ALBERT

Notes: 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 〈 0.05). This effect was most pronounced when HD or HID was given in SW, but was also observed when these diets were given in FW only. Histidine supplementation had a positive effect on growth performance and feed conversion ratio (P 〈 0.05), whereas this did not occur when iron was added. Groups fed HD or HID had higher lens levels of His and N-acetyl histidine (NAH), the latter showing a marked increase post-smoltification (P 〈 0.05). The HD or HID groups also showed higher muscle concentrations of the His dipeptide anserine (P 〈 0.05). There was a strong genetic influence on cataract development in the CD groups (P 〈 0.001), not associated with tissue levels of His or NAH. The role of His and His-related compounds in cataractogenesis is discussed in relation to tissue buffering, osmoregulation and antioxidation.

Notes: This study was conducted to investigate protein synthesis rates and metabolism of histidine (His)-derivatives in lenses of Atlantic salmon (Salmo salar L.) of different dietary His background during parr–smolt transformation. Two populations of Atlantic salmon parr of equal origin were established in freshwater (FW), 3 months prior to transfer to seawater (SW). The populations were fed either a control diet (CD) containing 8.9 g kg−1 His or the same diet added crystalline His to a total level of 14.2 g kg−1 (HD). On the basis of these two populations, 14C His force-feeding studies were performed; in FW 3 weeks prior to sea transfer and in SW 6 weeks after transfer. The studies were conducted by force-feeding the respective diets enriched with 14C labelled His, with subsequent measurements of incorporation of 14C His into lens free amino acid pool, as well as into lens proteins and other free His pool fractions. The latter included the major lens imidazole N-acetylhistidine (NAH). Lens concentrations of His and NAH were clearly influenced by dietary His history, both in parr and smolt. The lens His and NAH concentrations in the CD population were considerably lower in SW than in FW, while in the HD group the His level was equal and the NAH level 50% higher in SW than in FW. Fractional synthesis rate for NAH, KS (NAH), in FW was 8.2 and 4.2 μmol g−1 day−1 for fish in the CD and HD populations, respectively. The corresponding KS (NAH) values in SW were 5.1 and 33.0 μmol g−1 day−1. Our data show that free His is rapidly converted to NAH in the lens, and that NAH seems to have a very high turnover, especially in salmon reared in SW. Fractional synthesis rate for lens proteins, KS (PROTEIN), ranged between 1.8 and 17.3% day−1 (182 and 2791 μg g−1 day−1, respectively), and was generally higher in SW than in FW (P 〈 0.01). In SW, KS (PROTEIN) was highest in fish in the HD population (P 〈 0.05), whereas lens protein retention in the HD group was significantly lower than the CD group (P = 0.01). In a second model assuming that His from lens NAH is available for protein synthesis, calculated values of KS (PROTEIN) ranged between 0.17% day−1 (17.6 μg g−1 day−1) and 0.48% day−1 (70.2 μg g−1 day−1). Cataract scores recorded in the His populations at a later point (day 204), showed that the CD fish had significantly higher mean cataract scores than individuals in the HD population (P 〈 0.01), confirming that low levels of lens His and NAH are associated with cataract development.

Notes: The present work was designed to study whether changes in dietary protein quality by means of partial inclusion of fish protein hydrolysate (FPH) would alter fish growth, feed utilization, protein retention and metabolism and fish health in general. FPH was produced after hydrolysing whole minced herring using the industrial enzyme Alcalase®. The dietary protein source, low-temperature-dried (LT) fishmeal nitrogen was exchanged with FPH nitrogen at six levels of inclusion ranging from 0 to 300 g kg−1. The experimental diets were fed to post-smolt (1+) Atlantic salmon (Salmo salar), with mean initial weight of 174 g for a period of 68 days. All diets were iso-nitrogenous, iso-energetic and contained the same amount of amino acids. Fish fed medium inclusion of FPH (180–240 g kg−1) showed a tendency to have higher feed intake than fish fed lower and higher levels of FPH inclusions. Significant higher individual specific growth rates were present in fish fed diets with 180 and 240 g kg−1 FPH when compared with those fed 300 g kg−1. Feed conversion ratio increased significantly (R2 = 0.61) and protein efficiency ratio decreased significantly (R2 = 0.59) in fish fed increased levels of FPH. Further, apparent digestibility of crude protein and the amino acids arginine, lysine, methionine and phenylalanine increased significantly with increased dietary inclusion of FPH. Plasma free amino acids, ammonium and urea indicated that FPH amino acids was absorbed earlier and nonsynchronously, and may thus be more prone to be catabolized than in those fish fed the less solubilized protein. FPH inclusion did not have an impact on fish health, as evaluated by haematology and clinical parameters.