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Butylated hydroxyanisole (BHA) is a phenolic antioxidant that is used as a food additive, particularly in fats and oils, and it is also authorized as a feed additive in the European Union for all animal species with a maximum concentration of 150 mg kg−1 feed (alone or in combination with ethoxyquin and/or butylated hydroxytoluene). Information on the BHA levels in food of animal origin is scarce, as is literature on the transfer of BHA from feed to animal products. Consequently, the current feeding trial was conducted under realistic rearing conditions to determine the retention of BHA in Atlantic salmon ( Salmo salar) fillets. Four different concentrations of BHA in feed were tested (0, 48.5, 92.5 and 225 mg BHA kg−1 feed), and fish were sampled after 4, 8 and 12 weeks dietary exposure, and after a 2-week starvation period, which is representative of commercial salmon farming in Norway. The levels of BHA in salmon fillets were fairly dose dependent during the feeding period. A steady state in fillet residues was reached after 4 weeks of administration of BHA. After the 2-week withdrawal period, BHA was not detectable (<7 μg kg−1) in either fish fillets or livers. [ABSTRACT FROM AUTHOR]

An experiment with 2(7 − 3) reduced factorial design was conducted to study the biological effects of pro- and antioxidant micronutrients and lipid in Atlantic salmon. Vitamins C and E, astaxanthin, lipid, iron, copper and manganese were supplemented at high and low levels. For vitamins and minerals, high levels were chosen to be below the anticipated toxic level and the low levels were just above the requirement (vitamin C, 30 and 1000 mg kg−1; vitamin E, 70 and 430 mg kg−1; Fe, 70 and 1200 mg kg−1; Cu, 8 and 110 mg kg−1; Mn, 12 and 200 mg kg−1). For astaxanthin, the dietary levels were 10 and 50 mg kg−1 and for lipid, 150 and 330 g kg−1. The experiment was started with postsmolts (148 ± 17 g) and lasted for 5 months. The variation in micronutrients had only minor effects on growth, feed conversion and fillet quality, measured as lipid and astaxanthin deposition. High dietary lipid had a profound positive effect on growth and feed conversion but gave fillets nearly two times the fat content that was found in fish fed the low lipid diet. Astaxanthin deposition in the fillet was primarily affected by dietary astaxanthin with a positive effect of high dietary lipid in week 14 but not in week 23. Vitamin E protected the fillet against iron ascorbate stimulated oxidation, with no effect of the other nutrient variables. [ABSTRACT FROM AUTHOR]

Abstract 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. [ABSTRACT FROM AUTHOR]

Sixteen groups of post smolt, Atlantic salmon (Salmo salar) (initial weight 148 ± 17 g) were fed diets with different lipid content and composition of pro- and antioxidants (vitamin E, vitamin C, astaxanthin, Fe, Cu and Mn). The composition of the experimental diets was based on a multivariate reduced factorial design (RFD) (27–3) with either high (+1) or low (–1) level (within limits of toxicity and requirement) of each of the seven dietary variables. Lipid class and fatty acid (FA) composition was analysed in retina, very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL). Further FA composition was analysed in fillet, liver and plasma. High dietary lipid increased growth, feed efficiency, fillet lipid level and the amount of LDL and HDL in plasma, whereas high dietary copper and high dietary vitamin E decreased the amount of plasma LDL. High dietary vitamin E decreased the amount of lipid and protein in LDL, whereas high dietary lipid increased cholesterol and cholesterol ester levels in plasma and HDL and the amount of lipid in LDL. Dietary astaxanthin and manganese affected retina PE levels. The FA composition did not differ significantly between the 16 diets. Dietary FA composition was reflected in fillet FA composition and gradually less in VLDL, LDL, HDL, plasma, liver and retina FA composition. Dietary lipid content influenced FA composition to some extent in the analysed tissues, i.e. generally high dietary lipid content led to a decreased relative amount of saturated and monoene fatty acids and an increase of the relative amount of polyene fatty acids. [ABSTRACT FROM AUTHOR]

