Cytokine gene expression and prostaglandin production in head kidney leukocytes isolated from Atlantic cod (Gadus morhua) added different levels of arachidonic acid and eicosapentaenoic acid

Collectin-K1 Plays a Role in the Clearance of Streptococcus agalactiae in Nile Tilapia (Oreochromis niloticus)

Collectin-K1 (CL-K1) is a multifunctional C-type lectin that has been identified as playing a crucial role in innate immunity. It can bind to carbohydrates on pathogens, leading to direct neutralization, agglutination, and/or opsonization, thereby inhibiting pathogenic infection. In this study, we investigated a homolog of CL-K1 (OnCL-K1) in Nile tilapia (Oreochromis niloticus) and its role in promoting the clearance of the pathogen Streptococcus agalactiae (S. agalactiae) and enhancing the antibacterial ability of the fish. Our analysis of bacterial load displayed that OnCL-K1 substantially reduced the amount of S. agalactiae in tissues of the liver, spleen, anterior kidney, and brain in Nile tilapia. Furthermore, examination of tissue sections revealed that OnCL-K1 effectively alleviated tissue damage and inflammatory response in the liver, anterior kidney, spleen, and brain tissue of tilapia following S. agalactiae infection. Additionally, OnCL-K1 was found to decrease the expression of the pro-inflammatory factor IL-6 and migration inhibitor MIF, while increasing the expression of anti-inflammatory factor IL-10 and chemokine IL-8 in the spleen, anterior kidney, and brain tissues of tilapia. Moreover, statistical analysis of survival rates demonstrated that OnCL-K1 significantly improved the survival rate of tilapia after infection, with a survival rate of 90%. Collectively, our findings suggest that OnCL-K1 plays a vital role in the innate immune defense of resisting bacterial infection in Nile tilapia. It promotes the removal of bacterial pathogens from the host, inhibits pathogen proliferation in vivo, reduces damage to host tissues caused by pathogens, and improves the survival rate of the host.

Resveratrol impacts on aquatic animals: a review

Aquaculture has intensified tremendously with the increasing demand for protein sources as the global population grows. However, this industry is plagued with major challenges such as poor growth performance, the lack of a proper environment, and immune system impairment, thus creating stress for the aquaculture species and risking disease outbreaks. Currently, prophylactics such as antibiotics, vaccines, prebiotics, probiotics, and phytobiotics are utilized to minimize the negative impacts of high-density farming. One of the promising prophylactic agents incorporated in fish feed is resveratrol, a commercial phytophenol derived via the methanol extraction method. Recent studies have revealed many beneficial effects of resveratrol in aquatic animals. Therefore, this review discusses and summarizes the roles of resveratrol in improving growth performance, flesh quality, immune system, antioxidant capacity, disease resistance, stress mitigation, and potential combination with other prophylactic agents for aquatic animals.

Trophodynamics of the Antarctic toothfish (Dissostichus mawsoni) in the Antarctic Peninsula: Ontogenetic changes in diet composition and prey fatty acid profiles

The Antarctic toothfish (Dissostichus mawsoni) is the largest notothenioid species in the Southern Ocean, playing a keystone role in the trophic web as a food source for marine mammals and a top predator in deep-sea ecosystems. Most ecological knowledge on this species relies on samples from areas where direct fishing is allowed, whereas in areas closed to fishing, such as the Antarctic Peninsula (AP), there are still key ecological gaps to ensure effective conservation, especially regarding our understanding of its trophic relationships within the ecosystem. Here, we present the first comprehensive study of the feeding behavior of Antarctic toothfish caught in the northern tip of the AP, during two consecutive fishing seasons (2019/20 and 2020/21). Stomach content was analyzed according to size-classes, sex and season. Macroscopic morphological analysis was used to identify prey, whereas DNA analysis was used in highly digested prey items. Fatty acid analysis was conducted to determine the prey's nutritional composition. The diet mainly consisted of Macrouridae, Cephalopoda, Anotopteridae, and Channichthyidae. Other prey items found were crustaceans and penguin remains; however, these were rare in terms of their presence in stomach samples. Sex had no effect on diet, whereas size-class and fishing season influenced prey composition. From 27 fatty acid profiles identified, we observed two different prey groups of fishes (integrated by families Anotopteridae, Macrouridae and Channichthyidae) and cephalopods. Our results revealed a narrow range of prey items typical of a generalist predator, which probably consumes the most abundant prey. Understanding the diet and trophic relationships of Antarctic toothfish is critical for a better comprehension of its role in the benthic-demersal ecosystem of the AP, key for ecosystemic fisheries management, and relevant for understanding and predicting the effect of climate change on this species.

Hepatopancreas immune response during different photoperiods in the Chinese mitten crab, Eriocheir sinensis

