The composition (fat, moisture and protein) of the fish flesh influences the physical and organoleptic properties of the final product. This text resumes the main basic principles affecting the composition of the fish body. Contrary to normal thinking, nutritional factors have a limited influence over the final composition of fish. Besides this, new alternatives on fish feed formulations are arising due to the present global situation of its raw materials, such as fish oil and fishmeal. New feed composition has to be adapted with efficiency but paying attention to its influence on the organoleptic parameters of the fish flesh.