Abstract Atlantic salmon smolt (64 g) were fed 40, 300 or 1100 mg kg[sup -1] all-rac-α-tocopheryl acetate feed under normoxic and moderate hyperoxic conditions for 12 weeks. After 7 weeks, however, the hyperoxic fish were subjected to a temporary severe supersaturation of dissolved oxygen with development of gas bubble disease and substantial mortality as a result. Liver α-tocopherol (α-TOH) levels reflected the dietary input after 6 and 12 weeks of feeding. Increased levels of thiobarbituric-reactive substances (TBARS) in the liver of hyperoxygenated fish after 6 weeks indicate that moderate hyperoxic conditions may represent an oxidative challenge to the fish. After 12 weeks, liver ascorbic acid (AA) content was reduced in hyperoxygenated fish, and a decreasing tendency was also found in the liver content of α-TOH. Effects of oxygen supersaturation were also observed on liver antioxidant enzyme activities, content of glutathione and total mercapthans in liver, phagocytic chemiluminescent response and total plasma protein level, indicating a disturbed redox balance. No effects of dietary vitamin E were observed on any of the measured parameters, indicating that high levels of dietary vitamin E under these circumstances did not protect the fish against oxidative stress. [ABSTRACT FROM AUTHOR]

Abstract The influence of α-tocopheryl acetate (α-TOAc) on plasma concentration and fillet deposition of dietary astaxanthin was investigated in Atlantic salmon Salmo salar L. The diets were added 30 or 50 mg kg[sup –1] astaxanthin, and 200, 400 or 800 mg kg[sup –1] α-TOAc at each astaxanthin level. Improved flesh deposition of astaxanthin by 8–14% was achieved for fish fed diets with 30 and 50 mg kg[sup –1] astaxanthin, respectively, by the dietary addition of 800 compared with 200 mg kg[sup –1] α-TOAc. These results were supported by CIE[1976]L*a*b* tristimulus redness measurements (a* value). Plasma astaxanthin concentration mirrored the muscle astaxanthin concentration in the groups of fish fed a diet containing 30 mg kg[sup –1] astaxanthin. The salmon fed a high astaxanthin and low α-TOAc diet had the highest plasma concentration of idoxanthin (P < 0.05). Astaxanthin retention was significantly higher (P < 0.001) in salmon fed 30 mg kg[sup –1] astaxanthin than in those fed 50 mg kg[sup –1] astaxanthin, but was not significantly affected by dietary α-TOAc. Liver weight, body weight, specific growth rate, feed/gain ratio and mortalities were not affected by dietary α-TOAc levels. In conclusion, the dietary addition of α-TOAc appears to increase astaxanthin fillet deposition in salmonids and may reduce the demand for astaxanthin supplementation. The effect was rather small and requires verification. [ABSTRACT FROM AUTHOR]

The minimum requirement of vitamin E for Atlantic salmon, Salmo salar L., at first feeding was found to be 60 mg dl-α-tocopheryl acetate per kg dry diet. The dry diet contained 5.6% polyunsaturated fatty acids, which is similar to that used in practical diets at first feeding. Preliminary results indicate that the optimal dietary vitamin E level is 120 mg dl-α-tocopheryl acetate per kg dry diet, or more. Further research is necessary to confirm this hypothesis. [ABSTRACT FROM AUTHOR]

The loss of fish in the seawater (SW) phase of Atlantic salmon farming is high, and a major proportion of this loss occurs in the period just after SW transfer. In the current study, we hypothesize that improvements made to the diet during the freshwater (FW) stage affect fish growth, survival and robustness later in the SW stage. To test this, salmon parr were fed five experimental diets in FW at 12 °C. In addition to a commercial-like control diet, fish were fed a diet with changed FA composition aimed to be more like the natural feed of salmon in FW, a diet with increased concentrations of selected AA/N-compounds (methionine, lysine, threonine and taurine), a diet with increased concentrations of methionine and certain B-vitamins (folate, B 12 and B 6) and a final diet combining all of these potential improvements. At the time of SW transfer, the robustness of fish fed the different diets was tested by direct transfer to SW at three different temperatures (8, 12 and 16 °C, without prior acclimation), as well as transfer into open net pens, while fed on a common commercial diet. Growth and proximate composition of the fish did not differ between the diet groups. All diet groups seemed to handle transfer to SW well, and while SW transfer elicited a stress response in the fish, this was not significantly different between diet groups. Fish transferred to SW at 8 °C had higher mortality, reduced mucus layer and increased prevalence of scale loss and wounds, but this applied to all diet groups. Hence, direct transfer to SW at a lower temperature than the fish has been acclimated to cannot be recommended. At the two highest temperatures, there were some differences between the groups in the severity of cataracts. Apart from this, none of the health- or welfare related parameters measured showed any difference between the diet groups, indicating that the control diet was already sufficient. • High loss of farmed salmon after seawater transfer was attempted ameliorated by diet. • The proposed dietary improvements did not affect survival or growth. • The fish did not handle direct transfer from 12 °C freshwater to 8 °C seawater well. • High rearing temperature and probably dietary histidine affected cataract. [ABSTRACT FROM AUTHOR]