Photoperiod plays an important role in the growth, development, and metabolism of crustaceans. The growth and reproduction of crabs are closely related to the photoperiod. The hepatopancreas is an important source of innate immune molecules; however, hepatopancreatic patterns of gene expression depending on the photoperiod-which may underlie changes in immune mechanisms-remain unknown. To study the molecular basis of immune regulation in the Chinese mitten crab (Eriocheir sinensis) under different light conditions, a new generation of high-throughput Illumina sequencing technology was used, and functional genes associated with immune function in the hepatopancreas of this crab were explored via assembly of high-quality sequences, gene annotation, and classification. A total of 383,899,798 clean reads from the hepatopancreas of the normal group (12 h/12 h L:D), 387,936,676 clean reads from the continuous light group (24 h/0 h L:D), and 384,872,734 clean reads from the continuous darkness group (0 h/24 h L:D) were obtained. Compared with the normal group, 141, 152, 60, 87, 90, and 101 differentially expressed genes were identified in the groups exposed to continuous light for 2 days, continuous darkness for 2 days, continuous light for 4 days, continuous darkness for 4 days, continuous light for 6 days, and continuous darkness for 6 days, respectively. The results of this study revealed that under continuous light and dark conditions, the crabs were most affected by light on day 2, but the interference gradually decreased with time. We suggest that long-term light or dark treatment makes crabs adaptable to fluctuations in the photoperiod. The expression of genes associated with immune response patterns was found to change during different photoperiods. Prophenoloxidase (proPO) and serine proteinase (kazal-type serine proteinase inhibitor 1 and serine proteinase inhibitor-3) in the proPO-activating system were significantly upregulated in the 2-day continuous light group. Glutathione peroxidase 3 was significantly downregulated under continuous light exposure, while cyclooxygenase was upregulated in the continuous light and dark environments. These results provide insights into the molecular mechanism underlying the effects of the photoperiod on immune regulation and the physiological activity of E. sinensis.

Effects of dietary arachidonic acid (ARA) on immunity, growth and fatty acids of Apostichopus japonicus

As an important aquaculture species, improving the immunity of cultured Apostichopus japonicus (A. japonicus) is vital for its health in aquaculture farming. It has been shown that ARA is an important metabolite for A. japonicus infected by Vibrio splendidus. In this study, we aimed to determine the effects of dietary exogenous ARA on healthy sea cucumber cultures, including assessments of immunity, growth, and fatty acid content. Five experimental diets containing 0.01%, 0.29%, 0.46%, 0.70%, and 1.09% ARA were tested. The specific growth rate (SGR) of sea cucumbers did not be significantly affected by exogenous ARA diet groups. The results showed that dietary ARA between 0.49 and 1.09% notably improved the survival rate of sea cucumbers infected by Vibrio splendidus compared with the control group without exogenous ARA. The results also showed the effects of dietary ARA on immune-related genes, enzymes, and oxidation indices; most of the exogenous ARA significantly upregulated the mRNA expression of the genes NFκB, TLR, TLR3, TRAF6, Toll, and MyD88. The activities of ACP, AKP, and lysozyme increased in the 0.49-1.09% ARA groups, especially the dietary 0.49% ARA group. The SOD1 and NOS activities were enhanced by dietary ARA between 0.29 and 0.70%. Compared with the control, the MDA content increased, but the 0.49% ARA-diet group had a lower MDA content. Based on these data, 0.49-0.70% ARA significantly enhanced immunity in cultured A. japonicus. Exogenous 0.49% and 0.70% ARA also elevated the ARA, total PUFA and n-6 PUFA in the body walls. In conclusion, the appropriate exogenous ARA (0.49%-0.70%) in diets could improve immunity and fatty acid content considerably. The results provide basic evidence that ARA can serve a useful immune enhancer for A. japonicus aquaculture.

Tailoring freshwater diets towards boosted immunity and pancreas disease infection robustness in Atlantic salmon post smolts

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

Impact of dietary level and ratio of n-6 and n-3 fatty acids on disease progression and mRNA expression of immune and inflammatory markers in Atlantic salmon (Salmo salar) challenged with Paramoeba perurans

The aim of the study was to investigate the influence of dietary level and ratio of n-6/n-3 fatty acids (FA) on growth, disease progression and expression of immune and inflammatory markers in Atlantic salmon (Salmo salar) following challenge with Paramoeba perurans. Fish (80 g) were fed four different diets with different ratios of n-6/n-3 FA; at 1.3, 2.4 and 6.0 and one diet with ratio of 1.3 combined with a higher level of n-3 FA and n-6 FA. The diet with the n-6/n-3 FA ratio of 6.0 was included to ensure potential n-6 FA effects were revealed, while the three other diets were more commercially relevant n-6/n-3 FA ratios and levels. After a pre-feeding period of 3 months, fish from each diet regime were challenged with a standardized laboratory challenge using a clonal culture of P. perurans at the concentration of 1,000 cells L⁻¹. The subsequent development of the disease was monitored (by gross gill score), and sampling conducted before challenge and at weekly sampling points for 5 weeks post-challenge. Challenge with P. perurans did not have a significant impact on the growth of the fish during the challenge period, but fish given the feed with the highest n-6/n-3 FA ratio had reduced growth compared to the other groups. Total gill score for all surfaces showed a significant increase with time, reaching a maximum at 21 days post-challenge and declined thereafter, irrespective of diet groups. Challenge with P. perurans influenced the mRNA expression of examined genes involved in immune and inflammatory response (TNF-α, iNOS, IL4-13b, GATA-3, IL-1β, p53, COX2 and PGE₂-EP4), but diet did not influence the gene expression. In conclusion, an increase in dietary n-6/n-3 FA ratio influenced the growth of Atlantic salmon challenged with P. perurans; however, it did not alter the mRNA expression of immune genes or progression of the disease.

Comparison of Three Feeding Regimens on Blood Fatty Acids Metabolites of Wujumqin Sheep in Inner Mongolia

Simple Summary

The traditional sheep feeding system in Inner Mongolia, based on pasture grazing, is gradually transforming into a semi-grazing plus supplementation or feedlot approach, as grassland ecological protection becomes increasingly important. The fatty acid composition of the animals’ tissues changes with transformation of the feeding system. However, the changes to blood fatty acid metabolites in sheep as a result of alterations to the feeding regimen are unknown. In this study, pasture feeding, pasture feeding plus corn supplementation, and barn feeding were carried out to explore the effects of feeding regimens on blood fatty acid composition and metabolic pathways of sheep using a metabolomic approach. The results revealed that compared to grazing, concentrate supplement feeding regimens, including either grazing plus supplements or feeding indoors, down-regulated blood n-3 PUFA biosynthesis and up-regulated blood inflammatory compound metabolism by n-6 PUFA. These data suggest that under different feeding regimens, an appropriate ratio of n-6/n-3 PUFA in ruminant diets will contribute to increasingly high-quality animal production and improved immunocompetence.

