Modulation of selenium tissue distribution and selenoprotein expression in Atlantic salmon ( Salmo salar L.) fed diets with graded levels of plant ingredients

Optimisation of trace mineral supplementation in diets for Atlantic salmon smolt with reference to holistic fish performance in terms of growth, health, welfare, and potential environmental impacts

The aquafeed ingredient inventory is ever changing, from marine to plant based, and recently evolving to incorporate increasing amounts of low trophic, side stream and circular economy based raw materials, each one contributing with variable amounts and qualities of macro- and micronutrients. Meeting the micronutrient requirement of farmed fish for healthy and efficient growth under normal and challenging conditions is of paramount importance. In this study we run a trial based on a 2 × 4 factorial design with three replications for each dietary treatment, where Atlantic salmon smolt were fed one of 8 experimental diets supplemented with either organic or inorganic mineral premixes (copper, iron, manganese, selenium, and zinc) at four dietary inclusion levels. We saw a trend for higher growth rate in the organic mineral groups irrespective of the dietary mineral levels. Mineral digestibility was negatively correlated with increasing mineral supplementation levels for all tested minerals but Se which increased with the increasing supplementation in the inorganic and up to the 2nd inclusion level in the organic mineral groups. Increasing mineral supplementation affected retention efficiency of Zn, Mn, Cu and Fe while mineral source affected only the retention of Se which was higher in the organic mineral groups. Moreover, fish obtained higher EPA and DHA in their body and increased slaughter yield in the organic as compared to the inorganic mineral groups and corroborated that trace mineral inclusion levels play a key role on salmon fillet's technical quality. More effects from different origin and dietary inclusion levels of trace minerals were seen on fillet yield, fillet technical and nutritional quality, bone strength, skin morphology, organ mineralization and midgut transcriptome.

Long-term feeding of Atlantic salmon with varying levels of dietary EPA + DHA alters the mineral status but does not affect the stress responses after mechanical delousing stress

Atlantic salmon were fed diets containing graded levels of EPA + DHA (1·0, 1·3, 1·6 and 3·5 % in the diet) and one diet with 1·3 % of EPA + DHA with reduced total fat content. Fish were reared in sea cages from about 275 g until harvest size (about 5 kg) and were subjected to delousing procedure (about 2·5 kg), with sampling pre-, 1 h and 24 h post-stress. Delousing stress affected plasma cortisol and hepatic mRNA expression of genes involved in oxidative stress and immune response, but with no dietary effects. Increasing EPA + DHA levels in the diet increased the trace mineral levels in plasma and liver during mechanical delousing stress period and whole body at harvest size. The liver Se, Zn, Fe, Cu, and Mn and plasma Se levels were increased in fish fed a diet high in EPA + DHA (3·5 %) upon delousing stress. Furthermore, increased dietary EPA + DHA caused a significant increase in mRNA expression of hepcidin antimicrobial peptide (HAMP), which is concurrent with downregulated transferrin receptor (TFR) expression levels. High dietary EPA + DHA also significantly increased the whole-body Zn, Se, and Mn levels at harvest size fish. Additionally, the plasma and whole-body Zn status increased, respectively, during stress and at harvest size in fish fed reduced-fat diet with less EPA + DHA. As the dietary upper limits of Zn and Se are legally added to the feeds and play important roles in maintaining fish health, knowledge on how the dietary fatty acid composition and lipid level affect body stores of these minerals is crucial for the aquaculture industry.

Selenium Nanoparticles Biosynthesized by Pantoea agglomerans and Their Effects on Cellular and Physiological Parameters in the Rainbow Trout Oncorhynchus mykiss

Simple Summary

Nanoparticles (Nps), new biotechnological tools, possess unique physical and chemical properties and are increasingly being used in several fields, such as manufacture, medicine and veterinary medicine. In this work, we evaluated the effects of selenium (Se) nanoparticles stabilized with L-Cysteine (Se⁰Nps/L-Cys) as a nutritional supplement, to modulate immunological, oxidative status, and productive parameters in O. mykiss. The results demonstrated that Se⁰Nps/L-Cys showed less toxicity and higher antioxidant activity than Se⁰Nps and Na₂SeO₃. The Se⁰Nps/L-Cys, as a dietary supplement, had a significantly better effect on both immunological and physiological parameters, causing improvements at the productive level of O. mykiss when compared with Se⁰Nps and Na₂SeO₃. We concluded that Se⁰Nps sythetised by P. agglomerans, used as dietary supplement, is an environmentally friendly and promising alternative for nutritional supplementation for O. mykiss.