This study sought to investigate whether a "natural diet" (mimicking the fatty acid composition of freshwater aquatic insects eaten by salmon parr) during the freshwater (FW) life stage of pre-smolt Atlantic salmon (Salmo salar L.) affected red blood cells and gill fatty acid composition as well as eicosanoid metabolism in gill during smolting at different temperatures. Before being transferred to seawater (SW), salmon parr were fed with a modified (MO) diet containing vegetable oils (rapeseed, palm, and linseed oils) supplemented with eicosapentaenoic acid (EPA) and arachidonic acid (ARA) to completely replace the fish oil (FO). Fatty acid composition in red blood cells and gill tissues was determined before SW transfer and six weeks after. Additionally, the expression of genes associated with eicosanoid metabolism and Na+/K+-ATPase (NKA) activity in salmon gill was examined at different temperatures before SW transfer and 24 h after. The results showed the changes in fatty acid composition, including sum monounsaturated fatty acids (MUFAs), docosahexaenoic acid (DHA), ARA, EPA, and sum n-6 polyunsaturated fatty acids (n-6 PUFA) in both red blood cells and gill tissues at the FW stage were consistent with the fatty acid profiles of the supplied MO and FO fish diets; however sum EPA and DHA composition exhibited opposite trends to those of the FO diet. The proportion of ARA, EPA, and n-6 PUFA increased, whereas sum MUFAs and DHA decreased in the red blood cells and gill tissues of MO-fed fish compared to those fed with the FO diet at FW stage. Additionally, 5-lipoxygenase-activating protein (Flap) expression was downregulated in MO-fed fish prior to SW transfer. During the process of SW transfer at different temperatures, the MO diet remarkably suppressed NKAα1a expression in MO-fed fish both at 12 and 16 °C. The MO diet also upregulated phospholipase A2 group IV (PLA2g4) expression in gills at 8, 12, and 16 °C, but suppressed phospholipase A2 group VI (PLA2g6) expression in gills at 12 °C compared to FO-fed fish at 12 °C and MO-fed fish at 8 °C. The MO diet also upregulated Cyclooxygenase 2 (Cox-2) expression at 8 °C compared to FO-fed fish and increased Arachidonate 5-lipoxygenase (5-Lox) expression in MO-fed fish at 16 °C compared to both FO-fed fish at 16 °C and MO-fed fish at 8 °C. Our study also determined that both SW transfer water temperatures and diets during the FW period jointly influenced the mRNA expression of PLA2g4 , PLA2g6 , and Lpl , whereas 5-Lox was more sensitive to dietary changes. In conclusion, the MO diet affected the fatty acid composition in gill and in red blood cells. When transferred to SW, dietary ARA supplementation could promote the bioavailability for eicosanoid synthesis in gill mainly via PLA2g4 activation, and potentially inhibit the stress and inflammatory response caused by different water temperatures through dietary EPA supplementation. • Salmon parr were fed with a MO diet only containing vegetable oils supplemented with EPA and ARA. • The MO diet affected fatty acid composition synergistically in gills and red blood cells at FW stage. • A lasting impact of MO diet during FW stage on fatty acid composition after SW transfer. • The MO diet promoted the eicosanoid biosynthesis in gill during SW transfer. • The MO diet inhibited the inflammatory response during smoltification at different temperatures. [ABSTRACT FROM AUTHOR]

