Histidine nutrition and genotype affect cataract development in Atlantic salmon, Salmo salar L.

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

Atlantic salmon (Salmo salar) postsmolts adapt lipid digestion according to elevated dietary wax esters from Calanus finmarchicus

Wax esters in copepods constitute huge natural marine lipid resources, which can contribute as future lipid source in formulated diets in aquaculture, and thereby reduce the pressure on use of marine resources at higher trophic levels. The present study was undertaken to investigate factors affecting wax ester digestibility, including production of bile and lipases, in Atlantic salmon fed diets containing high proportions of an oil derived from copepods. Individually tagged postsmolt Atlantic salmon (initial weight 250 g) were distributed into three dietary groups in triplicate tanks and fed either a fish oil supplemented diet, or diets where 50% or 100% of the fish oil was replaced with oil extracted from Calanus finmarchicus. Wax esters accounted for 307 or 477 g kg-1 of the lipids in these latter diets, respectively. Over the 100 day feeding period, the salmon fed the fish oil diet displayed a significantly higher specific growth rate (SGR; 0.74) than fish fed the 100% Calanus oil diet (SGR; 0.67). The apparent digestibility coefficient of total lipid and total fatty acids was significantly higher in salmon fed the fish oil and the mixed diet than in fish fed the pure Calanus oil diet. However, the fish appeared to adjust lipid digestibility to the increased intake of wax ester by enhancing bile volume and the lipolytic activity. The study indicates that Atlantic salmon show adaptations in digestion to elevated dietary wax ester intakes, however with an upper limit for optimal utilization in practical diets

The influence of temperature on the apparent lipid digestibility in Atlantic salmon (Salmo salar) fed Calanus finmarchicus oil at two dietary levels

Oils extracted from the marine zooplankton, Calanus finmarchicus, have high levels of n-3 highly unsaturated fatty acids (HUFA) and are therefore of interest as an alternative lipid source in aquafeeds. Copepod lipid is composed mainly of wax esters (WE) with high levels of saturated fatty acids and monounsaturated fatty alcohols which are considered hard to digest, especially at low temperatures. This assumption has however not been verified and for this reason the present study examined the digestibility of diets containing high levels of WE and two fat levels in Atlantic salmon reared at 3 and 12 °C. The fish were acclimated for one month to 3 °C (485 g) and 12 °C (599 g) and then fed one of four diets, high fat fish oil (33% lipid, HFFO), high fat Calanus oil (32% lipid, HFCO), low fat fish oil (17% lipid, LFFO) and low fat Calanus oil (19% lipid, LFCO). The fish meal lipid content was lowered by the use of lipid-extracted fish oil (2.3% lipid). This enabled a level of 50% WE in the LFCO and HFCO oils, compared to 0% in the LFFO and HFFO diets. The fish were then allowed to grow to around 100% of initial weight (220 days at 3 °C and 67 days at 12 °C) and then analysed for faecal lipid digestibility, bile volume, bile composition and intestinal lipolytic activity. Differences were observed in all these parameters in relation to temperature, type of dietary oil and the lipid level in the diet. Faecal lipid content and lipid class composition were dependent on rearing temperature and the type of dietary lipid. Highest levels of undigested lipids were observed in the faeces of fish fed CO. Wax ester-derived fatty alcohols, particularly 20:1n-9 and 22:1n-11, were less extensively digested than corresponding fatty acids from FO at both fat levels and temperatures. Fish kept at 12 ºC had a significantly higher bile volume than fish at 3 ºC and higher volumes were found in fish fed CO diets compared to FO. Decreased faecal passage time at lower temperatures, was not sufficient to ensure high digestibility since the lower bile volume and enzyme activities at 3 °C in the present trial exerted a greater effect. Although the compensatory mechanisms of increased bile volume and lipolytic activity are initiated upon feeding WE at a level of 50% of dietary lipid, these are not sufficient to compensate lipid digestibility and growth as in FO diets. Low inclusion of CO in diets during winter has to be considered as saturated fatty acids and monounsaturated fatty alcohols were poorly digested at 3 °C in fish fed CO diets

Role of histidine in cataract formation in Atlantic salmon (Salmo salar L).

Elevated levels of dietary histidine have been shown to reduce cataract formation in farmed Atlantic salmon. The aim of this study was to explore the possible roles of histidine and its derivatives in the lens. Since histidine is a buffer at physiological pH, its contribution to lens buffering capacity was examined. In addition, the role of histidine and its analogues in lens osmoregulation was investigated

Pre and postprandial regulation of ghrelin, amino acids and IGF1 in Atlantic salmon (Salmo salar L.) at optimal and elevated seawater temperatures