Abstract

Feeding regimens influence the fatty acid composition of animal-derived products. However, there is limited information on the effect of feeding regimens on the blood fatty acid composition and metabolic pathways of ruminant animals. In this study, 30 Wujumqin sheep were randomly assigned to three groups, PF (pasture feeding), PSF (pasture feeding plus corn supplementation) and BF (barn feeding), to examine the effects of feeding regimens on blood fatty acid composition and metabolic pathways through a metabolomic approach. The results showed that the BF sheep had increased serum n-6 polyunsaturated fatty acids levels, while the PF and PSF sheep had increased serum n-3 PUFA levels. Compared to the BF and PSF sheep that were fed ground corn, the PF sheep that only ate natural grass had up-regulated serum DHA levels. Meanwhile, blood metabolites from linoleic acid and arachidonic acid, including pro-inflammatory products (20-HETE, LTs, TX etc.) and anti-inflammatory products (LXB4, DHETs, HPETEs etc.) were elevated in the BF group. It was found that, compared to grazing, concentrate supplement feeding regimens, including either grazing plus supplements or feeding indoors, down-regulated blood n-3 PUFA biosynthesis and up-regulated the blood inflammatory compound metabolism by n-6 PUFA.

Influence of Dietary Long-Chain Polyunsaturated Fatty Acids and ω6 to ω3 Ratios on Head Kidney Lipid Composition and Expression of Fatty Acid and Eicosanoid Metabolism Genes in Atlantic Salmon (Salmo salar)

The interaction of dietary eicosapentaenoic acid and docosahexaenoic acid (EPA+DHA) levels with omega-6 to omega-3 ratios (ω6:ω3), and their impact on head kidney lipid metabolism in farmed fish, are not fully elucidated. We investigated the influence of five plant-based diets (12-week exposure) with varying EPA+DHA levels (0.3, 1.0, or 1.4%) and ω6:ω3 (high ω6, high ω3, or balanced) on tissue lipid composition, and transcript expression of genes involved in fatty acid and eicosanoid metabolism in Atlantic salmon head kidney. Tissue fatty acid composition was reflective of the diet with respect to C₁₈ PUFA and MUFA levels (% of total FA), and ω6:ω3 (0.5–1.5). Fish fed 0.3% EPA+DHA with high ω6 (0.3% EPA+DHA↑ω6) had the highest increase in proportions (1.7–2.3-fold) and in concentrations (1.4-1.8-fold) of arachidonic acid (ARA). EPA showed the greatest decrease in proportion and in concentration (by ~½) in the 0.3% EPA+DHA↑ω6 fed fish compared to the other treatments. However, no differences were observed in EPA proportions among salmon fed the high ω3 (0.3 and 1.0% EPA+DHA) and balanced (1.4% EPA+DHA) diets, and DHA proportions were similar among all treatments. Further, the transcript expression of elovl5a was lowest in the 0.3% EPA+DHA↑ω6 fed fish, and correlated positively with 20:3ω3, 20:4ω3 and EPA:ARA in the head kidney. This indicates that high dietary 18:3ω3 promoted the synthesis of ω3 LC-PUFA. Dietary EPA+DHA levels had a positive impact on elovl5a, fadsd5 and srebp1 expression, and these transcripts positively correlated with tissue ΣMUFA. This supported the hypothesis that LC-PUFA synthesis is positively influenced by tissue MUFA levels in Atlantic salmon. The expression of pparaa was higher in the 0.3% EPA+DHA↑ω6 compared to the 0.3% EPA+DHA↑ω3 fed fish. Finally, significant correlations between head kidney fatty acid composition and the expression of eicosanoid synthesis-related transcripts (i.e., 5loxa, 5loxb, cox1, cox2, ptges2, ptges3, and pgds) illustrated the constitutive relationships among fatty acids and eicosanoid metabolism in salmon.

Dietary ARA Improves COX Activity in Broodstock and Offspring Survival Fitness of a Model Organism (Medaka Oryzias latipes)

A 3-week feeding trial was conducted in medaka broodstock (age five months) to examine the effect of dietary arachidonic acid (ARA) level (range: 4-23 mg g^-1 of total fatty acids (TFAs)) on fertility, cyclooxygenase (COX) activity, egg size, sperm motility parameters, hatching rate and weight of hatch, survival and growth of larvae. After spawn induction and dietary exposure to 4 mg ARA g^-1 TFA, broodstock were fed a diet containing ARA in the amounts: 4 (continued, as control), 5, 14 and 23 mg g^-1 TFA. COX1 activity in the liver and the number of COX2-positive cells in the ovaries was increased in females fed the diets containing the two highest amounts of ARA. The highest sperm motility parameters were observed in males fed a diet containing 23 mg ARA g^-1 TFA. The hatchability rate and bodyweight of hatchlings were higher in the group obtained from broodstock fed a diet containing 23 mg ARA g^-1 TFA (79% and 0.66 mg fish^-1, respectively) compared with 4 mg ARA g^-1 TFA (50% and 0.40 mg fish^-1). The average mortality of offspring obtained from this group at 7 days post hatching was significantly higher than that of all other groups.