Abstract

The applications of nanoparticles (Nps) as food additives, health enhancers, and antimicrobials in animal production are increasing. The aim of this study was to evaluate the effect of selenium (Se) nanoparticles (Se⁰Nps) stabilized with L-cysteine (Se⁰Nps/L-Cys), as a nutritional supplement, on immunological, oxidative status, and productive parameters in O. mykiss. TEM and SEM-EDS showed the accumulation of spherical Se⁰Nps entirely composed by elemental selenium (Se⁰) as intracellular and extracellular deposits in Pantoea agglomerans UC-32 strain. The in vitro antioxidant capacity of Se⁰Nps/L-Cys was significant more efficient ROS scavengers than Se⁰Nps and Na₂SeO₃. We also evaluate the effect of Se⁰Nps/L-Cys on cell viability and oxidative stress in RTgill-W1, RTS-11, or T-PHKM Oncorhynchus mykiss cell lines. Se⁰Nps/L-Cys showed less toxic and high antioxidant activity than Se⁰Nps and Na₂SeO₃. Finally, the dietary Se⁰Nps/L-Cys had a significant better effect on both plasma lysozyme and respiratory burst activity (innate immune response), on tissular Gpx activity (oxidative status), and on well-being (productive parameter) of O. mykiss when it is compared to Se⁰Nps and Na₂SeO₃. Se⁰Nps/L-Cys is a promising alternative for nutritional supplement for O. mykiss with better performance than Na₂SeO₃ and Se⁰Nps, ease to implementation, and reduced environmental impact.

Iodine Content of Wild and Farmed Seafood and Its Estimated Contribution to UK Dietary Iodine Intake

Iodine is an important nutrient for human health and development, with seafood widely acknowledged as a rich source. Demand from the increasing global population has resulted in the availability of a wider range of wild and farmed seafood. Increased aquaculture production, however, has resulted in changes to feed ingredients that affect the nutritional quality of the final product. The present study assessed the iodine contents of wild and farmed seafood available to UK consumers and evaluated its contribution to current dietary iodine intake. Ninety-five seafood types, encompassing marine and freshwater fish and shellfish, of wild and farmed origins, were purchased from UK retailers and analysed. Iodine contents ranged from 427.4 ± 316.1 to 3.0 ± 1.6 µg·100 g-1 flesh wet weight (mean ± SD) in haddock (Melanogrammus aeglefinus) and common carp (Cyprinus carpio), respectively, being in the order shellfish > marine fish > freshwater fish, with crustaceans, whitefish (Gadiformes) and bivalves contributing the greatest levels. Overall, wild fish tended to exhibit higher iodine concentrations than farmed fish, with the exception of non-fed aquaculture species (bivalves). However, no significant differences were observed between wild and farmed Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), and turbot (Psetta maxima). In contrast, farmed European seabass (Dicentrarchus labrax) and seabream (Sparus aurata) presented lower, and Atlantic halibut (Hippoglossus hippoglossus) higher, iodine levels than their wild counterparts, most likely due to the type and inclusion level of feed ingredients used. By following UK dietary guidelines for fish consumption, a portion of the highest oily (Atlantic mackerel, Scomber scombrus) and lean (haddock) fish species would provide two-thirds of the weekly recommended iodine intake (980 µg). In contrast, actual iodine intake from seafood consumption is estimated at only 9.4-18.0% of the UK reference nutrient intake (140 µg·day-1) across different age groups and genders, with females obtaining less than their male equivalents.

Nutrition and Metabolism of Minerals in Fish

Simple Summary

Our aim is to introduce the mineral nutrition of fish and explain the complexity of determining requirements for these elements, which are absorbed and excreted by the fish into the surrounding water. To date, only the requirements for nine minerals have been investigated. The review is focused on the absorption and the dietary factors that reduce their absorption from feed ingredients of plant and animal origin. Some diseases, such as cataracts, anemia and bone deformity, have been linked to dietary deficiency of minerals.

