Abstract
The aim of this study was to investigate effects of dietary levels of histidine (His) and iron (Fe) on cataract development in two strains of Atlantic salmon monitored through parr‐smolt transformation. Three experimental diets were fed: (i) a control diet (CD) with 110 mg kg −1 Fe and 11.7 g kg −1 His; (ii) CD supplemented with crystalline His to a level of 18 g kg −1 (HD); and (iii) HD with added iron up to 220 mg kg −1 (HID). A cross‐over design, with two feeding periods was used. A 6‐week freshwater (FW) period was followed by a 20‐week period, of which the first three were in FW and the following 17 weeks in sea water (SW). Fish were sampled for weighing, cataract assessment and tissue analysis at five time points. Cataracts developed in all groups in SW, but scores were lower in those fed high His diets ( P P N ‐acetyl histidine (NAH), the latter showing a marked increase post‐smoltification ( P P P