There are many types of fish that come in different sizes, colors, and speeds. People currently know about 25,000 types of fish, but there are likely another 15,000 types that have yet to be discovered. Fish eat a variety of foods including other fish, bugs, plants, and worms. The fastest fish can swim 70 miles per hour, the heaviest weighs 15 tons, and the longest sharks can reach 50 feet. The smallest fish is less than 1/3 of an inch long.