Atlantic salmon farmed in seacage facilities are exposed to changing environmental conditions. While growth decline under lower water temperatures are reasonably well understood, the mechanisms behind production decline under high water temperatures are yet to be well elucidated and have been hampered by a lack of data describing pre- and postprandial patterns of endocrine fluctuation. The present research therefore aims to determine whether peak nutrient flux into the blood plasma is the most appropriate time point to investigate the endocrine regulation of growth and appetite under conditions of normal and high temperature, and to investigate the interrelationship between appetite and growth on a pre- and post-prandial time scale. Two experiments are presented which examine ghrelin (GHRL) as an indicator of appetite stimulation, the GH–IGF (growth hormone–insulin-like growth factor) system to describe growth-regulating processes and free amino acids (FAA) to indicate postprandial nutrient influx and link appetite and anabolic processes. Postprandial sampling of plasma and white muscle tissue from short-term adapted postsmolt was conducted at 13 °C and 19 °C at 4, 8, 12, 16, 20 and 24 hours (h). The same samples were taken from long-term adapted big salmon at 12 °C, − 4, − 2, − 1, 0 h pre-prandially and 2, 3, 4 and 6 h post-prandially. While limited relationship between plasma ghrelin concentration and meal times was found for short term adapted postsmolt, clear ghrelin peaks were described for long term adapted salmon prior to the timing of anticipated meals. Possible explanations and consequences to experimental design in this area will be discussed. Postprandial FAA in plasma and white muscle from postsmolt was reduced at 19 °C compared to 13 °C and plasma levels peaked 8 h post-prandially. Muscle Igf1 mRNA expression levels were consistently higher at 13 °C than 19 °C, with no clear postprandial patters. In contrast, plasma IGF-1 concentration was relatively constant over time at 12 °C and 13 °C, but significantly declined from 20 h postprandially at 19 °C. GH receptor (ghr1) mRNA expression in muscle was unaffected by temperature, peaking 4 h post-prandially at both temperatures. This paper describes growth and appetite-regulating processes under conditions of normal and elevated temperature for Atlantic salmon, which is fundamental to our understanding of growth limitations inherent to high water temperature situations

Triacylglycerol-, wax ester- and sterol ester-hydrolases in midgut of Atlantic salmon (Salmo salar)

Bile salt-dependent lipase (BSDL) is assumed to be the predominant lipid hydrolase in fish digestive tracts where it hydrolyses dietary triacylglycerols (TAG), sterol esters (SE) and wax esters (WE). BSDL is known to hydrolyse TAG at much faster rates than SE and WE in both fish and mammals. An assay for BSDL has previously been developed for rainbow trout (Oncorhynchus mykiss). However, this setup may not be valid in other fish species. Accordingly, the present study aimed at optimizing previous assays in rainbow trout for use on intestinal luminal contents of Atlantic salmon (Salmo salar L.). Crude intestinal extracts from midgut were desalted before the assay and concentrated bile salts supplemented. In general, the rank order for the degree of hydrolysis in Atlantic salmon was TAG > WE > SE. The optimal assay conditions were determined as being 100 lg protein, 125 lM lipid substrate and 20 mM bile salt (taurocholate) during the 4 h of incubation. Atlantic salmon and rainbow trout of 1500 g showed similar lipolytic activity, while salmon smolts of 300 g showed a significantly lower activity. Furthermore, the inhibition of intestinal lipase activities, especially triacylglycerol hydrolase and sterol ester hydrolase, observed in trout intestinal extracts at bile salt concentrations around 10 mM, was not observed in salmon. This could indicate that the activities in these two salmonids may display different enzyme biochemistry

Dietary histidine affects lens protein turnover and synthesis of N-acetylhistidine in Atlantic salmon (Salmo salar L.) undergoing parr-smolt transformation

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

The vitamin D receptor and its ligand 1{alpha},25-dihydroxyvitamin D3 in Atlantic salmon (Salmo salar),The vitamin D receptor and its ligand 1alpha,25-dihydroxyvitamin D3 in Atlantic salmon (Salmo salar)

Contains fulltext : 36618.pdf ( ) (Closed access)Seaward migration of Salmo salar is preceded by preparatory physiological adaptations (parr-smolt transformation) to allow for a switch from freshwater (FW) to seawater (SW), which also means a switch in ambient calcium from hypocalcic (<1 mM Ca(2+)) to the plasma (~1.25 mM Ca(2+)) and to strongly hypercalcic (8-12 mM Ca(2+)). Uptake, storage (skeleton, scales) and excretion of calcium need careful regulation. In fish, the vitamin D endocrine system plays a rather enigmatic role in calcium physiology. Here, we give direct evidence for calcitriol involvement in SW migration. We report the full sequence of the nuclear vitamin D receptor (sVDR0) and two alternatively spliced variants resulting from intron retention (sVDR1 and sVDR2). In FW parr, SW adapting smolts, and in SW adults, plasma concentrations of 25(OH)D(3) and 24,25(OH)(2)D(3) did not change significantly. Plasma calcitriol concentrations were lowest in FW parr, doubled during smoltification and remained elevated in SW adults. Increased calcitriol coincided with a twofold decrease in sVDR mRNA levels in gill, intestine, and kidney of FW smolts and SW adults, when compared with parr. Clearly, there was a negative feedback and dynamic response of the vitamin D endocrine system during parr-smolt transformation. The onset of these dynamic changes in FW parr warrants a further search for the endocrines that initiate these changes. We speculate that the vitamin D system plays a crucial role in calcium and phosphorus handling in Atlantic salmon