Gub

As a noun: A "gub" refers to a fish. This can be any fish, but is used more for large fish, fish with big mouths, and/or fish that like to eat a lot. Sometimes other aquatic animals (shards, whales, etc.) can be referred to as such. The plural for "gub" is "gubs."
As a verb: The action of "gubbing" is for an aquatic animals (usually fish) when they pick at the bottom of either a tank or body of water in order to obtain food. "Gubbed," "gubbing," and "gub" are the past, present, and future tenses for this word.

As a noun: We went to the local aquarium and saw many large gubs.
As a verb: My pet fish gubbed at the bottom of the tank after they were fed.