Giant FRESH-WATER Stingray! The giant stingray is one of the world’s largest freshwater fish, but it’s also cloaked in mystery. No one is sure how many giant stingrays are left, which habitats they prefer, or even if they ever venture into the ocean, where their more commonly known relatives dwell. These ancient fish, little changed over many millions of years, can reach 16.5 feet (5 meters) long and weigh up to 1,320 pounds (600 kilograms).