Effects of dietary arachidonic acid in European sea bass (Dicentrarchus labrax) distal intestine lipid classes and gut health

The use of low fishmeal/fish oil in marine fish diets affects dietary essential fatty acids (EFAs) composition and concentration and, subsequently, may produce a marginal deficiency of those fatty acids with a direct impact on the fish intestinal physiology. Supplementation of essential fatty acids is necessary to cover the requirements of the different EFAs, including the ones belonging to the n-6 series, such as arachidonic acid (ARA). ARA, besides its structural role in the configuration of the lipid classes of the intestine, plays an important role in the functionality of the gut-associated immune tissue (GALT). The present study aimed to test five levels of dietary ARA (ARA0.5 (0.5%), ARA1 (1%), ARA2 (2%), ARA4 (4%), and ARA6 (6%)) for European sea bass (Dicentrarchus labrax) juveniles in order to determine (a) its effect in selected distal intestine (DI) lipid classes composition and (b) how these changes affected gut bacterial translocation rates and selected GALT-related gene expression pre and post challenge. No differences were found between distal intestines of fish fed with the graded ARA levels in total neutral lipids and total polar lipids. However, DI of fish fed with the ARA6 diet presented a higher (P < 0.05) level of phosphatidylethanolamine (PE) and sphingomyelin (SM) than those DI of fish fed with the ARA0.5 diet. In general terms, fatty acid profiles of DI lipid classes mirrored those of the diet dietary. Nevertheless, selective retention of ARA could be observed in glycerophospholipids when dietary levels are low (diet ARA0.5), as reflected in the higher glycerophospholipids-ARA/dietary-ARA ratio for those animals. Increased ARA dietary supplementation was inversely correlated with eicosapentaenoic acid (EPA) content in lipid classes, when data from fish fed with the diets with the same basal composition (diets ARA1 to ARA6). ARA supplementation did not affect intestinal morphometry, goblet cell number, or fish survival, in terms of gut bacterial translocation, along the challenge test. However, after the experimental infection with Vibrio anguillarum, the relative expression of cox-2 and il-1β were upregulated (P < 0.05) in DI of fish fed with the diets ARA0.5 and ARA2 compared with fish fed with the rest of the experimental diets. Although dietary ARA did not affect fish survival, it altered the fatty acid composition of glycerophospholipids and the expression of pro-inflammatory genes after infection when included at the lowest concentration, which could be compromising the physical and the immune functionality of the DI, denoting the importance of ARA supplementation when low FO diets are used for marine fish.

Response of pearl oyster Pinctada fucata martensii to allograft-induced stress from lipid metabolism

The pearl oyster, Pinctada fucata martensii, produces high-quality pearls. During pearl production, excess immune and inflammatory response after transplantation will lead to nucleus rejection, pearl sac formation failure, and death of the host pearl oyster. The hemocyte transcriptome and fatty acid (FA) contents in the adductor muscle before and after transplantation were analyzed to investigate the response of pearl oyster P. f. martensii to allograft-induced stress from lipid metabolism. The hemocyte transcriptome analysis detected 193 lipid metabolism-related genes, such as the elongation of very long-chain FA protein 5, acyl-CoA 6-desaturase, cytochrome P450, phospholipase A2, glycerol-3-phosphate O-acyltransferase, and prostaglandin-H2 d-isomerase. Pathway enrichment analyses revealed that these genes were mainly involved in the "biosynthesis of unsaturated FAs," "FA biosynthesis," "ARA metabolism," and "glycerolipid metabolism." An analysis of FA contents in the adductor muscle indicated no significant difference in the contents of lauric acid, myristic acid, pentadecanoic acid, palmitic acid, palmitoleic acid, heptadecanoic acid, stearic acid, oleic acid, vaccenic acid, linoleic acid, arachidic acid, α-linolenic acid, eicosadienoic acid, docosadienoic acid, and 11,14,17-eicosatrienoic acid. However, ARA, DHA, and EPA in the adductor muscle after transplantation were significantly greater than those processed without grafting surgery. These results suggest that pearl oysters require more polyunsaturated FAs (PUFAs) to regulate their inflammatory and immune response after transplantation. However, their ability to biosynthesize unsaturated FAs is limited. Given these results, the addition of PUFA-containing diets or selection of a line with strong ability to biosynthesize unsaturated FAs may be valuable for pearl oyster recovery after transplantation.

Characterisation of Chinook salmon (Oncorhynchus tshawytscha) blood and validation of flow cytometry cell count and viability assay kit

New Zealand Chinook salmon (Oncorhynchus tshawytscha) industry has great potential for growth and expansion. While production is relatively free of health problems, there is limited literature on haematology, and immunological tools to safeguard against possible future health threats. The current study aim was to characterise New Zealand farmed O. tshawytscha peripheral blood cellular composition, develop a micro-volume method to isolate peripheral blood mononuclear cells (PBMCs) and validate a microcapillary flow cytometry assay kit for PBMC cell count and viability assessment. We used light microscopy to characterise peripheral blood and PBMC cellular composition in combination with a flow cytometer Sysmex XT 2000i Haematology Analyser. ImageJ version 1.52 was used for cell size characterisation of freshly stained blood. The stability of PBMCs stained with the Muse^® Cell Count and Viability Assay Kit and the Trypan blue assay stains were studied at 4 °C and 21 °C for 60 min; while the Muse^® Cell Count and Viability Assay Kit was validated against the Trypan blue assay haemocytometer chamber to assess PBMC count and viability. Findings showed that O. tshawytscha smolt yearlings had total blood cell counts in the range of 1.9-2.7 × 10⁶ μL^-1. Differential cell counts revealed five cell types, comprising 97.18% erythrocytes, 2.03% lymphocytes, 0.67% thrombocytes, 0.09% monocytes, and unquantifiable neutrophils. Using micro-volumes of blood and Lymphoprep™, we successfully isolated fish PBMCs. Significantly, stained PBMCs remained stable for up to 45 min at 4 °C and 21 °C; while validation of the Muse^® protocol showed that this microfluidic instrument delivered more accurate and precise viability results than the haemocytometer. The Muse^® protocol is rapid, easy to use, has quick calibration steps, and is suitable for field use to facilitate onsite sample processing. These findings pave the way for future assessments of fish health and in vitro immunological studies in O. tshawytscha.