Abstract

Aquatic animals have unique physiological mechanisms to absorb and retain minerals from their diets and water. Research and development in the area of mineral nutrition of farmed fish and crustaceans have been relatively slow and major gaps exist in the knowledge of trace element requirements, physiological functions and bioavailability from feed ingredients. Quantitative dietary requirements have been reported for three macroelements (calcium, phosphorus and magnesium) and six trace minerals (zinc, iron, copper, manganese, iodine and selenium) for selected fish species. Mineral deficiency signs in fish include reduced bone mineralization, anorexia, lens cataracts (zinc), skeletal deformities (phosphorus, magnesium, zinc), fin erosion (copper, zinc), nephrocalcinosis (magnesium deficiency, selenium toxicity), thyroid hyperplasia (iodine), muscular dystrophy (selenium) and hypochromic microcytic anemia (iron). An excessive intake of minerals from either diet or gill uptake causes toxicity and therefore a fine balance between mineral deficiency and toxicity is vital for aquatic organisms to maintain their homeostasis, either through increased absorption or excretion. Release of minerals from uneaten or undigested feed and from urinary excretion can cause eutrophication of natural waters, which requires additional consideration in feed formulation. The current knowledge in mineral nutrition of fish is briefly reviewed.

Processing Mixed Mesopelagic Biomass from the North-East Atlantic into Aquafeed Resources; Implication for Food Safety

Aquaculture produces most of the world's seafood and is a valuable food source for an increasing global population. Low trophic mesopelagic biomasses have the potential to sustainably supplement aquafeed demands for increased seafood production. The present study is a theoretical whole-chain feed and food safety assessment on ingredients from mesopelagic biomass and the resulting farmed fish fed these ingredients, based on analysis of processed mesopelagic biomass. Earlier theoretical estimations have indicated that several undesirable compounds (e.g., dioxins and metals and fluoride) would exceed the legal maximum levels for feed and food safety. Our measurements on processed mesopelagic biomasses show that only fluoride exceeds legal feed safety limits. Due to high levels of fluoride in crustaceans, their catch proportion will dictate the fluoride level in the whole biomass and can be highly variable. Processing factors are established that can be used to estimate the levels of undesirables in mesopelagic aquafeed ingredients from highly variable species biomass catches. Levels of most the studied undesirables (dioxins, PCBs, organochlorine pesticides, brominated flame retardant, metals, metalloids) were generally low compared to aquafeed ingredients based on pelagic fish. Using a feed-to-fillet aquaculture transfer model, the use of mesopelagic processed aquafeed ingredients was estimated to reduce the level of dioxins and PCBs by ~30% in farmed seafood such as Atlantic salmon.

Long-term effect of parental selenium supplementation on the one-carbon metabolism in rainbow trout (Oncorhynchus mykiss) fry exposed to hypoxic stress

This study evaluated how different forms of selenium (Se) supplementation into rainbow trout broodstock diets modified the one-carbon metabolism of the progeny after the beginning of exogenous feeding and followed by hypoxia challenge. The progeny of three groups of rainbow trout broodstock fed either a control diet (Se level: 0·3 µg/g) or a diet supplemented with inorganic sodium selenite (Se level: 0·6 µg/g) or organic hydroxy-selenomethionine (Se level: 0·6 µg/g) was cross-fed with diets of similar Se composition for 11 weeks. Offspring were sampled either before or after being subjected to an acute hypoxic stress (1·7 mg/l dissolved oxygen) for 30 min. In normoxic fry, parental Se supplementation allowed higher glutathione levels compared with fry originating from parents fed the control diet. Parental hydroxy-selenomethionine treatment also increased cysteine and cysteinyl-glycine concentrations in fry. Dietary Se supplementation decreased glutamate-cysteine ligase (cgl) mRNA levels. Hydroxy-selenomethionine feeding also lowered the levels of some essential free amino acids in muscle tissue. Supplementation of organic Se to parents and fry reduced betaine-homocysteine S-methyltransferase (bhmt) expression in fry. The hypoxic stress decreased whole-body homocysteine, cysteine, cysteinyl-glycine and glutathione levels. Together with the higher mRNA levels of cystathionine beta-synthase (cbs), a transsulphuration enzyme, this suggests that under hypoxia, glutathione synthesis through transsulphuration might have been impaired by depletion of a glutathione precursor. In stressed fry, S-adenosylmethionine levels were significantly decreased, but S-adenosylhomocysteine remained stable. Decreased bhmt and adenosylmethionine decarboxylase 1a (amd1a) mRNA levels in stressed fry suggest a nutritional programming by parental Se also on methionine metabolism of rainbow trout.

