Cataracts make the eye lens become white and opaque, and can, in the worst case, lead to blindness in fish. Salmon have a greater need for histidine in order to prevent the development of cataracts than, for example, rainbow trout. Trials at NIFES have shown that 13.4 grams of histidine per kilo fish feed can prevent the development of cataracts in salmon.
Histidine must be added
Blood meal was previously used as an ingredient in fish feed and is naturally rich in histidine. After the outbreak of mad cow disease, it was prohibited to use animal by-products, including blood meal, in feed. The amino acid histidine was therefore added early during the sea phase to prevent the development of cataracts.
The amino acid histidine helps regulate the water balance in the eye lens of the fish, and it acts as an antioxidant helping to protect the lens from changes. Salmon require more histidine than the amount required for optimal growth in order to ensure good eye health and thereby good fish welfare and the production of robust fish.