Effect of plant-based diets with varying ratios of ω6 to ω3 fatty acids on growth performance, tissue composition, fatty acid biosynthesis and lipid-related gene expression in Atlantic salmon (Salmo salar)

Little is known about how variation in omega-6 to omega-3 (ω6:ω3) fatty acid (FA) ratios affects lipid metabolism and eicosanoid synthesis in salmon, and the potential underlying molecular mechanisms. The current study examined the impact of five plant-based diets (12-week exposure) with varying ω6:ω3 (0.3-2.7) on the growth, tissue lipid composition (muscle and liver), and hepatic transcript expression of lipid metabolism and eicosanoid synthesis-related genes in Atlantic salmon. Growth performance and organ indices were not affected by dietary ω6:ω3. The liver and muscle FA composition was highly reflective of the diet (ω6:ω3 of 0.2-0.8 and 0.3-1.9, respectively) and suggested elongation and desaturation of the ω3 and ω6 precursors 18:3ω3 and 18:2ω6. Furthermore, proportions of ω6 and ω3 PUFA in both tissues showed significant positive correlations with dietary inclusion (% of diet) of soy and linseed oils, respectively. Compound-specific stable isotope analysis (CSIA) further demonstrated that liver long-chain polyunsaturated fatty acid (LC-PUFA) synthesis (specifically 20:5ω3 and 20:4ω6) was largely driven by dietary 18:3ω3 and 18:2ω6, even when 20:5ω3 and 22:6ω3 were supplied at levels above minimum requirements. In addition, significant positive and negative correlations were identified between the transcript expression of LC-PUFA synthesis-related genes and liver ω6 and ω3 LC-PUFA, respectively, further supporting FA biosynthesis. Liver ω3 LC-PUFA also correlated negatively with the eicosanoid synthesis-related transcripts pgds and cox1. This is the first study to use CSIA, hepatic transcriptome, and tissue lipid composition analyses concurrently to demonstrate the impact of plant-based diets with varying ω6:ω3 on farmed Atlantic salmon.

Adipose tissue contributes to hepatic pro-inflammatory response when dietary fish oil is replaced by vegetable oil in large yellow croaker (Larimichthys crocea): An ex vivo study

The shortage of fish oil (FO) leads to the extensive use of vegetable oil (VO) in marine fish diets. High replacement percentage of dietary FO by VO induced pro-inflammatory response of adipose tissue (AT) and liver tissue (LT) in large yellow croaker (Larimichthys crocea). Mammalian studies showed that the secretion of cytokines by AT affected the immune response of LT. To investigate whether or not the inflammation response of LT is related to AT in large yellow croaker, LT and AT cells from fish fed FO diet (FOL and FOA) and VO diet (VOL and VOA) were co-cultured in a trans-well system, which resulted in an assembly of the two cells types sharing the culture medium but being separated by the membrane of the insert. Co-culture of FOL and FOA was selected as the control group (FOL-FOA). Results indicated that, when compared with the control group, the expression of pro-inflammatory genes (toll like receptors [TLRs], tumour necrosis factor α [TNFα], interleukin 1β [IL1β], suppressor of cytokine signalling 3 [SOCS3] and cyclooxygenase 2 [COX2]) in FOL was significantly increased in the co-culture group of FOL and VOA (FOL-VOA), while the expression of anti-inflammatory genes (arginase I [ArgI] and transforming growth factor β1 [TGFβ1]) in FOL was significantly depressed. On the contrary, a significantly depressed expression of pro-inflammatory genes (TLRs, TNFα, IL1β and COX2) and increased expression of anti-inflammatory genes (interleukin 10 [IL10]) in VOL was observed in the co-culture group of VOL and FOA (VOL-FOA) when compared with the co-culture group of VOL and VOA (VOL-VOA). The change of immune-related gene expressions in LT cells was attributed to nuclear factor κB (NF-κB) signalling since the expression of the p65 protein was observed to show a similar trend to the expression of pro-inflammatory genes. It is speculated that dietary VO increased the secretion of cytokines, which induced pro-inflammatory response in LT cells. These ex vivo results indicate that AT plays a vital role in LT pro-inflammatory response in fish fed VO diet.

Analysis of hepatic transcriptome demonstrates altered lipid metabolism following Lactobacillus johnsonii BS15 prevention in chickens with subclinical necrotic enteritis

Background

Subclinical necrotic enteritis (SNE) widely outbreaks in chickens which inflicted growth-slowing, causing enormous social and economic burdens. To better understand the molecular underpinnings of SNE on lipid metabolism and explore novel preventative strategies against SNE, we studied the regulatory mechanism of a potential probiotic, Lactobacillus johnsonii BS15 on the lipid metabolism pathways involved in chickens with SNE.

Methods

One hundred eighty one-day-old chickens were randomly divided into three groups and arranged with basal diet (control and SNE group). Added with BS15 (1 × 10⁶ cfu/g) or Man Rogosa Sharpe (MRS) liquid medium for 28 days. The hepatic gene expression of each group was then measured using high-throughput analysis methods (RNA-Seq). Quantitative real-time PCR (qRT-PCR) was used to detect the expression changes of the related genes.

