Impact of selenium supplementation on fish antiviral responses: a whole transcriptomic analysis in rainbow trout (Oncorhynchus mykiss) fed supranutritional levels of Sel-Plex®

The effect of selenium on the intestinal health of juvenile grass carp based on the ERS-autophagy pathway

Selenium (Se), a trace element, is vital for the maintenance of cellular redox balance, thyroid hormone metabolism, inflammation, and immunity. Aeromonas hydrophila (A. hydrophila) is a common Gram-negative conditional pathogenic bacterium in fish culture, posing a serious threat to intensive aquaculture. Our study investigated the influence of dietary Se on the intestinal immune function of grass carp (Ctenopharyngodon idella) and the related regulatory mechanisms. The 2160 healthy juvenile grass carp (9.76 ± 0.005 g) were randomly assigned to 6 test groups of 6 replicates each, and fed graded selenomethionine (0.05, 0.20, 0.40, 0.61, 0.77, 0.98 mg Se/kg diet) for 70 days and then injected with A. hydrophila for a 6-day attack test. The results indicated that appropriate Se levels (0.40 mg/kg diet) alleviated intestinal damage caused by A. hydrophila and increased intestinal immune substances C3 and C4 levels as well as the activity of acid phosphatase (ACP) and lysozyme (LZ) (P > 0.05). Appropriate levels of Se (0.40 mg/kg-0.61 mg/kg diet) decreased intestinal pro-inflammatory cytokines (IFN-γ2, IL-6, IL-12p35, IL-17 A F and IL-17D) mRNA levels (P > 0.05) and increased intestinal anti-inflammatory factors (TGF-β1, IL-4/13A, IL-4/13B, IL-10 and IL-22) mRNA levels (P > 0.05) in juvenile grass carp. Further studies revealed that Se (0.40 mg/kg-0.61 mg/kg diet) inhibited intestinal endoplasmic reticulum stress (ERS)-related signaling pathway. Furthermore, we found that appropriate levels of Se (0.40 mg/kg-0.61 mg/kg diet) inhibited intestinal autophagy in juvenile grass carp, which may be related to ULK1, Beclin 1, ATG5, ATG12, LC3, and P62. In conclusion, appropriate levels of Se can alleviate intestinal inflammation and inhibit ERS and autophagy in juvenile grass carp. A quadratic regression analysis of intestinal ACP and LZ also indicated that the Se requirements of juvenile grass carp were 0.59 and 0.51 mg/kg, respectively.

Acclimation to higher temperature and antioxidant supplemented diets improved rainbow trout (Oncorhynchus mykiss) resilience to heatwaves

Coldwater species are challenged with increasing water temperatures and fluctuations over their upper thermal limits. This study evaluated the potential of acclimation to higher temperature and dietary antioxidants capacity to mitigate the adverse effects of heat shocks in rainbow trout. To this end, rainbow trout fingerlings were acclimated at optimal (14 °C) and high (20 °C) temperatures and fed on selenium (5 mg/kg) and polyphenol (2 g/kg) supplemented diets for 60 days and then were exposed to heat shocks by increasing water temperature up to 30 °C. Growth performance, survival rate, haemato-immunological parameters, and expression of HSP70α, HSP70β, HSP90β, and IL-1β genes were measured to evaluate the hypothesises. The rainbow trout acclimated to 20 °C and fed on antioxidants supplemented diets showed a significantly higher aftershock survival rate. Moreover, fish acclimated to higher temperature showed higher red blood cell counts as well as serum total protein and albumin during the acclimation trial and heat shocks phase. Acclimation to higher temperature and feeding on antioxidants remarkably enhanced fish immune and antioxidant capacity in comparison to fish adapted to cold water and fed on the basal diet measured by improved respiratory burst and lysozyme activities and upregulation of IL-1β expression during exposure of fish to heat shocks. Furthermore, fish acclimated to higher temperature, especially those fed on antioxidant supplemented diets, showed lower expression levels of HSPs genes during the heat shock phase, indicating that high heat shocks were less stressful for these fish in comparison to cold water acclimated fish. This finding was also supported by lower cortisol levels during heat shocks in fish acclimated to higher temperature. In conclusion, the results of this study indicated that acclimation to higher temperature and/or fed on diets supplemented by selenium and polyphenol, can help to mitigate the adverse effects of the heat shock in rainbow trout.

Differential tissue immune stimulation through immersion in bacterial and viral agonists in the Antarctic Notothenia rossii

The genome evolution of Antarctic notothenioids has been modulated by their extreme environment over millennia and more recently by human-caused constraints such as overfishing and climate change. Here we investigated the characteristics of the immune system in Notothenia rossii and how it responds to 8 h immersion in viral (Poly I:C, polyinosinic: polycytidylic acid) and bacterial (LPS, lipopolysaccharide) proxies. Blood plasma antiprotease activity and haematocrit were reduced in Poly I:C-treated fish only, while plasma protein, lysozyme activity and cortisol were unchanged with both treatments. The skin and duodenum transcriptomes responded strongly to the treatments, unlike the liver and spleen which had a mild response. Furthermore, the skin transcriptome responded most to the bacterial proxy (cell adhesion, metabolism and immune response processes) and the duodenum (metabolism, response to stress, regulation of intracellular signal transduction, and immune system responses) to the viral proxy. The differential tissue response to the two proxy challenges is indicative of immune specialisation of the duodenum and the skin towards pathogens. NOD-like and C-type lectin receptors may be central in recognising LPS and Poly I:C. Other antimicrobial compounds such as iron and selenium-related genes are essential defence mechanisms to protect the host from sepsis. In conclusion, our study revealed a specific response of two immune barrier tissue, the skin and duodenum, in Notothenia rossii when exposed to pathogen proxies by immersion, and this may represent an adaptation to pathogen infective strategies.

Selenium nanoparticles: Enhanced nutrition and beyond

Selenium is a trace nutrient that has both nutritional and nutraceutical functions, whereas narrow nutritional range of selenium intake limits its use. Selenium nanoparticles (SeNPs) are less toxic and more bioavailable than traditional forms of selenium, suggesting that SeNPs have the potential to replace traditional selenium in food industries and/or biomedical fields. From the perspective of how SeNPs can be applied in health area, this review comprehensively discusses SeNPs in terms of its preparation, nutritional aspect, detoxification effect of heavy metals, nutraceutical functions and anti-pathogenic microorganism effects. By physical, chemical, or biological methods, inorganic selenium can be transformed into SeNPs which have increased stability and bioavailability as well as low toxicity. SeNPs are more effective than traditional selenium form in synthesizing selenoproteins like glutathione peroxidases. SeNPs can reshape the digestive system to facilitate digestion and absorption of nutrients. SeNPs have shown excellent potential to adjunctively treat cancer patients, enhance immune system, control diabetes, and prevent rheumatoid arthritis. Additionally, SeNPs have good microbial anti-pathogenic effects and can be used with other antimicrobial agents to fight against pathogenic bacteria, fungi, or viruses. Development of novel SeNPs with enhanced functions can greatly benefit the food-, nutraceutical-, and biomedical industries.

Effect of Dietary Selenium on the Growth and Immune Systems of Fish

Dietary selenium (Se) is an essential component that supports fish growth and the immune system. This review attempts to provide insight into the biological impacts of dietary Se, including immunological responses, infection defense, and fish species growth, and it also identifies the routes via which it enters the aquatic environment. Dietary Se is important in fish feed due to its additive, antioxidant, and enzyme properties, which aid in various biological processes. However, excessive intake of it may harm aquatic ecosystems and potentially disrupt the food chain. This review explores the diverse natures of dietary Se, their impact on fish species, and the biological methods for eliminating excesses in aquatic environments. Soil has a potential role in the distribution of Se through erosion from agricultural, industrial, and mine sites. The research on dietary Se's effects on fish immune system and growth can provide knowledge regarding fish health, fish farming strategies, and the health of aquatic ecosystems, promoting the feed industry and sustainable aquaculture. This review provides data and references from various research studies on managing Se levels in aquatic ecosystems, promoting fish conservation, and utilizing Se in farmed fish diets.

