist who are interested in teaching their goldfish these tricks. To prove Comet isn’t a special genius-level one-of-a-kind, here is another (really cute) Shukin goldfish trained to do similar tricks using R2 Fish School.