The largest animal found in the ocean is the blue whale (Balaenoptera musculus). This magnificent mammal can grow up to 100 feet (30 meters) long and weigh as much as 200 tons or more, making it not only the largest animal in the ocean but also the largest animal known to have ever existed. Blue whales primarily feed on tiny shrimp-like animals called krill, consuming up to 4 tons of them each day during feeding season. Despite their size, blue whales are known for their gentle nature and are not a threat to humans.