Selenium nanoparticles improve fish sperm quality by enhancing glucose uptake capacity via AMPK activation

Appropriate additives can provide a suitable physiological environment for storage of fish sperm and facilitate the large-scale breeding of endangered species and commercial fish. Suitable additives for fish sperm storage in vitro are required for artificial insemination. This study evaluate the effects of 0.1, 0.5, 1.5, and 4.5 mg/L selenium nanoparticles (SeNPs) on the quality of Schizothorax prenanti and Onychostoma macrolepis sperm storage in vitro at 4 °C for 72 h. We found that 0.5 mg/L SeNPs was a suitable concentration for maintaining the normal physiological state of O. macrolepis sperm during storage at 4 °C (p < 0.05). Higher adenosine triphosphate (ATP) content of O. macrolepis sperm before and after activation was present at that concentration. To further explore the potential mechanism of action of SeNPs on O. macrolepis sperm, western blotting and glucose uptake analyses were performed. The results implied that after 24 h of in vitro preservation, 0.5 mg/L SeNPs significantly improved p-AMPK levels and glucose uptake capacity of O. macrolepis sperm, while compound C (CC), the inhibitor of activated AMP-activated protein kinase (p-AMPK), significantly restricted the function of SeNPs on stored sperm. Similar effects of 0.5 mg/L SeNPs were found on Schizothorax prenanti sperm. Our study demonstrates that SeNPs maintained ATP content and O. macrolepis and Schizothorax prenanti sperm function during storage in vitro for 72 h, possibly because SeNPs enhanced the glucose uptake capacity of sperm by maintaining the level of p-AMPK.

Metabolomics and Proteomics Responses of Largemouth Bass (Micropterus salmoides) Muscle under Organic Selenium Temporary Rearing

Organic selenium has been widely studied as a nutritional supplement for animal feed. However, there are few studies on the effect of organic selenium on flesh quality. In this study, the effects of organic selenium (yeast selenium (YS), Se 0.002 mg/L) on the metabolism and protein expression in Micropterus salmoides muscle under temporary fasting condition (6 weeks) were investigated. The muscle structure was observed through a microscope, and regulatory pathways were analyzed using proteomics and metabolomics methods. Electron microscopy showed that YS made the muscle fibers of M. salmoides more closely aligned. Differential analysis identified 523 lipid molecules and 268 proteins. The numbers of upregulated and downregulated proteins were 178 and 90, respectively, including metabolism (46.15%), cytoskeleton (11.24%) and immune oxidative stress (9.47%), etc. Integrated analyses revealed that YS enhanced muscle glycolysis, the tricarboxylic acid cycle and oxidative phosphorylation metabolism. In the YS group, the content of eicosapentaenoic acid was increased, and that of docosahexaenoic acid was decreased. YS slowed down protein degradation by downregulating ubiquitin and ubiquitin ligase expression. These results suggest that organic selenium can improve M. salmoides muscle quality through the aforementioned pathways, which provides potential insights into the improvement of the quality of aquatic products, especially fish.

Lost and Found: The Family of NF-κB Inhibitors Is Larger than Assumed in Salmonid Fish

NF-κB signalling is largely controlled by the family of 'inhibitors of NF-κB' (IκB). The relevant databases indicate that the genome of rainbow trout contains multiple gene copies coding for iκbα (nfkbia), iκbε (nfkbie), iκbδ (nkfbid), iκbζ (nfkbiz), and bcl3, but it lacks iκbβ (nfkbib) and iκbη (ankrd42). Strikingly, three nfkbia paralogs are apparently present in salmonid fish, two of which share a high sequence identity, while the third putative nfkbia gene is significantly less like its two paralogs. This particular nfkbia gene product, iκbα, clusters with the human IκBβ in a phylogenetic analysis, while the other two iκbα proteins from trout associate with their human IκBα counterpart. The transcript concentrations were significantly higher for the structurally more closely related nfkbia paralogs than for the structurally less similar paralog, suggesting that iκbβ probably has not been lost from the salmonid genomes but has been incorrectly designated as iκbα. In the present study, two gene variants coding for iκbα (nfkbia) and iκbε (nfkbie) were prominently expressed in the immune tissues and, particularly, in a cell fraction enriched with granulocytes, monocytes/macrophages, and dendritic cells from the head kidney of rainbow trout. Stimulation of salmonid CHSE-214 cells with zymosan significantly upregulated the iκbα-encoding gene while elevating the copy numbers of the inflammatory markers interleukin-1-beta and interleukin-8. Overexpression of iκbα and iκbε in CHSE-214 cells dose-dependently quenched both the basal and stimulated activity of an NF-κB promoter suggesting their involvement in immune-regulatory processes. This study provides the first functional data on iκbε-versus the well-researched iκbα factor-in a non-mammalian model species.

Voyage of selenium from environment to life: Beneficial or toxic?

Selenium (Se), a naturally occurring metalloid, is an essential micronutrient for life as it is incorporated as selenocysteine in proteins. Although beneficial at low doses, Se is hazardous at high concentrations and poses a serious threat to various ecosystems. Due to this contrasting 'dual' nature, Se has garnered the attention of researchers wishing to unravel its puzzling properties. In this review, we describe the impact of selenium's journey from environment to diverse biological systems, with an emphasis on its chemical advantage. We describe the uneven distribution of Se and how this affects the bioavailability of this element, which, in turn, profoundly affects the habitat of a region. Once taken up, the subsequent incorporation of Se into proteins as selenocysteine and its antioxidant functions are detailed here. The causes of improved protein function due to the incorporation of redox-active Se atom (instead of S) are examined. Subsequently, the reasons for the deleterious effects of Se, which depend on its chemical form (organo-selenium or the inorganic forms) in different organisms are elaborated. Although Se is vital for the function of many antioxidant enzymes, how the pro-oxidant nature of Se can be potentially exploited in different therapies is highlighted. Furthermore, we succinctly explain how the presence of Se in biological systems offsets the toxic effects of heavy metal mercury. Finally, the different avenues of research that are fundamental to expand our understanding of selenium biology are suggested.

Effect of an Established Nutritional Level of Selenium on Energy Metabolism and Gene Expression in the Liver of Rainbow Trout

The nutritional selenium (Se) has been demonstrated to have health-boosting effects on fish. However, its effect on fish energy metabolism remains unclear. This study explores the effect and underlying mechanism of the action of nutritional Se on energy metabolism in fish. Rainbow trout (Oncorhynchus mykiss) were fed a basal diet (0 mg Se/kg diet) and a diet containing an already established nutritional Se level (2 mg Se/kg diet, based on Se-yeast) for 30 days. After the feeding experiment, the plasma and liver biochemical profiles and liver transcriptome were analyzed. The results showed that the present nutritional level of Se significantly increased liver triglyceride, total cholesterol, and plasma total cholesterol contents (P < 0.05) compared with the control. Transcriptome analysis showed that 336 and 219 genes were significantly upregulated and downregulated, respectively. Gene enrichment analysis showed that many differentially expressed genes (DEGs) were associated with lipid metabolism pathways (fatty acid biosynthesis, fatty acid elongation, and unsaturated fatty acid biosynthesis), carbohydrate metabolism pathways (glycolysis, the pentose phosphate pathway, and the citrate cycle), and the oxidative phosphorylation pathway. Real-time quantitative PCR (Q-PCR) validation results showed that the expression profiles of 15 genes exhibited similar trends both in RNA sequencing (RNA-seq) and Q-PCR analysis. These results reveal that optimum dietary Se activates glucose catabolic processes, fatty acid biosynthetic processes, and energy production and hence produces higher liver lipid content. This study concludes that the previously established level of nutritional Se (Se-yeast) (2 mg/kg diet, fed basis) for rainbow trout promotes energy storage in the liver, which may benefit fish growth to some extent.

The dietary supplementation of zinc oxide and selenium nanoparticles enhance the immune response in freshwater fish Oreochromis mossambicus against aquatic pathogen Aeromonas hydrophila

BACKGROUND

Green nanoparticles are subjected as an immunostimulant against bacterial pathogens.