The nutritional and cardiovascular health benefits of rapeseed oil-fed farmed salmon in humans are not decreased compared with those of traditionally farmed salmon: a randomized controlled trial

PURPOSE

Farmed fish are increasingly raised on feeds containing vegetable oils, which affects their composition and possibly health properties. We investigated the effects of consuming farmed salmon, raised on different feeding regimes, on nutrient status and health outcomes in healthy subjects.

METHODS

Salmon were grown on feeds containing mainly fish oil (FO) or rapeseed oil (RO), resulting in an eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) content of fillets of 2.1 or 0.9 g/100 g, respectively. In a randomized parallel controlled trial, 51 healthy subjects were allocated to consume 2 portions/week of FO salmon (n = 17), RO salmon (n = 17) or no additional salmon (Control, n = 17) as part of their habitual diet, for 18 weeks. We collected blood at 0, 9 and 18 weeks to measure omega-3 index (O3I) in red blood cells, plasma markers of cardiovascular risk, serum 25(OH)-vitamin D₃ (25(OH)D₃) and plasma trace elements.

RESULTS

After 18 weeks, O3I was similarly increased in subjects consuming 2 portions/week of FO or RO salmon compared to control (both p < 0.05). Serum 25(OH)D₃ was significantly higher, whereas plasma triacylglycerols were significantly lower in subjects consuming RO salmon compared to control (both p < 0.05). Heart rate was significantly lower in subjects consuming FO salmon after 9 weeks, compared to control (p < 0.01). Salmon consumption did not affect other markers.

CONCLUSION

Consuming two portions/week of salmon raised on rapeseed oil rather than fish oil increased the O3I and vitamin D status, and decreased plasma triacylglycerols. These outcomes endorse opportunities for developing more sustainable feeds within aquaculture food systems.

CLINICAL TRIAL REGISTRY

This trial was registered at clinicaltrials.gov as NCT01916434.

Comparison of intracellular trace element distributions in the liver and gills of the invasive freshwater fish species, Prussian carp (Carassius gibelio Bloch, 1782)

Prussian carp (Carassius gibelio) is an invasive freshwater fish known for its high tolerance to aquatic pollution. Our aim was to try to clarify its tolerance to increased exposure to metals/nonmetals, by determining their cytosolic distributions among peptides/proteins of different molecular masses (MM), which form a part of the fish protective mechanisms. The applied approach consisted of fractionation of gill and hepatic cytosols of Prussian carp from the Croatian river Ilova by size-exclusion high performance liquid chromatography, whereas Cd, Cu, Zn, Fe, Mo, and Se analyses were done by high resolution inductively coupled plasma mass spectrometry. The results indicated high detoxification of Cd by its binding to metallothioneins (MTs) in both fish organs. In addition, binding to MTs was observed for Cu in both organs and for Zn in the liver, whereas clear Zn binding to MTs in the gills was not recorded. Zinc in the gills was predominantly bound to proteins of higher MM (50-250 kDa) and to biomolecules of MM below 2 kDa. Predominant Fe binding to proteins of MM of ~400 kDa (presumably storage protein ferritin) was observed in the liver, whereas in the gills Fe was mainly associated to proteins of MM of ~15-65 kDa (presumably hemoglobin oligomers). Maximum Mo and Se elutions in the liver were noted at 235 kDa and 141 kDa, respectively, and in the gills below 10 kDa. The striking difference was observed between two organs of Prussian carp, with predominant metal/nonmetal binding to high MM proteins (e.g., enzymes, storage proteins) in the liver, and to very low MM biomolecules (<10 kDa) in the gills (e.g., antioxidants, metallochaperones, nonprotein cofactors). Such metal/nonmetal distributions within the gills, as the first site of defense, as well as association of several metals to MTs, indicated highly developed defense mechanisms in some organs of Prussian carp.

