Sewin is a type of trout that is commonly found in the rivers and streams of Wales. It is also known as sea trout or white trout. Some synonyms for Sewin include Salmo trutta, Salmo trutta morpha trutta, Cornish sea trout, and estuarine trout. Salmo trutta is the scientific name for this fish species. Cornish sea trout is a name for Sewin that is specific to the Cornwall region in England. Estuarine trout is a term used to describe Sewin and other trout that spend part of their life cycle in both fresh and salt water environments. Regardless of what you call it, Sewin is a prized catch for anglers and a delicious menu item for seafood lovers.