METHODS

Murraya koenigii berry extract-based synthesized zinc oxide nanoparticles (Mb-ZnO NPs) and selenium nanoparticles (Mb-Se NPs) were relatively analyzed for immunostimulation in serum and mucus fish Oreochromis mossambicus against Aeromonas hydrophila infections. Initial minimum inhibitory concentration (MIC) was determined for both Mb-ZnO NPs and Mb-Se NPs followed by specific growth rate (SGR), antioxidant level (Superoxide dismutase activity (SOD), Catalase activity (CA), and Glutathione peroxidase activity (GPx)), and immune parameters Myeloperoxidase activity (MPO), Respiratory burst activity (RBA), Lysozyme activity (LYZ), Alkaline phosphatase activity (ALP), Serum antiprotease activity and Natural complement activity (NAC).

RESULTS

The potential bacterial inhibition property of Mb-ZnO NPs and Mb-Se NPs exhibited the most negligible concentration of 25 and 15 μg mL^-1, respectively, against A. hydrophila. In addition, Mb-ZnO NPs and Mb-Se NPs exhibited 70-80 % and 90-95 % diminished biofilm activity at 50 μg mL^-1 that was viewed under an inverted research microscope and confocal laser scanning microscopy (CLSM). Protein leakage and nucleic acid leakage assay quantified oozed out protein and nucleic acid from A. hydrophila that confirms Mb-Se NPs exhibited vigorous antibacterial activity than Mb-ZnO NPs at tested concentrations. Oreochromis mossambicus fed with Mb-ZnO NPs and Mb-Se NPs supplemented diet at different concentrations (0.5 mg/kg, 1 mg/kg and 2 mg/kg) improved SGR along with a rise in the immune response of those fishes against A. hydrophila infection. Serum and mucus of fish fed with Mb-Se NPs supplemented diet exhibited a significant rise in antioxidant level SOD, CA and GPx at a dosage of 2 mg/kg. Likewise, lipid peroxidation assay detected significantly diminished oxidative stress in the serum and mucus of fish fed with Mb-Se NPs supplemented diet (2 mg/kg). Enhanced immune parameters in serum and mucus of fish fed with Mb-Se NPs supplemented diet determined by MPO, RBA, LYZ, ALP, Serum antiprotease activity and NAC.

CONCLUSION

Thus O. mossambicus fed with Mb-Se NPs supplemented diet was less prone to become infected by aquatic pathogen A. hydrophila established by challenge study. On the whole, Mb-Se NPs supplemented diet ensured the rise in antioxidant response that boosts the immune responses and reduces the chance of getting infected against A. hydrophila infections.

Organic Selenium (OH-MetSe) Effect on Whole Body Fatty Acids and Mx Gene Expression against Viral Infection in Gilthead Seabream (Sparus aurata) Juveniles

The supplementation of fish diets with OH-SeMet reduces oxidative stress and modulates immune response against bacterial infection. However, despite the importance of essential polyunsaturated fatty acids in fish nutrition and their high risk of oxidation, the potential protective effect of OH-SeMet on these essential fatty acids has not been studied in detail. Moreover, while viral infection is very relevant in seabream production, no studies have focused the Se effects against viral infection. The aim of the present study was to assess the impact of dietary supplementation with OH-SeMet on gilthead seabream fatty acid profiles, growth performance and response against viral infection. Gilthead seabream juveniles (21.73 ± 0.27 g) were fed for 91 days with three experimental diets, a control diet without supplementation of Se (0.29 mg Se kg diet-1) and two diets supplemented with OH-SeMet (0.52 and 0.79 mg Se kg diet-1). A crowding stress test was performed at week 7 and an anti-viral response challenge were conducted at the end of the feeding trial. Selenium, proximate and fatty acid composition of diets and body tissues were analyzed. Although fish growth was not affected, elevation in dietary Se proportionally raised Se content in body tissues, increased lipid content in the whole body and promoted retention and synthesis of n-3 polyunsaturated fatty acids. Specifically, a net production of DHA was observed in those fish fed diets with a higher Se content. Additionally, both monounsaturated and saturated fatty acids were significantly reduced by the increase in dietary Se. Despite the elevation of dietary Se to 0.79 mg kg-1 not affecting basal cortisol levels, 2 h post-stress plasma cortisol levels were markedly increased. Finally, at 24 h post-stimulation, dietary OH-SeMet supplementation significantly increased the expression of the antiviral response myxovirus protein gene, showing, for the first time in gilthead seabream, the importance of dietary Se levels on antiviral defense.

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.

Trial for use nanoselenium particle with different dietary regime in Oreochromis niloticus and Mugil cephalus polyculture ponds: Growth efficiency, haematological, antioxidant, immunity and transcriptional analysis

Background

Fish farming is one of the most productive economies in the world. One of the essential goals in fish production is to minimize processing costs while maintaining and increasing the vital functions, weight and immunity of fish.

Objective

We conducted this study to explore nanoselenium (Nano‐Se) particles in various feeding schemes.

Material and Method

Nano‐Se particles incorporated in the basal diet at (0.5 mg/kg diet), and the fish was divided into six groups after adaptation as the follows: The first group was feed daily with a diet containing Nano‐Se (0.5 mg/kg diet); the second group was exposed to a feeding programme in which it has day feeding followed by day of starvation with a diet containing Nano‐Se (0.5 mg/kg diet); the third group was day feeding followed by 2 days of starvation; the fourth group served as a negative control group in which this group was continuous feeding with a basal diet without Nano‐Se; the fifth group was day feeding with the basal diet followed by a day of starvation; and the sixth group was day feeding with basal diet followed by 2 days of starvation.

Result

Our result revealed that Group 2 showed significant improvement in haematological parameters, red blood cells and haemoglobin with a substantial increase in total protein (p < 0.05) as well as lysosomal and phagocytic activity with considerable upregulation of growth hormone and insulin growth factor 1 in addition to markedly increase in the pro‐inflammatory cytokines. Finally, this study offers the first‐time dietary regime with Nano‐Se supplementation that saves the feeding cost and increases fish welfare and growth.

Increased dietary availability of selenium in rainbow trout (Oncorhynchus mykiss) improves its plasma antioxidant capacity and resistance to infection with Piscirickettsia salmonis

Salmonid Rickettsial Septicaemia (SRS), caused by Piscirickettsia salmonis, is the most important infectious disease in the Chilean salmon farming industry. An opportunity to control this disease is to use functional micronutrients to modulate host mechanisms of response to the infection. Since P. salmonis may affect the host antioxidant system in salmonids, particularly that dependent on selenium (Se), we hypothesized that fish’s dietary selenium supplementation could improve the response to the bacterial infection. To address this, we defined a non-antibiotic, non-cytotoxic concentration of selenium to evaluate its effect on the response to in vitro infections of SHK-1 cells with P. salmonis. The results indicated that selenium supplementation reduced the cytopathic effect, intracellular bacterial load, and cellular mortality of SHK-1 by increasing the abundance and activity of host glutathione peroxidase. We then prepared diets supplemented with selenium up to 1, 5, and 10 mg/kg to feed juvenile trout for 8 weeks. At the end of this feeding period, we obtained their blood plasma and evaluated its ability to protect SHK-1 cells from infection with P. salmonis in ex vivo assays. These results recapitulated the observed ability of selenium to protect against infection with P. salmonis by increasing the concentration of selenium and the antioxidant capacity in fish’s plasma. To the best of our knowledge, this is the first report of the protective capacity of selenium against P. salmonis infection in salmonids, becoming a potential effective host-directed dietary therapy for SRS and other infectious diseases in animals at a non-antibiotic concentration.

