We can call 'differentiated' or 'special feeds', those feeds whose formulation and composition differ from the feeds formulated traditionally and used more frequently. The demand for this kind of feed comes from the fish farmers, who want or need to differentiate their fish by using these special feeds. From the beginning of the Mad Cows Crisis, three years ago, the general psychosis and the doubt about the foods for human consumption, have brought about stricter control over their sources. This trend has been reinforced by the apparition of new crisis and polemics (dioxins, GMO). In Aquaculture this control, specially encouraged by the big supermarket chains, includes the fish-feed used on the farms. This requirement very often means removing the raw materials considered 'dangerous'. Also, these special feeds arose through the search of the fish farmer to voluntarily differentiate his product from the rest of the market.