Protein is a basic component of fish diets, both in terms of quantity and quality, and protein is also the most expensive feed component. Fishmeal provides an adequate balance of amino acids, but increasing demand and price, as well as uncertain supply, make it necessary to find alternative protein sources. Other diet components (carbohydrates or fats) should be used to supply energy because they are usually less expensive. The economic importance of protein for farmers is related to its expense as a feed ingredient.