Transcriptomic Diversity in the Livers of South African Sardines Participating in the Annual Sardine Run

During austral winter, the southern and eastern coastlines of South Africa witness one of the largest animal migrations on the planet, the KwaZulu-Natal sardine run. Hundreds of millions of temperate sardines, Sardinops sagax, form large shoals that migrate north-east towards the subtropical Indian Ocean. Recent studies have highlighted the role that genetic and environmental factors play in sardine run formation. In the present study, we used massively parallel sequencing to assemble and annotate the first reference transcriptome from the liver cells of South African sardines, and to investigate the functional content and transcriptomic diversity. A total of 1,310,530 transcripts with an N50 of 1578 bp were assembled de novo. Several genes and core biochemical pathways that modulate energy production, energy storage, digestion, secretory processes, immune responses, signaling, regulatory processes, and detoxification were identified. The functional content of the liver transcriptome from six individuals that participated in the 2019 sardine run demonstrated heterogeneous levels of variation. Data presented in the current study provide new insights into the complex function of the liver transcriptome in South African sardines.

Dual effect of selenium loaded chitosan nanoparticles on growth, antioxidant, immune related genes expression, transcriptomics modulation of caspase 1, cytochrome P450 and heat shock protein and Aeromonas hydrophila resistance of Nile Tilapia (Oreochromis niloticus)

Nowadays there is a great attention for nanotechnology in aquaculture production. It has an efficient role in nutrients and drugs delivery, ponds sterilization, water treatment and aquatic diseases reduction. Till now, there is no available data on impact of selenite-loaded chitosan nanoparticles (SeChNPs) on Nile tilapia. Hence, the current study investigated the effects of selenite-loaded chitosan nanoparticles supplementation on the growth, immune, antioxidant and apoptotic related genes as well as resistance to Aeromonas hydrophila of Nile tilapia, Oreochromis niloticus. A total of 400 fish were randomly divided into four groups, and each group retained five replicates. The control group was fed a basal diet (with inorganic se), other groups fed diets supplemented with SeChNPs 0.5, 1 and 2 g/kg diet. The loading concentration of Se to ChNPs was 0.3, 0.6 and 1.2 mg/0.5, 1 and 2 gm respectively. Fish groups fed SeChNPs (0.5 and 1 g/kg) exhibited the highest final body gain, better feed utilization. Additionally, the expression of myostatin gene was down-regulated by 0.2 and 0.3 fold in group fed 0.5 and 1 g/kg SeChNPs when compared with control group. Dietary inclusion of SeChNPs increased serum lysozyme, alternative complement and myeloperoxidase activities and immunoglobulin type M level. Supplementation of SeChNPs at the level of 2 g/kg up-regulated glutathione peroxidase, superoxide dismutase and catalase expression by 1.12, 4.9 and 2.31 folds respectively, in comparison with control group. In contrast, the levels of C- reactive protein and malondialdehyde were reduced. The expression of IL-10, IL-8, TNF-α and IL-1β genes was up-regulated after dietary inclusion of different levels of SeChNPs in a dose dependent manner. Post-challenge, the highest survival rate was detected in group fed 2 g/kg SeChNPs (93%) in contrast, the control group was displayed the lowest survival rate (45%). After challenge with A. hydrophila, the expression of caspase 1 was up-regulated in groups fed 1 and 2 g/kg of SeChNPs. Moreover, the maximum down-regulation of cytochromes P450 and heat shock protein were found in 2 g/kg SeChNPs supplemented group (reduced by 0.4 and 0.6-fold, respectively, when compared with control group). In conclusion, the ameliorative effects of SeChNPs on Nile tilapia growth resulted from immune stimulatory and free radicals scavenging effects of selenium loaded chitosan nano composite.

Selenium Nanoparticles and Spirulina Alleviate Growth Performance, Hemato-Biochemical, Immune-Related Genes, and Heat Shock Protein in Nile Tilapia (Oreochromis niloticus)

The present investigation aimed to evaluate the influence of selenium nanoparticles (Se-NPs) or/and spirulina (SP) on the growth, immunity, and oxidation resistance of Nile tilapia. Four groups of fish fed diets with Se-NPs or/and SP at 0 g (control), 1 g SP/kg diet (SP), 1 mg Se-NPs/kg diet (Se-NPs), and 1 g SP + 1 mg Se-NPs/kg diet (SP/Se-NPs) for 60 days. Fish fed Se-NPs or/and SP displayed significantly improved weight gain (WG) and decreased feed conversion ratio (P < 0.05). The highest WG has observed in fish fed both Se-NPs and SP, while the specific growth rate was improved by feeding Se-NPs only or both Se-NPs and SP (P < 0.05). Blood albumin was increased significantly with Se-NPs with regard to the control (P < 0.05), while there were no significant differences between fish fed Se-NPs or/and SP. Blood total protein also was improved by feeding Se-NPs only or both Se-NPs and SP (P < 0.05). Further, blood immunoglobulin M was increased by feeding both Se-NPs and SP (P < 0.05), while the differences were insignificantly differing with fish fed only Se-NPs (P > 0.05). The transcription of liver superoxide dismutase (SOD) and tumor necrosis factor-alpha (TNF-α) genes was upregulated significantly by Se-NPs or/and SP (P < 0.05). Interestingly, TNF-α was significantly upregulated by SP when compared to those fed Se-NPs only or both Se-NPs and SP. However, heat shock protein 70 (HSP70) gene transcription was downregulated by Se-NPs or/and SP (P < 0.05). Based on the measured parameters, the mixture of both Se-NPs and SP is highly recommended for the welfare of Nile tilapia.

MicroRNA-29b modulates the innate immune response by suppressing IFNγs production in orange-spotted grouper (Epinephelus coioides)

Interferon-γ (IFNγ), a type II interferon, is essential to host resistance against various infections. Unlike other vertebrates, fish have two types of IFNγs, IFNγ1 (also named IFNγ-rel) and IFNγ2. MicroRNAs (miRNAs) regulate multiple biological processes by suppressing mRNA translation or inducing mRNA degradation. Among them, miR-29 can directly target IFNγ and affact innate and adaptive immune responses in mice. There are five members of the miR-29 family in orange-spotted grouper (Epinephelus coioides), which share the same miRNA seed region. However, whether miR-29 directly targets E. coioides IFNγs and regulate IFNγ production is still unknown. In the present study, the negative correlation between miR-29b and both IFNγs in immune tissues of healthy E. coioides and grouper spleen cells (GS cells) stimulated with LPS or poly I:C was demonstrated. Moreover, dual-luciferase reporter assays and western blotting were performed to demonstrate that miR-29b suppressed E. coioides IFNγ production. Studies of NO production in GS cells after miR-29b transfection revealed that miR-29b overexpression affected NO production through the downregulation of IFNγ expression. Taken together, our results suggest that miR-29b may directly target E. coioides IFNγs and modulate IFNγ-mediated innate immune responses by suppressing E. coioides IFNγs production.

Parental Selenium Nutrition Affects the One-Carbon Metabolism and the Hepatic DNA Methylation Pattern of Rainbow Trout (Oncorhynchus mykiss) in the Progeny

Selenium is an essential micronutrient and its metabolism is closely linked to the methionine cycle and transsulfuration pathway. The present study evaluated the effect of two different selenium supplements in the diet of rainbow trout (Onchorhynchus mykiss) broodstock on the one-carbon metabolism and the hepatic DNA methylation pattern in the progeny. Offspring of three parental groups of rainbow trout, fed either a control diet (NC, basal Se level: 0.3 mg/kg) or a diet supplemented with sodium selenite (SS, 0.8 mg Se/kg) or hydroxy-selenomethionine (SO, 0.7 mg Se/kg), were collected at swim-up fry stage. Our findings suggest that parental selenium nutrition impacted the methionine cycle with lower free methionine and S-adenosylmethionine (SAM) and higher methionine synthase (mtr) mRNA levels in both selenium-supplemented treatments. DNA methylation profiling by reduced representation bisulfite sequencing (RRBS) identified differentially methylated cytosines (DMCs) in offspring livers. These DMCs were related to 6535 differentially methylated genes in SS:NC, 6890 in SO:NC and 7428 in SO:SS, respectively. Genes with the highest methylation difference relate, among others, to the neuronal or signal transmitting and immune system which represent potential targets for future studies.