The aim of the current study was to investigate how freshwater diets impact on immunity in Atlantic salmon smolts in freshwater, during transfer to seawater and in post smolts during the seawater stage with and without pancreas disease (PD) infection. Three specific freshwater diets were prepared: (i) A diet similar in composition to commercial salmon freshwater diets (Standard diet); (ii) A diet composed of vegetable oils (rapeseed, palm and linseed oils) mimicking the fat composition in aquatic insects – the natural diet of wild salmon in freshwater (Fatty acid diet); (iii) A diet enriched with possible immune modulating amino acids including dl -methionine, l -lysine, l -threonine and taurine (Amino acid diet). After seawater transfer, all fish were fed the same commercial diet. Head kidneys were extracted, and their leukocytes isolated from smolts right before transfer to seawater, from post smolts one and six weeks after transfer to seawater, and from post smolts in seawater after 8 weeks of ongoing PD infection. In addition, to provoke bacterial or virus induced inflammation in vitro, the individual leukocyte suspension from all fish were stimulated by lipopolysaccharide (LPS) or polyinosinic acid: polycytidylic acid (PIC). The transfer of smolts from fresh-to seawater changed the transcription of several types of genes. Particularly in isolates from fish fed the Standard or Fatty acid diet in freshwater, overall gene transcription (IL-1β , CD83 , INF-γ , cox2 , cd36 , MGAT2, catalase) declined. However, the Amino acid diet stimulated the LPS induced gene transcription of IL-1β , CD83 , Cox2 , and INF-γ at this stage. In freshwater smolts, PIC stimulated leukocytes showed higher transcription level of Mx and viperin in the Fatty acid and Amino acid diet groups compared to the Standard diet group. In seawater post smolts, Mx and viperin responded similarly to PIC challenge in all diet groups. Furthermore, leukocytes isolated from PD infected fish, continued responding to PIC, regardless of freshwater diet. • Modified Amino- and Fatty acid composition in freshwater diets can increase the immunological robustness of salmon parr towards virus infections during the freshwater phase. • The Amino acid composition in freshwater diets can be tailored to be protective against bacterial and oxidative damage in post smolts newly transferred to seawater. • When challenged with PIC, PD virus or PD virus + PIC, salmon immune cells use their energy to produce antiviral molecules, regardless of diet composition in freshwater. [ABSTRACT FROM AUTHOR]

The use of plant-based feeds warrants the supplementation with selenium (Se) to cover the requirement for Atlantic salmon. Depending on its chemical form, Se is a trace element with a narrow range between requirement and toxicity for most vertebrates. Information on safe upper limit for Atlantic salmon feed supplementation is lacking. Atlantic salmon (147 g) were fed a low natural background organic Se diet (0.45 mg Se kg −1 , wet weight (ww)) fortified with 5 graded levels of inorganic sodium selenite (0.45, 5.4, 11.0, 29.4, or 60.0 mg kg −1 ww) or organic selenomethionine (SeMet) (0.45, 6.2, 16.2, 21, or 39 mg kg −1 ww), in triplicate for 3 months. Excess Se supplementation was assessed by targeted biomarkers of Se toxicity pathways (e.g. markers of oxidative stress and lipid metabolism), as well as general adverse effect parameters (plasma biochemistry, hematology, liver histopathology, and growth). Safe limits were set by model-fitting the effect data in a dose-response (lower bound) bench mark dose (BMDL) evaluation. Fish fed the two highest selenite levels showed mortality while fish fed SeMet had no mortality. Fish fed 5.4–11 mg selenite kg −1 feed showed significantly (ANOVA, Tukey's t -test, p  < .05) increased liver oxidative stress, as seen from altered hepatic GSH and vitamin E levels, and liver damage as seen from increased plasma ALAT and liver histopathology such as degeneration and focal necrosis. Fish fed SeMet mainly showed liver pathology and kidney dysfunction as seen from altered plasma creatinine and total plasma proteins in fish fed ≥21 mg kg −1 , compared to control. For selenite exposed fish, a safe feed limit (BMDL) was set at 1–2 mg kg −1 ww feed (daily dose 0.01–0.02 mg kg BW −1  day −1 ), based on plasma ALAT increase, liver vitamin E depletion, and liver histopathology. For SeMet fed fish, the safe feed limit was higher than for selenite with a BMDL of 2.8 mg kg −1 ww (dose 0.03 mg kg BW −1  day −1 ), based on liver histopathology and plasma creatinine. In conclusion, with regards to fish health, Atlantic salmon seemed to tolerate the supplementation of selenite or SeMet to a level of total selenium of respectively 1–2 or 3 mg kg −1 feed, respectively, in a high plant-based salmon feed with background levels of 0.45 mg Se kg −1 . [ABSTRACT FROM AUTHOR]

