Producers of fish feeds often approach nutrition with the attitude of “at least X” amount of nutrients in a feed. Diets will be said to contain at least 40% crude protein or at least 15% fat. While this is largely acceptable with macronutrients such as protein or fat, it can be an enormous issue with micronutrients like vitamins. This is particularly true in the fat soluble vitamins like Vitamin A which are accumulated within the fat stores of the fish rather than having any excess excreted.
Vitamin A has been shown in numerous flatfish species to be responsible for malpigmentation and skeletal malformations which can reduce the sale price of the animals or even cause mortality in extreme cases. Understanding how Vitamin A functions in these fish as well as safe limits for inclusion will make feeds better and help improve the flatfish industry.