Bioremediation of Aquaculture Wastewater with Algal-Bacterial Biofilm Combined with the Production of Selenium Rich Biofertilizer

The discharge of aquaculture wastewater and the excessive selenium in aquaculture effluent caused by selenium addition to aquatic feed are posing a serious risk for the marine environment. In this study, batch tests were carried out to investigate the feasibility of utilizing algal–bacterial biofilm for the treatment of selenium-rich aquaculture wastewater. The effects of four different types of commercial biofilm carriers on the attached growth of biofilms and the contaminant removal capacity were examined. The braided cotton biofilm carrier had the best performance on biofilm growth, while in an exponential growth period the dry weight density of the biofilm was above 2.0 g L−1. By utilizing the braided cotton carrier with a hydraulic retention time (HRT) of 6 days, the removal rate of N and P from the raw aquaculture wastewater was 88.5 ± 6.2% and 99.8 ± 0.2%, respectively. After that, the effects of different initial wastewater load ratios (IWLR) and HRT on the effluent quality of the treatment process were studied. The decrease in IWLR and the extension of HRT could improve the treatment performance. The effluent N, P and Se concentrations in the group with 50% IWLR and 6-day HRT were 0.75 ± 0.10 mg L−1, 0.015 ± 0.02 mg L−1, 35.2 ± 3.2 μg L−1, respectively, indicating an effective removal of the main contaminants. The algal–bacterial biofilm harvested from the batch test was rich in N, P and Se, where the Se content was 21.8 ± 3.4 mg kg−1, which has the potential to be used as an Se-rich biofertilizer.

Diets supplemented with Saccharina latissima influence the expression of genes related to lipid metabolism and oxidative stress modulating rainbow trout (Oncorhynchus mykiss) fillet composition

This study aimed to evaluate the impact of diets including increasing amounts (1, 2 and 4%) of an iodine-rich macroalgae, Saccharina latissima, on gene expression and fillet composition of commercial-sized rainbow trout. Liver and muscle expression of genes related to growth, iodine, oxidative stress, and lipid metabolism, and the fillet content of fatty acids, cholesterol, and vitamin D3 were assessed. The highest kelp inclusion led to lower final body weight and HSI, without significant differences in mRNA transcription of genes involved in growth (ghr1, ghr2 and igf1) or iodine metabolism (dio1, thra, and thrb). A significant downregulation of an oxidative stress marker, gpx1b2, was observed in fish fed 2% S. latissima, which might suggest the need for less endogenous antioxidants. Dietary inclusion of kelp impacted lipid metabolism, with a downregulation of fatty acid synthase, accompanied by a general decrease of fatty acids in fillet. The present study demonstrated that supplementation of diets with 1 or 2% S. latissima can be achieved without detrimental effects on rainbow trout final weight. Evidence suggest a lipid-lowering effect of diets that did not compromise fillet EPA and DHA concentrations, being 3.7 times above the recommended levels for human consumption.

Synergistic Effects of Selenium Nanoparticles and Vitamin E on Growth, Immune-Related Gene Expression, and Regulation of Antioxidant Status of Nile Tilapia (Oreochromis niloticus)

The present study was conducted to investigate the effects of nano-selenium (Nano Se) or/and vitamin E (VE) on growth performance, blood health, intestinal histomorphology, oxidative status, and immune-related gene expression of Nile tilapia. Nano Se or/and VE at a rate of 0, 1 mg Nano Se/kg, 100 mg VE/kg, and 1 mg Nano Se/kg + 100 mg VE diet were fed to fish for 8 weeks. FBW was significantly (P < 0.05) increased in fish fed with Nano Se and VE, while fish fed with Nano Se or Nano Se and VE diets displayed significantly (P < 0.05) higher WG and SGR than the other groups. The lowest FCR was significantly (P < 0.05) detected in fish fed with Nano Se and VE, while the highest value was observed in fish VE diet. The intestinal morphometry (villi length and width) of fish fed with Nano Se or/and VE reported significantly (P < 0.05) the highest values with high number of goblet cells. Blood hematology and biochemistry parameters of fish fed with Nano Se or/and VE showed normal values with insignificant differences except for the blood total protein increased in fish fed with Nano Se or/and VE (P < 0.05). Dietary Nano Se or Nano Se and VE significantly (P < 0.05) increased the GPX, SOD, CAT, NBT, lysozyme, and phagocytosis values with decreased MDA. Liver and spleen TNF-α and IL-1β expressions were significantly (P < 0.05) upregulated in fish fed on Nano Se or Nano Se and VE. Thus, Nano Se or/and VE can be used effectively in tilapia diets for improving the growth, intestinal health, blood health, oxidative status, and immune-related gene expression.

The hepatic transcriptome of the turkey poult (Meleagris gallopavo) is minimally altered by high inorganic dietary selenium

There is interest in supplementing animals and humans with selenium (Se) above Se-adequate levels, but the only good biomarker for toxicity is tissue Se. We targeted liver because turkeys fed 5 μg Se/g have hepatic Se concentrations 6-fold above Se-adequate (0.4 μg Se/g) levels without effects on growth or health. Our objectives were (i) to identify transcript biomarkers for high Se status, which in turn would (ii) suggest proteins and pathways used by animals to adapt to high Se. Turkey poults were fed 0, 0.025, 0.4, 0.75 and 1.0 μg Se/g diet in experiment 1, and fed 0.4, 2.0 and 5.0 μg Se/g in experiment 2, as selenite, and the full liver transcriptome determined by RNA-Seq. The major effect of Se-deficiency was to down-regulate expression of a subset of selenoprotein transcripts, with little significant effect on general transcript expression. In response to high Se intake (2 and 5 μg Se/g) relative to Se-adequate turkeys, there were only a limited number of significant differentially expressed transcripts, all with only relatively small fold-changes. No transcript showed a consistent pattern of altered expression in response to high Se intakes across the 1, 2 and 5 μg Se/g treatments, and there were no associated metabolic pathways and biological functions that were significant and consistently found with high Se supplementation. Gene set enrichment analysis also found no gene sets that were consistently altered by high-Se and supernutritional-Se. A comparison of differentially expressed transcript sets with high Se transcript sets identified in mice provided high Se (~3 μg Se/g) also failed to identify common differentially expressed transcript sets between these two species. Collectively, this study indicates that turkeys do not alter gene expression in the liver as a homeostatic mechanism to adapt to high Se.

The potential role of nano-selenium and vitamin C on the performances of Nile tilapia (Oreochromis niloticus)

Functional trace elements and vitamins can boost immunity and antioxidative response in aquatic animals without creating environmental hazards. While nano-selenium (Nano-Se) and vitamin C (VC) have been used as immunomodulators and antioxidants in animal and poultry feed, there is little data on Nano-Se and/or VC supplementation in aquatic animals. Thus, the current study evaluated the impact of adding Nano-Se and VC to the diets of Nile tilapia for 8 weeks. Four diets were formulated and offered to the fish: no supplementation (control), 1 mg Nano-Se/kg, 500 mg VC/kg, and 1 mg Nano-Se + 500 mg VC/kg of food. Growth-related parameters (final body weight, weight gain, and specific growth rate) were significantly increased in tilapia fed Nano-Se and VC, with a reduced feed conversion ratio (P < 0.05). Intestinal villus length and width as well as the number of goblet cells were increased in tilapia fed Nano-Se and/or VC (P < 0.05). Additionally, dietary Nano-Se and/or VC significantly increased nitro-blue tetrazolium (NBT) level, superoxide dismutase, glutathione peroxidase, catalase, the phagocytic index, and lysozyme and phagocytic activities (P < 0.05). However, significantly reduced levels of malonaldehyde were observed in fish fed Nano-Se and/or VC (P < 0.05). TNF-α and IL-1β gene expressions in the liver and spleen of the fish were significantly upregulated by Nano-Se and/or VC (P < 0.05). The results revealed the potential role of Nano-Se and/or VC in enhancing growth, intestinal morphometry, and immune and antioxidative responses in Nile tilapia.

