Some of the by-products of fish include the following except

The by-product of fish that is not on the list is "leather." Fish can be a valuable source of various by-products that are useful in various industries. For example, fish can be processed into fish meal, which is a high-protein feed ingredient used in animal feed production. Fish oil is another by-product that is commonly extracted from fish, which has a wide range of applications in the food, pharmaceutical, and cosmetic industries. Fish silage is another by-product that is produced when fish waste is ensiled, which can then be used as a fertilizer or feed ingredient. However, leather is not a by-product that is typically associated with fish. Leather is usually made from the skin or hide of animals such as cows, sheep, and goats. Therefore, leather is not a by-product of fish. In summary, while fish can be processed into a range of useful by-products like fish meal, oil, and silage, leather is not one of them.