Feed-to-Fillet Transfer of Selenite and Selenomethionine Additives to Plant-Based Feeds to Farmed Atlantic Salmon Fillet

This study investigated the transfer kinetics of dietary selenite and selenomethionine (SeMet) to the fillet of farmed Atlantic salmon (Salmo salar). The uptake and elimination rate constants of the two selenium (Se) forms were determined in Atlantic salmon fed either selenite- or SeMet-supplemented diets followed by a depuration period. The fillet half-life of selenite and SeMet was 779 ± 188 and 339 ± 103 days, respectively. The elimination and uptake rates were used in a simple one-compartmental kinetic model to predict levels in fillet based on long-term (whole production cycle) feeding with given dietary Se levels. Model predictions for Atlantic salmon fed plant-based feeds low in natural Se and supplemented with either 0.2 mg of selenite or SeMet kg^-1 gave a predicted fillet level of 0.042 and 0.058 mg Se kg^-1 wet weight, respectively. Based on these predictions and the European Food Safety Authority risk assessment of Se feed supplementation for food-producing terrestrial farm animals, the supplementation with 0.2 mg of selenite kg^-1 would likely be safe for the most sensitive group of consumers (toddlers). However, supplementing feed to farm animals, including salmon, with 0.2 mg of SeMet kg^-1 would give a higher (114%) Se intake than the safe upper intake limit for toddlers.

Selenium and selenium species in feeds and muscle tissue of Atlantic salmon

Selenium (Se) is an essential element for animals, including fish. Due to changes in feed composition for Atlantic salmon (Salmo salar), it may be necessary to supplement feeds with Se. In the present work, the transfer of Se and Se species from feed to muscle of Atlantic salmon fed Se supplemented diets was studied. Salmon were fed basal fish feed (0.35 mg Se/kg and 0.89 mg Se/kg feed), or feed supplemented either with selenised yeast or sodium selenite, at low (1-2 mg Se/kg feed) and high (15 mg Se/kg feed) levels, for 12 weeks. For the extraction of Se species from fish muscle, enzymatic cleavage with protease type XIV was applied. The extraction methods for Se species from fish feed were optimised, and two separate extraction procedures were applied, 1) enzymatic cleavage for organic Se supplemented feeds and 2) weak alkaline solvent for inorganic Se supplemented feeds, respectively. For selenium speciation analysis in feed and muscle tissue anion-exchange HPLC-ICP-MS for analysis of inorganic Se species and cation-exchange HPLC-ICP-MS for analysis of organic Se species, were applied. In addition, reversed phase HPLC-ICP-MS was applied for analysis of selenocysteine (SeCys) in selected muscle samples. The results demonstrated that supplemented Se (organic and inorganic) accumulated in muscle of Atlantic salmon, and a higher retention of Se was seen in the muscle of salmon fed organic Se diets. Selenomethionine (SeMet) was the major Se species in salmon fed basal diets and diets supplemented with organic Se, accounting for 91-118% of the total Se. In contrast, for muscle of salmon fed high inorganic Se diet, SeMet accounted for 30% of the total Se peaks detected. Several unidentified Se peaks were detected, in the fish fed high inorganic diet, and analysis showed indicated SeCys is a minor Se species present in this fish muscle tissue.

The potential impact of compositional changes in farmed fish on its health-giving properties: is it time to reconsider current dietary recommendations?

Assessment of national dietary guidelines in a number of European countries reveals that some are based on cohort studies, focusing on total seafood consumption, while others are based on the content of EPA and DHA, distinguishing between oily and other fish. The mean actual intake of fish in most countries is around or below the recommended intake, with differences in intake of fish being present between sex and age groups. Many people do not reach the national recommendation for total fish intake. Dietary recommendations for fish and EPA/DHA are based mainly on data collected more than 10 years ago. However, methods of farmed fish production have changed considerably since then. The actual content of EPA and DHA in farmed salmon has nearly halved as the traditional finite marine ingredients fish meal and fish oil in salmon diets have been replaced with sustainable alternatives of terrestrial origin. As farmed salmon is an important source of EPA and DHA in many Western countries, our intake of these fatty acids is likely to have decreased. In addition, levels of vitamin D and Se are also found to have declined in farmed fish in the past decade. Significant changes in the EPA and DHA, vitamin D and Se content of farmed fish means that average intakes of these nutrients in Western populations are probably lower than before. This may have consequences for the health-giving properties of fish as well as future dietary recommendations for fish intake.