Subchronic effects of dietary selenium yeast and selenite on growth performance and the immune and antioxidant systems in Nile tilapia Oreochromis niloticus

Selenium is an essential element but toxic at high levels in animals. The effects of Se on growth performance and the immune system in Nile tilapia remain inconclusive. In this study, Nile tilapia Oreochromis niloticus was fed on selenium yeast (Se(Y))- and selenite (Se(IV))-enriched feed at 0, 3, 6, and 12 μg/g (dry wt) for 45 and 90 d. The growth, bioaccumulation, biochemical markers related to antioxidant, immunological, nervous and digestive systems were evaluated in various fish tissues (liver, intestine, kidney, muscle, brain, spleen, gills). The results showed that the accumulation of Se(Y) was 1.3-2 folds of Se(IV) in most tissues. The growth of tilapia was enhanced by both Se(Y) and Se(IV) at 3 μg/g after 90 d, with Se(Y) better than Se(IV) in tilapia feed. After 45 d, the levels of lipid peroxidation, the activity of the antioxidant enzymes, and the transcriptional levels of the immune related genes (IL-1β, IFN-γ and TNF-α) and stress proteins (HSP70 and MT) were enhanced in all treatments, except that of MT in the 12 μg/g Se(Y) group. In addition, both Se species inhibited the activity of acetylcholinesterase (AChE) in the brain and one digestive enzyme α-glucosidase (α-Glu) in the intestine at 12 μg/g. However, after 90 d, the effects on most biochemical markers were less pronounced, implying a possible acclimation after prolonged duration. The results demonstrate Se is beneficial to O. niloticus at low levels and toxic at elevated levels. The immunostimulation by Se might be greatly weakened after long term feeding Se-enriched feed. This study helps to better understand the effects of Se on the antioxidant and immune systems and to establish the optimal Se levels in the feed and duration for O. niloticus.

Can inorganic elements affect herpesvirus infections in European eels?

In combination, pollution and pathogens represent a serious threat to the health of European eels that has been increasingly recognized. Thus, the impact of contaminants, cadmium, lead, mercury, and selenium, on anguillid herpesvirus 1 infection in wild European eels has been evaluated. Despite the small sample size, results indicate that selenium and mercury concentrations may compromise the European eel immune system as herpesvirus infection was more prevalent in specimens with higher Hg and Se hepatic concentrations.

Transcriptome profiling of posterior kidney of brown trout, Salmo trutta, during proliferative kidney disease

BACKGROUND

Tetracapsuloides bryosalmonae is a myxozoan parasite which causes economically important and emerging proliferative kidney disease (PKD) in salmonids. Brown trout, Salmo trutta is a native fish species of Europe, which acts as asymptomatic carriers for T. bryosalmonae. There is only limited information on the molecular mechanism involved in the kidney of brown trout during T. bryosalmonae development. We employed RNA sequencing (RNA-seq) to investigate the global transcriptome changes in the posterior kidney of brown trout during T. bryosalmonae development.

METHODS

Brown trout were exposed to the spores of T. bryosalmonae and posterior kidneys were collected from both exposed and unexposed control fish. cDNA libraries were prepared from the posterior kidney and sequenced. Bioinformatics analysis was performed using standard pipeline of quality control, reference mapping, differential expression analysis, gene ontology, and pathway analysis. Quantitative real time PCR was performed to validate the transcriptional regulation of differentially expressed genes, and their correlation with RNA-seq data was statistically analyzed.

RESULTS

Transcriptome analysis identified 1169 differentially expressed genes in the posterior kidney of brown trout, out of which 864 genes (74%) were upregulated and 305 genes (26%) were downregulated. The upregulated genes were associated with the regulation of immune system process, vesicle-mediated transport, leucocyte activation, and transport, whereas the downregulated genes were associated with endopeptidase regulatory activity, phosphatidylcholine biosynthetic process, connective tissue development, and collagen catabolic process.

CONCLUSION

To our knowledge, this is the first RNA-seq based transcriptome study performed in the posterior kidney of brown trout during active T. bryosalmonae development. Most of the upregulated genes were associated with the immune system process, whereas the downregulated genes were associated with other metabolic functions. The findings of this study provide insights on the immune responses mounted by the brown trout on the developing parasite, and the host molecular machineries modulated by the parasite for its successful multiplication and release.

An evaluation of dietary selenium nanoparticles for red sea bream (Pagrus major) aquaculture: growth, tissue bioaccumulation, and antioxidative responses

Selenium nanoparticles (Se-NPs) were added at 0, 0.5, 1, and 2 mg per kg diet to assess its effects on the performance, Se bioaccumulation, blood health, and antioxidant status of red sea bream. After 45 days, Se-NPs positively impacted the growth and feed efficiency of red sea bream especially by 1 mg per kg diet. No significant (P > 0.05) changes in survival and somatic indices were noticed among groups. Dietary Se-NPs significantly (P < 0.05) increased the protein, lipid, and Se contents in the whole body, muscle, and liver tissues, whereas decreasing the whole-body moisture content of treated groups compared with the Se-NP-free group. Using of Se-NPs at 2 mg per kg diet resulted in the highest Se content in the complete body, muscle, and liver. Significantly enhanced intestine protease activity and hematocrit levels accompanied with low cholesterol and triglyceride were observed in fish fed Se-NP-enriched diets. Fish fed on Se-NPs at 0.5, 1, and 2 mg Se-NPs per kg diet exhibited significantly higher values of biological antioxidant potential than the control group (P < 0.05). Therefore, the obtained results recommends adding 1 mg Se-NPs per kg diet to improve the growth, feed efficiency, blood health, and antioxidant defense system of red sea bream.

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.

Toxicity of dietary selenomethionine in juvenile steelhead trout, Oncorhynchus mykiss: tissue burden, growth performance, body composition, hematological parameters, and liver histopathology

The steelhead trout (Oncorhynchus mykiss) is the species most at risk from selenium (Se) exposure in the San Francisco Bay Delta (SFBD). However, although steelhead trout are usually exposed to environmental Se in the juvenile stage, data to test their sensitivity to excess Se, especially its organic form, in the juvenile stage are scarce. Therefore, the objective of the current study was to assess the sensitivity of juvenile steelhead trout to ecologically relevant forms of Se using integrated sensitive endpoints. Fish (mean weight: 22.3 g) were fed one of five diets containing 1.1 (control), 8.8, 15.4, 30.8, and 61.6 μg Se/g diet dw (Se1.1, Se8.8, Se15.4, Se30.8, and Se61.6, respectively) in the form of selenomethionine for 4 weeks. After 4 weeks, Se significantly accumulated in a dose-dependent manner in all tissues at different rates. The growth rate and plasma cholesterol were significantly depressed in fish fed diets containing Se30.8 and above. Hematological parameters and mortality were significantly elevated in fish fed the Se61.6 diet. Marked histopathological alterations were observed in fish fed the Se8.8 diet (the lowest observed effect concentration, LOEC) and above. The current results suggest that the steelhead trout is more sensitive to excess Se than nonanadromous rainbow trout used in previous studies because of its lower LOEC despite the use of selenomethionine and the shorter experimental duration. Additionally, it should be noted that the current Se levels found in the SFBD are already a threat to the threatened population of steelhead trout on the central California coast.