Results

The results showed that there are eleven lipid metabolic pathways were found during the prevention of BS15 treatment in SNE chickens by RNA-Seq, including the peroxisome proliferator-activated receptor (PPAR) signaling pathway and arachidonic acid metabolism. BS15 notably facilitated the expressions of fatty acid binding protein 2 (FABP2), acyl-CoA synthetase bubblegum family member 1 (ACSBG1), perilipin 1 (PLIN1) and perilipin 2 (PLIN2), which were involved in PPAR signaling pathway of SNE chickens. Besides, suppression of phospholipase A2 group IVA (PLA2G4A) in arachidonic acid metabolism was observed in SNE chickens after BS15 prevention. The expression patterns of FABP2, ACSBG1, PLIN1, PLIN2 and PLA24G in qRT-PCR validation were consistent with RNA-Seq results.

Conclusions

These findings indicate that SNE may affect the hepatic lipid metabolism of chickens. Meanwhile, BS15 pretreatment may provide a prospective natural prophylaxis strategy against SNE through improving the PPAR signaling pathway and arachidonic acid metabolism.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0741-5) contains supplementary material, which is available to authorized users.

The impaired immune function and structural integrity by dietary iron deficiency or excess in gill of fish after infection with Flavobacterium columnare: Regulation of NF-κB, TOR, JNK, p38MAPK, Nrf2 and MLCK signalling

The aim of this study was to investigate the effects and potential mechanisms of dietary iron on immune function and structural integrity in gill of young grass carp (Ctenopharyngodon idella). A total of 630 grass carp (242.32 ± 0.58 g) were fed diets containing graded levels of iron at 12.15 (basal diet), 35.38, 63.47, 86.43, 111.09, 136.37 and 73.50 mg/kg for 60 days. Subsequently, a challenge test was conducted by infection with Flavobacterium columnare to investigate the effects of dietary iron on gill immune function and structural integrity in young grass carp. First, the results indicated that compared with the optimal iron level, iron deficiency decreased lysozyme (LZ) and acid phosphatase (ACP) activities, complement 3 (C3), C4 and immunoglobulin M (IgM) contents, and down-regulated the mRNA levels of antibacterial peptides, anti-inflammatory cytokines (except IL-4/13B), inhibitor of κBα (IκBα), target of rapamycin (TOR) and ribosomal protein S6 kinase 1 (S6K1). In contrast, iron deficiency up-regulated the mRNA levels of pro-inflammatory cytokines (except IL-6 and IFN-γ2), nuclear factor κB p65 (NF-κBp65), IκB kinases α (IKK), IKKβ, IKKγ, eIF4E-binding protein 1 (4E-BP1) and 4E-BP2 in gill of young grass carp, indicating that iron deficiency could impair immune function in fish gill. Second, iron deficiency down-regulated the mRNA levels of inhibitor of apoptosis protein (IAP) and myeloid cell leukemia 1 (Mcl-1), decreased activities and mRNA levels of antioxidant enzymes, down-regulated the mRNA levels of NF-E2-related factor 2 (Nrf2) and tight junction proteins (except claudin-12 and -15), and simultaneously increased malondialdehyde (MDA), protein carbonyl (PC) and reactive oxygen species (ROS) contents. Iron deficiency also up-regulated mRNA levels of cysteinyl aspartic acid-protease (caspase) -2, -7, -8, -9, Fas ligand (FasL), apoptotic protease activating factor-1 (Apaf-1), B-cell-lymphoma-2 associated X protein (Bax), p38 mitogen-activated protein kinase (p38MAPK), Kelch-like ECH-associating protein (Keap) 1a, Keap1b, claudin-12, -15 and MLCK, indicating that iron deficiency could disturb the structural integrity of gill in fish. Third, iron excess impaired immune function and structural integrity in gill of young grass carp. Forth, there was a better effect of ferrous fumarate than ferrous sulfate in young grass carp. Finally, the iron requirements based on ability against gill rot, ACP activity and MDA content in gill of young grass carp were estimated to be 76.52, 80.43 and 83.17 mg/kg, respectively.

Prostaglandins in teleost ovulation: A review of the roles with a view to comparison with prostaglandins in mammalian ovulation

Prostaglandins are well known to be central regulators of vertebrate ovulation. Studies addressing the role of prostaglandins in mammalian ovulation have established that they are involved in the processes of oocyte maturation and cumulus oocyte complex expansion. In contrast, despite the first indication of the role of prostaglandins in teleost ovulation appearing 40 years ago, the mechanistic background of their role has long been unknown. However, studies conducted on medaka over the past decade have provided valuable information. Emerging evidence indicates an indispensable role of prostaglandin E₂ and its receptor subtype Ptger4b in the process of follicle rupture. In this review, we summarize studies addressing the role of prostaglandins in teleost ovulation and describe recent advances. To help understand differences from and similarities to ovulation in mammalian species, the findings on the roles of prostaglandins in mammalian ovulation are discussed in parallel.

