Vitamins are organic molecules that are essential for the normal development and maintenance of all organisms. They participate in a variety of metabolic processes. In fish, the minimum vitamin requirements depend on size, age, growth rate, diet etc. In intensive fish farming it is required that vitamins are added to feed, in the form of supplements, to ensure that the biological requirements of aquatic organisms are met and to prevent vitamin deficiencies. The supplementation of farmed fish with vitamins is suggested especially in high stress periods (before handling, vaccination, grading etc).