ALBERT

Notes: The development of cataracts in Atlantic salmon, Salmo salar L., was studied in 16 groups of smolts fed diets differing in prooxidant (iron, copper, manganese) and antioxidant (vitamin E, vitamin C, astaxanthin) composition and lipid level for 23 weeks in sea water, using a 27--3 reduced factorial design. The seven dietary variables were systematically varied at low (requirement level and 150 g lipid kg−1) and high levels (below known toxic levels and 320 g lipid kg−1). A mean endpoint cataract incidence of approximately 36% was observed. High dietary levels of vitamin C and astaxanthin reduced cataract frequency, whereas high dietary lipid level, iron and manganese were associated with increased cataract frequencies. Considering the nutritional status of selected organs of the fish, only the status of ascorbic acid correlated negatively to cataract development (P 〈 0.05). The lens glutathione (GSH) status was not correlated to cataract frequency, nor statistically explained by the dietary variables. However, the study shows that balancing the diet with respect to pro- and antioxidant nutrients may significantly protect Atlantic salmon against development of cataracts. An incidence of reversible osmotic cataract observed at week 14 was positively correlated to plasma glucose concentration.

Notes: There has been an increasing number of reports on cataracts in Norwegian and international salmon farming. The present study was undertaken to examine physiological and nutritional conditions during an outbreak of cataracts observed in rapidly growing Atlantic salmon, Salmo salar L., smolt with emphasis on zinc status. During this study, the cataracts were classified as irreversible. The outbreak of cataracts was positively related to fish growth and negatively related to the condition factor of the fish. Zinc concentrations in liver, eye and plasma were recorded in fish with cataract and in healthy fish from December to May. Lower zinc status (around 20%) was found in fish with cataracts compared to healthy fish, both over time and with regard to severity of the cataract. The decline in organ zinc concentrations seems to be explained by increased relative liver size, lower dry matters in liver and eye, and lower plasma protein. From the present data, the incidence of cataracts could not be directly related to zinc or any of the other nutrients (vitamin A, iron) examined, although relative deficiencies caused by other unknown rearing factors cannot be excluded. The lower condition factor and differences in organ water composition in fish with cataracts indicate that the cataracts may be related to the smoltification processes. Smoltification in the fish population was most probably accelerated by elevated water temperatures.

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: The effect of fluctuation in water temperature during the freshwater rearing stage on cataract development in Atlantic salmon was investigated. Presmolts were exposed to either constant low or high temperatures, or high temperature with cold-water fluctuations. Temperature fluctuations caused the fastest growth rate and most severe cataracts, whilst low temperature resulted in slow growth and minor cataracts. The fish were then individually marked and maintained together in a seawater net pen for 7 months. Cataract progressed in all groups, fish from the low temperature group showed the fastest subsequent growth, and developed cataracts to the same degree as fish from the other groups. There were no statistically significant differences in selenium-dependent glutathione peroxidase levels in pooled samples of aqueous humour, lens and plasma from fish with or without cataract, except from the last freshwater samples, where cataractous fish showed lower plasma activity. Plasma cortisol and glucose levels did not differ, nor did whole eye riboflavin levels. Higher concentrations of some free amino acids in whole eyes were found in fish with cataract. This study shows that fluctuation in water temperature may cause both increased growth rate and cataract development in Atlantic salmon and that cataract development initiated in the freshwater rearing phase continues after transfers to seawater.

Notes: In the period from winter 1996 to autumn 1999, three feeding trials were conducted to study the possible role of mammalian blood meal in preventing lens opacities in Atlantic salmon. In addition to blood meal supplemented feed, experimental diets were formulated, aiming to mimic the total concentrations of selected elements present in blood meal (BM) enriched diets; the amino acid histidine (His) and the mineral iron (Fe). In addition, these diets were supplemented with Zn. The trials included different rearing conditions, sizes and strains of Atlantic salmon; one small scale feeding experiment with pre-smolt of Strain A in fresh water (Trial 1) and two semi large trials with sub-yearling (S0s) and yearling (S1s) smolts of Strains A and B in seawater (Trials 2 and 3). The trials included duplicate or triplicate feeding groups and lasted 6–12 months. Standard commercial diets not supplemented with BM were used as controls. High prevalence of cataract developed over time in all three studies, with end point ranges as follows; Trial 1: 40–52 %; Trial 2: 51–83 %; Trial 3: 63–100%. The cataracts normally first appeared in the anterior and/or posterior cortical region and later affected the perinuclear region. In all the experiments, there was a significant cataract preventative effect of both the BM supplemented and experimental diets compared to the respective control diets. To some extent, cataract incidence was reduced, but primarily cataractogenesis was less severe in these groups. A concurrent positive effect on growth of both added BM and experimental diets was observed in the two seawater trials, probably related to maintaining vision and feed uptake ability. In one of the trials, there were significant differences in cataract susceptibility between the two strains, measured both as frequency and severity of cataractous changes. Our data suggest that elevated concentrations of dietary His and/or Fe mitigate cataract formation.

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.