A comparative study: Difference in omega-6/omega-3 balance and saturated fat in diets for Atlantic salmon (Salmo salar) affect immune-, fat metabolism-, oxidative and apoptotic-gene expression, and eicosanoid secretion in head kidney leukocytes

The aim of this study was to compare how different dietary vegetable oil n-6/n-3 ratios affect gene responses involved in inflammation, signaling pathways, fatty acid synthesis and oxidation, oxidation and apoptosis as well as eicosanoid production in salmon head kidney tissues and isolated head kidney leukocytes. Salmon smolts (200 g) were fed four different diets where the main lipid components were palm oil (n-6/n-3 ratio = 0.7), rapeseed oil (n-6/n-3 ratio = 0.9), and soybean oil (n-6/n-3 ratio = 2.4) and a high soybean oil diet with an n-6/n-3 ratio = 4. Both head kidney tissue and leukocytes isolated from head kidneys were sampled from the four diets, but from different fish. Leukocytes isolated from the head kidneys were seeded into culture wells and added lipopolysaccharide (LPS) to induce inflammatory responses. Controls without LPS were included. Head kidney leukocytes and the tissues should have the same phenotype reflecting the different diets. Interleukin 1β (IL-1β) transcription was elevated in head kidney tissue and especially in LPS treated leukocytes isolated from soybean oil (n-6/n-3 = 2.4) fed salmon, which confirmed the suitability of the in vitro model in this experiment. Leukocytes, treated with LPS, and isolated from salmon fed the soybean oil diet (n-6/n-3 = 2.4) also upregulated tumor necrosis factor alpha (tnf-α), cyclooxygenase (cox2), prostaglandin D and E synthase (ptgds, ptges), fatty acyl synthase (fas), 5 and 6 desaturases (5des, 6 des) and a fatty acid translocase protein (cd36) when compared to the other diets. The results suggest that diets with a specific n-6/n-3 ratio influence the transcription of pro-inflammatory genes and may be cross-linked to transcription of selected fatty acid metabolism genes. Salmon fed the palm oil diet (n-6/n-3 = 0.7) showed a lower expression of inflammatory genes. Instead, peroxisome proliferator activated receptor β1 (pparβ1), acyl coenzyme A (aco), apoptosis regulator (bax) and superoxide dismutase (sod) were upregulated in leukocytes in vitro, while head kidney tissue transcription of a dendritic marker (cd83) was lower than measured in tissues from fish fed the other diets. The concentration of LTB4 (10-20 ng/mL) were relatively constant in leukocyte supernatants, all diets. Head kidney leukocytes from soybean oil (n-6/n-3 = 2.4) fed fish produced LPS induced PGE2 (mean 0.5 ng/mL) while leukocytes isolated from palm oil diet (n-6/n-3 = 0.7) secreted very high amounts of LTB5 (50-70 ng/mL). In addition, equal amounts of LPS induced PGE2 and PGE3 (mean 0, 5 ng/mL) were produced, indicating that the n-6/n-3 ratio of this saturated fatty acid may have a specific impact on eicosanoid production in the head kidney of salmon.

Comparative analysis of effects of dietary arachidonic acid and EPA on growth, tissue fatty acid composition, antioxidant response and lipid metabolism in juvenile grass carp, Ctenopharyngodon idellus

Four isonitrogenous and isoenergetic purified diets containing free arachidonic acid (ARA) or EPA (control group), 0·30 % ARA, 0·30 % EPA and 0·30 % ARA+EPA (equivalent) were designed to feed juvenile grass carp (10·21 (sd 0·10) g) for 10 weeks. Only the EPA group presented better growth performance compared with the control group (P<0·05). Dietary ARA and EPA were incorporated into polar lipids more than non-polar lipids in hepatopancreas but not intraperitoneal fat (IPF) tissue. Fish fed ARA and EPA showed an increase of serum superoxide dismutase and catalase activities, and decrease of glutathione peroxidase activity and malondialdehyde contents (P<0·05). The hepatopancreatic TAG levels decreased both in ARA and EPA groups (P<0·05), accompanied by the decrease of lipoprotein lipase (LPL) activity in the ARA group (P<0·05). Fatty acid synthase (FAS), diacylglycerol O-acyltransferase and apoE gene expression in the hepatopancreas decreased in fish fed ARA and EPA, but only the ARA group exhibited increased mRNA level of adipose TAG lipase (ATGL) (P<0·05). Decreased IPF index and adipocyte sizes were found in the ARA group (P<0·05). Meanwhile, the ARA group showed decreased expression levels of adipogenic genes CCAAT enhancer-binding protein α, LPL and FAS, and increased levels of the lipid catabolic genes PPARα, ATGL, hormone-sensitive lipase and carnitine palmitoyltransferase 1 (CPT-1) in IPF, whereas the EPA group only increased PPARα and CPT-1 mRNA expression and showed less levels than the ARA group. Overall, dietary EPA is beneficial to the growth performance, whereas ARA is more potent in inducing lipolysis and inhibiting adipogenesis, especially in IPF. Meanwhile, dietary ARA and EPA showed the similar preference in esterification and the improvement in antioxidant response.

Dietary arachidonic acid affects immune function and fatty acid composition in cultured rabbitfish Siganus rivulatus

The marbled spinefoot rabbitfish (Siganus rivulatus) is an economically valuable fish species that has potential for commercial production in aquaculture. To overcome challenges in its sustainable production, a formulated diet is required for imparting health and robustness. This study evaluates the effect of dietary supplementation with arachidonic acid (ARA; 20:4n-6) on growth, survival, immune function and fatty acid composition of red blood cells (RBCs) in rabbitfish. We conducted two feeding trials using juvenile fish (to evaluate growth and survival) and adults (to evaluate immune function and fatty acid incorporation). Fish were fed diets supplemented with three different levels of ARA (in % of total fatty acids): 0.6 (unsupplemented control), 2.6 (moderate) and 4.7 (high). The fish fed with moderate ARA levels exhibited improved (p < 0.05) growth over the control and the high ARA level groups. During an outbreak of Streptococcus iniae, fish fed with moderate ARA survived significantly (p < 0.05) better (89%) than the control and the high ARA groups (59% and 48%, respectively). Moderate ARA supplementation resulted in elevated lysozyme and complement levels in the plasma of rabbitfish. A significant increase in the total serum immunoglobulin levels was observed in both the medium and the high ARA level groups; however, a decrease in antiprotease activity was recorded in the supplemented groups as compared to the control. Fatty acid analysis in fish red blood cells revealed a significant (p < 0.05) increase in the proportion of ARA of total fatty acids in the groups fed with the medium and the high ARA level diets (9.5% and 11.2%, respectively, compared to 7.1% in the control). Concomitantly, there was a decrease in the proportion of eicosapentaenoic acid (EPA; 20:5n-3), dihomo-γ linolenic acid (DGLA; 20:3n-6) and several 18-carbon unsaturated fatty acids in these groups. In conclusion, ARA in rabbitfish feeds improved growth, survival as well as innate and acquired humoral immune functions. Thus ARA supplementation in the diet of this species could be a valuable step towards establishing the commercial culture of rabbitfish.