Depending on its chemical form, selenium (Se) is a trace element with a narrow range between requirement and toxicity for most vertebrates. Traditional endpoints of Se toxicity include reduced growth, feed intake, and oxidative stress, while more recent finding describe disturbance in fatty acid synthesis as underlying toxic mechanism. To investigate overall metabolic mode of toxic action, with emphasis on lipid metabolism, a wide scope metabolomics pathway profiling was performed on Atlantic salmon ( Salmo salar ) (572 ± 7 g) that were fed organic and inorganic Se fortified diets. Atlantic salmon were fed a low natural background organic Se diet (0.35 mg Se kg −1 , wet weight (WW)) fortified with inorganic sodium selenite or organic selenomethionine-yeast (SeMet-yeast) at two levels (∼ 1–2 or 15 mg kg −1 , WW), in triplicate for 3 months. Apparent adverse effects were assessed by growth, feed intake, oxidative stress as production of thiobarbituric acid-reactive substances (TBARS) and levels of tocopherols, as well as an overall metabolomic pathway assessment. Fish fed 15 mg kg −1 selenite, but not 15 mg kg −1 SeMet-yeast, showed reduced feed intake, reduced growth, increased liver TBARS and reduced liver tocopherol. Main metabolic pathways significantly affected by 15 mg kg −1 selenite, and to a lesser extent 15 mg kg −1 SeMet-yeast, were lipid catabolism, endocannabinoids synthesis, and oxidant/glutathione metabolism. Disturbance in lipid metabolism was reflected by depressed levels of free fatty acids, monoacylglycerols and diacylglycerols as well as endocannabinoids. Specific for selenite was the significant reduction of metabolites in the S-Adenosylmethionine (SAM) pathway, indicating a use of methyl donors that could be allied with excess Se excretion. Dietary Se levels to respectively 1.1 and 2.1 mg kg −1 selenite and SeMet-yeast did not affect any of the above mentioned parameters. Apparent toxic mechanisms at higher Se levels (15 mg kg −1 ) included oxidative stress and altered lipid metabolism for both inorganic and organic Se, with higher toxicity for inorganic Se. [ABSTRACT FROM AUTHOR]

The extensive use of plant ingredients in novel aquafeeds have introduced mycotoxins to the farming of seafood. The emerging enniatin B (ENNB) and beauvericin (BEA) mycotoxins have been found in the novel aquafeeds and farmed fish. Little is known about the potential toxicity of ENNs and BEA in farmed fish and their feed-to-organ transfer. Atlantic salmon (Salmo salar) pre-smolt (75.3 ± 8.10 g) were fed four graded levels of spiked chemical pure ENNB or BEA feeds for three months, in triplicate tanks. Organismal adverse health end-point assessment included intestinal function (protein digestibility), disturbed hematology (red blood cell formation), bone formation (spinal deformity), overall energy use (feed utilization), and lipid oxidative status (vitamin E). Both dietary BEA and ENNB had a low (<∼0.01%) transfer to organs (kidney > liver > brain > muscle), with a higher transfer for ENNB compared to BEA. BEA caused a growth reduction combined with a decreased protein digestion and feed conversion rate- ENNB caused a stunted growth, unrelated to feed utilization capacity. In addition, ENNB caused anemia while BEA gave an oxidative stress response. Lower bench-mark dose regression assessment showed that high background levels of ENNB in commercial salmon feed could pose a risk for animal health, but not in the case of BEA. • Substitution of fish with plant ingredients increases mycotoxins in aquafeeds. • Dietary BEA causes growth reduction and feed conversion rate in salmon. • Dietary ENNB caused a stunted growth, unrelated to feed utilization capacity, and anemia in salmon. • Background levels of ENNB in salmon feed could form a risk to animal health. [ABSTRACT FROM AUTHOR]