Four selenoprotein P genes exist in salmonids: Analysis of their origin and expression following Se supplementation and bacterial infection

The following research was conducted to elucidate the evolution and expression of salmonid selenoprotein P (SelP), a selenoprotein that is unique in having multiple selenocysteine (Sec) residues, following supranutritional selenium supplementation and infection in rainbow trout. We show that in salmonids SelP is present as four paralogues and that the diversification of SelP genes during vertebrate evolution relates to whole genome duplication events. With 17 and 16 selenocysteine residues for rainbow trout (Oncorhynchus mykiss)/Atlantic salmon (Salmo salar) SelPa1 and SelPa2 proteins respectively and 1 or 2 (trout or salmon) and 4 or 3 (trout or salmon) selenocysteine residues for salmonid SelPb1 and SelPb2 proteins respectively, this is the highest number of (predicted) multiple selenocysteine containing SelP proteins reported for any vertebrate species to date. To investigate the effects of selenium form on SelP expression we added different concentrations (1 nM– 10 μM) of organic or inorganic selenium to a trout cell line (RTG-2 cells) and analysed changes in mRNA abundance. We next studied the impact of supplementation on the potential modulation of these transcripts by PAMPs and proinflammatory cytokines in RTG-2 and RTS-11 cells. These experiments revealed that selenium type influenced the responses, and that SelP gene subfunctionalisation was apparent. To get an insight into the expression patterns in vivo we conducted a feeding trial with 2 diets differing in selenium content and 5 weeks later challenged the trout with a bacterial pathogen (Aeromonas salmonicida). Four tissues were analysed for SelP paralogue expression. The results show a significant induction of SelPa1 in gills and intestine following infection in selenium supplemented fish and for SelPa2 in gills. SelPb1 was significantly reduced in head kidney of both diet groups following infection, whilst SelPb2 was significantly upregulated in skin of both diet groups post infection. Overall these findings reveal differential expression profiles for the SelPa/SelPb paralogues in trout, influenced by selenium supply, cell type/tissue and stimulant. The increase of multiple Sec containing SelP proteins in salmonids could indicate an enhanced requirement for selenium in this lineage.

β-1, 3 glucan binding protein based selenium nanowire enhances the immune status of Cyprinus carpio and protection against Aeromonas hydrophila infection

In the present study, immunoenhancing effect of β-1, 3 glucan binding protein based selenium nanowire (Phβ-GBP-SeNWs) in common carp, Cyprinus carpio was assessed. Biological based selenium nanoform was synthesized, using crustacean immune molecule β-GBP purified from the haemolymph of Paratelphusa hydrodromus. The morphological property of Phβ-GBP-SeNWs was analyzed through TEM which reveals, the synthesized nanowire exhibits approximately 30-50 nm width with smooth surface. For this current study, fish were fed with experimental diet includes Phβ-GBP, sodium selenite, selenomethionine and Phβ-GBP-SeNWs supplemented diet at different concentrations (0.5 mg, 1 mg and 2 mg) for 30 days. The growth performance, cellular and humoral immune responses (myeloperoxidase, reactive oxygen species, alkaline phosphatase and lysozyme activity) and antioxidant enzymes (glutathione peroxidase and catalase activity) in the fish fed with Phβ-GBP-SeNWs supplemented diet were significantly increased in dose-dependent manner, which was observed at two different interval period (15^th and 30^th day). Also, Phβ-GBP-SeNWs supplemented diet fed fish gain resistant after challenged with aquatic pathogen Aeromonas hydrophila and the relative survival percentage was increased. Agar disc diffusion and BacLight assay clearly demonstrated the antibacterial property of plasma of fish fed with Phβ-GBP-SeNWs supplemented diet against aquatic pathogen A. hydrophila, Vibrio parahaemolyticus and Vibrio alginolyticus. Moreover, confocal laser scanning microscopic analysis clearly showed that, Phβ-GBP-SeNWs supplemented diet fed fish plasma was more efficient in disrupting the architecture of bacterial colonies and thereby reduced the thickness of biofilm. Thus, the present study indicates that, incorporation of Phβ-GBP-SeNWs in the diet enhances the fish immune responses and disease resistance against aquatic pathogens.

Selenium deficiency impaired structural integrity of the head kidney, spleen and skin in young grass carp (Ctenopharyngodon idella)

This study focused on the effects of dietary selenium deficiency on structural integrity of the head kidney, spleen and skin in young grass carp (Ctenopharyngodon idella). A total of 540 healthy grass carp (mean weight 226.48 ± 0.68 g) were randomly divided into six groups and fed six separate diets with graded dietary levels of selenium (0.025-1.049 mg/kg diet) for 80 days. Results showed that selenium deficiency (1) caused oxidative damage in part by reducing the activities of antioxidant enzymes (such as SOD, CAT, GPx, GST and GR) and glutathione (GSH) content, down-regulating the transcript abundances of antioxidant enzymes (except GSTp1) partly related to Kelch-like-ECH-associated protein 1a (Keap1a)/NF-E2-related factor 2 (Nrf2) signalling; (2) aggravated apoptosis in part by up-regulating the mRNA levels of caspase-2, -3, -7, -8 and -9, which were partially related to p38MAPK/FasL/caspase-8 signalling and JNK/(BAX, Bcl-2, Mcl-1b, IAP)/(Apaf1, caspase-9) signalling; (3) damaged the tight junctions in part by down-regulating the mRNA levels of ZO-1 (except spleen), ZO-2 (except spleen), claudin-c, -f, -7, -11 and claudin-15, and up-regulating the mRNA levels of claudin-12, which were partially related to myosin light chain kinase (MLCK) signalling. Interesting, selenium deficiency failed to affect the expression of GSTp1, Keap1a, occludin, claudin-b, claudin-3c, ZO-1 (spleen only) and ZO-2 (spleen only) in the head kidney, spleen and skin of grass carp. Finally, based on the activities of glutathione peroxidase (GPx) and reactive oxygen species (ROS) content in the head kidney, spleen and skin, the dietary selenium requirements for young grass carp were estimated to be 0.558-0.588 mg/kg diet.

Selenium deficiency impaired immune function of the immune organs in young grass carp (Ctenopharyngodon idella)

This study aimed to investigate the effects of dietary selenium on resistance to skin haemorrhages and lesions and on immune function as well as the underlying mechanisms of those effects in the head kidney, spleen and skin of young grass carp (Ctenopharyngodon idella). A total of 540 healthy grass carp with initial body weight (226.48 ± 0.68 g) were randomly divided into six groups and fed six separate diets with graded dietary levels of selenium (0.025, 0.216, 0.387, 0.579, 0.795 and 1.049 mg/kg diet) for 80 days. After the feeding period, an immunization trial was performed by infection with Aeromonas hydrophila for 14 days. The results showed that, compared with the optimal selenium level, (1) selenium deficiency impaired the production of antibacterial compounds and immunoglobulins and down-regulated the transcript abundances of antimicrobial peptides and selenoproteins; (2) selenium deficiency aggravated inflammatory responses in part by up-regulating pro-inflammatory cytokines and down-regulating anti-inflammatory cytokines mRNA levels, which were partially related to [IKKα, β, γ/IκBα/NF-κB] signalling and [TOR/(S6K1, 4E-BP1)] signalling, respectively. Interestingly, selenium deficiency had no effect on the expression of TGF-β2, IL-4/13B, IL-10, IL-12p35, IL-15 (skin only) or 4E-BP2 in the head kidney, spleen and skin of young grass carp. Finally, based on the percent weight gain (PWG), the morbidity of skin haemorrhages and lesions, the ACP activity in the head kidney and the lysozyme activity in spleen, the optimal dietary selenium requirements for young grass carp were estimated to be 0.546-0.604 mg/kg diet. In summary, selenium deficiency decreased the growth performance and impaired the immune function in the head kidney, spleen and skin of young grass carp.

Selenium-Chromium(VI) Interaction Regulates the Contents and Correlations of Trace Elements in Chicken Brain and Serum

This study aims to investigate the contents of trace elements in the brain and serum of male chickens and the effect of selenium-chromium(VI) interaction. A chronic experimental model was established by supplementing 22.14 mg/kg K₂Cr₂O₇ with 0.00, 0.31, 0.63, 1.25, 2.50, and 5.00 mg/kg Na₂SeO₃ mg/kg B.W. to water for chicken daily. After 14, 28, and 42 days of exposure to the solution, the brain and serum of chickens from each group were collected to detect the levels of Ca, Cu, Mn, Fe, Zn, and Mg by inductively coupled plasma mass spectrometer (ICP-MS). Cr(VI) time-dependently accumulated in the brain and serum. The contents of Cr increased both in the brain and serum with prolonged exposure. Cr contents in the brain and serum decreased in all Se groups compared with those in only Cr-treated groups. Ca contents decreased with prolonged exposure and increasing Se dosage. The contents of Cu and Mn increased on the 28th day but decreased on the 42nd day in the brain and serum. Fe and Zn contents decreased in the serum under prolonged exposure and increased on the 28th day but decreased on the 42nd day in the brain. Cr exposure did not significantly affect Mg contents in the brain but slightly decreased those in the serum. Therefore, appropriate doses of Se affected Cr accumulation, leading to adjustments in the contents and correlations of trace elements.

