Sucker, any of various freshwater fishes (family Catostomidae) related to the minnows. Most suckers live in North America, but there are a few in Asia. They have thick lips and feed by sucking food from the bottoms of lakes and rivers. Some suck up mud and eject inedible matter, while others turn over pebbles and suck the animals attached to the underside. A few have hard lips for scraping rocks.