Sensitivity and toxic mode of action of dietary organic and inorganic selenium in Atlantic salmon (Salmo salar)

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±7g) that were fed organic and inorganic Se fortified diets. Atlantic salmon were fed a low natural background organic Se diet (0.35mg Se kg^-1, wet weight (WW)) fortified with inorganic sodium selenite or organic selenomethionine-yeast (SeMet-yeast) at two levels (∼1-2 or 15mgkg^-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 15mgkg^-1 selenite, but not 15mgkg^-1 SeMet-yeast, showed reduced feed intake, reduced growth, increased liver TBARS and reduced liver tocopherol. Main metabolic pathways significantly affected by 15mgkg^-1 selenite, and to a lesser extent 15mgkg^-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 2.1mgkg^-1 selenite and SeMet-yeast did not affect any of the above mentioned parameters. Apparent toxic mechanisms at higher Se levels (15mgkg^-1) included oxidative stress and altered lipid metabolism for both inorganic and organic Se, with higher toxicity for inorganic Se.

Nutrigenomics and immune function in fish: new insights from omics technologies

The interplay between nutrition and immune system is well recognised, however the true integration of research between nutrition, animal energy status and immune function is still far from clear. In fish nutrition, especially for species maintained in aquaculture, formulated feeds are significantly different from the natural diet with recent changes in nutrient sources, especially with protein and oil sources now being predominated by terrestrial derived ingredients. Additionally, many feeds are now incorporated to health management and termed functional feeds, which are believed to improve fish health, reduce disease outbreaks and/or improve post-infection recovery. Using new omics technologies, including transcriptomics (microarray and RNA-seq) and proteomics, the impacts of nutrition on the immune system is becoming clearer. By using molecular pathway enrichment analysis, modules of genes can indicate how both local (intestinal) and systemic immune function are being altered. Although great progress has been made to define the changes in host immune function, understanding the interplay between fish nutrition, intestinal microbiome and immune system is only just beginning to emerge.

Omics and cytokine discovery in fish: Presenting the Yellowtail kingfish (Seriola lalandi) as a case study

A continued programme of research is essential to overcome production bottlenecks in any aquacultured fish species. Since the introduction of genetic and molecular techniques, the quality of immune research undertaken in fish has greatly improved. Thousands of species specific cytokine genes have been discovered, which can be used to conduct more sensitive studies to understand how fish physiology is affected by aquaculture environments or disease. Newly available transcriptomic technologies, make it increasingly easier to study the immunogenetics of farmed species for which little data exists. This paper reviews how the application of transcriptomic procedures such as RNA Sequencing (RNA-Seq) can advance fish research. As a case study, we present some preliminary findings using RNA-Seq to identify cytokine related genes in Seriola lalandi. These will allow in-depth investigations to understand the immune responses of these fish in response to environmental change or disease and help in the development of therapeutic approaches.

Russian sturgeon cultured in a subtropical climate shows weaken innate defences and a chronic stress response

Russian sturgeon (Acipenser gueldenstaedtii) has been successfully farmed in Uruguay for the past ten years. However, during the Uruguayan summer fish endure high water temperatures and increased bacterial infections that threaten aquaculture. Our understanding of sturgeon's immune system and its interplay with environmental factors like temperature is almost unknown. This study analysed the way in which seasonal variations affect enzymatic blood components of Russian sturgeon's innate defences, including the serum alternative complement pathway (ACP), ceruloplasmin (Cp) and lysozyme activities. Results showed that summertime conditions in the farm altered these defences in different ways, inducing a significant decrease in ACP and Cp, and an increase in lysozyme. In addition, serum levels of total protein and cortisol decreased in summer, suggesting a chronic stress response was induced in parallel. Subsequently, we analysed whether the increase in water river temperature during summer could account for the observed results. To that end, we acclimated juvenile sturgeons to mild (18 °C) or warm (24 °C) temperatures for 37 days. Like in summer, sturgeons exposed to 24 °C showed lower levels of serum ACP, Cp and total proteins, together with a progressive decrease in body weight and increased fish mortality. Administration of an immunostimulant containing Se and Zn slightly reverted the temperature-induced effects on sturgeon's defences. Altogether, our study provides novel data on various physiological parameters of the Russian sturgeon and highlights the impact warm temperature has on stress and innate immunity in this chondrostean fish.

Selenium nanoparticle-enriched biomass of Yarrowia lipolytica enhances growth and survival of Artemia salina

Controlling disease outbreaks is a major challenge in aquaculture farms and conventional methods are often ineffective. Nutritional supplementation and probiotic preparations help in reducing severity of such infections. The generally regarded as safe yeast (Yarrowia lipolytica) was used in the current study. A marine strain of Y. lipolytica exhibited tolerance towards sodium selenite and formed cell associated selenium nanoparticles (SeNPs). The synthesized nanoparticles were characterized by UV-vis spectroscopy, X-ray diffraction (XRD) and Field Emission Scanning Electron Microscope (FE-SEM) observations. Fourier transform infra-red (FTIR) spectroscopy indicated the role of carboxylic and amine groups in the synthesis of nanoparticles. This SeNP-enriched biomass was used as feed for the model aquaculture system, Artemia salina and compared with normal feed, baker's yeast (Saccharomyces cerevisiae). A. salina fed with SeNP-enriched biomass, showed increased survival rates (96.66%) as compared to those fed with S. cerevisiae (60.0%). The size of the larvae fed with SeNP-enriched biomass of Y. lipolytica was also found to be larger. Additionally, larval groups fed with SeNP-enriched biomass were better protected (70.0% survival) against V. harveyi infection when compared with groups fed with S. cerevisiae (24.44%). This combination of selenium in the nanoparticle form associated with the biomass of Y. lipolytica has potential application in improving health of aquaculture species in farms.

Changing expression of vertebrate immunity genes in an anthropogenic environment: a controlled experiment

Background

The effect of anthropogenic environments on the function of the vertebrate immune system is a problem of general importance. For example, it relates to the increasing rates of immunologically-based disease in modern human populations and to the desirability of identifying optimal immune function in domesticated animals. Despite this importance, our present understanding is compromised by a deficit of experimental studies that make adequately matched comparisons between wild and captive vertebrates.

Results

We transferred post-larval fishes (three-spined sticklebacks), collected in the wild, to an anthropogenic (captive) environment. We then monitored, over 11 months, how the systemic expression of immunity genes changed in comparison to cohort-matched wild individuals in the originator population (total n = 299). We found that a range of innate (lyz, defbl2, il1r-like, tbk1) and adaptive (cd8a, igmh) immunity genes were up-regulated in captivity, accompanied by an increase in expression of the antioxidant enzyme, gpx4a. For some genes previously known to show seasonality in the wild, this appeared to be reduced in captive fishes. Captive fishes tended to express immunity genes, including igzh, foxp3b, lyz, defbl2, and il1r-like, more variably. Furthermore, although gene co-expression patterns (analyzed through gene-by-gene correlations and mutual information theory based networks) shared common structure in wild and captive fishes, there was also significant divergence. For one gene in particular, defbl2, high expression was associated with adverse health outcomes in captive fishes.

Conclusion

Taken together, these results demonstrate widespread regulatory changes in the immune system in captive populations, and that the expression of immunity genes is more constrained in the wild. An increase in constitutive systemic immune activity, such as we observed here, may alter the risk of immunopathology and contribute to variance in health in vertebrate populations exposed to anthropogenic environments.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0751-8) contains supplementary material, which is available to authorized users.