Role of cyclooxygenase-mediated metabolites in lipid metabolism and expression of some immune-related genes in juvenile grass carp (Ctenopharyngodon idellus) fed arachidonic acid

Cyclooxygenase (COX) catalyzes the conversion of arachidonic acid (ARA) to prostaglandins, and COX-mediated metabolites play important roles in the regulation of lipid metabolism and immunity in mammals. However, such roles of COX in fish remain largely unknown. In this study, we designed three semi-purified diets, namely ARA-free (control), ARA, and ARA + acetylsalicylic acid (ASA; a COX inhibitor), and used them to feed grass carp (27.65 ± 3.05 g) for 8 weeks. The results showed that dietary ARA significantly increased the amount of ARA in the hepatopancreas, muscle, and kidney (P < 0.05), whereas this increase was reduced by dietary ASA. The hepatopancreatic prostaglandin E₂ content increased in the ARA group, and this increase was inhibited by ASA (P < 0.05). ARA decreased the lipid content in the hepatopancreas, whereas ASA recovered lipid content to a significant level (P < 0.05). ARA significantly decreased the messenger RNA (mRNA) expression levels of fatty acid synthase and stearoyl-CoA desaturase in the hepatopancreas (P < 0.05). However, ASA did not rescue the mRNA expression of these genes (P > 0.05). Interestingly, ARA significantly enhanced the level of peroxisome proliferator-activated receptor α gene expression, and this increase was attenuated by ASA (P < 0.05). Finally, ARA significantly enhanced the mRNA expression of myeloid differentiation factor 88 (MyD88) in the kidney, and ASA attenuated the expression of toll-like receptor 22 and MyD88 (P < 0.05). In conclusion, our findings suggest that COX metabolites play important roles in the inhibition of lipid accumulation in the hepatopancreas of grass carp fed with ARA and that regulation of gene expression promotes lipid catabolism rather than lipogenic activities. Additionally, these eicosanoids might participate in the upregulation of immunity-related genes in the kidney.

Supplementation of arachidonic acid rich oil in European sea bass juveniles (Dicentrarchus labrax) diets: Effects on leucocytes and plasma fatty acid profiles, selected immune parameters and circulating prostaglandins levels

The main objective of this study was to assess the effects of graded levels of dietary arachidonic acid (ARA), supplemented from alternative sources, on fatty acid composition of plasma and head kidney leucocytes of European sea bass (Dicentrarchus labrax). For that purpose, sea bass juveniles were fed four diets containing graded levels of ARA as follows: 0.5% (ARA0.5), 1% (ARA1), 2% (ARA2) and 4% (ARA4) during 60 days. At the end of the feeding trial fatty acid profiles of plasma and head kidney leucocytes were analyzed. Besides, plasma prostaglandins levels, head kidney leucocytes respiratory burst activity; peroxidase activity and phagocytic index were assayed. Reducing dietary ARA levels below 1% markedly reduced European sea bass growth performance. However, fish fed diet ARA0.5 tried to compensate this dietary ARA deficiency by a selective deposition of ARA on plasma and head kidney leucocytes, reaching similar levels to those fish fed diet ARA1 after 60 days of feeding. Nevertheless, head kidney phagocytic capacity was reduced as dietary ARA content in relation not only to variations on membrane composition but also to changes on fish basal prostaglandins levels. Results obtained demonstrated the importance to supply the necessary quantity n-6 LC-PUFA, and not only n-3 LC-PUFA levels, in European sea bass diets, in relation to not only growth performance but also immune system function.

Dietary resveratrol improves immunity but reduces reproduction of broodstock medaka Oryzias latipes (Temminck & Schlegel)

Here, we investigated the effect of dietary resveratrol (20, 40, and 80 µg/g BW/day) on cell-mediated immunity (activity of spleen phagocytes and proliferative response of lymphocytes) and reproductive parameters (egg and sperm quality, i.e. fecundity-total number of eggs produced by individual fish, fertility, embryo survival, and hatching rate) in medaka. Fish fed feed with resveratrol at 40 and 80 µg/g BW/day had significantly higher metabolic activity and intracellular phagocyte killing activity than control. The proliferative lymphocyte activity of the fish from R80 group was greater by more than 20 % in comparison with the control group (P < 0.05). The percentage of macrophages (MO) and their mean fluorescence intensities (MFI) in R40 and R80 groups were significantly higher compared to C and R20 groups (P < 0.05). The differences in MO and MFI values ranged from 52.5 % (±1.5; R0 group) to 65.8 % (±1.6; R80 group) and from 23.2 (±1.4; R0 group) to 38.2 (±2.4; R80 group), respectively. Moreover, resveratrol at 80 µg/g BW/day decreased liver COX activity, i.e. 5.4 in R80 group and 7.9 in R0 group (P < 0.05). The motility parameters of the sperm obtained from the males fed feed supplemented with resveratrol at 80 µg/g BW/day exhibited the highest values except the linearity, which was lower as compared to the control (P < 0.05). The results indicate that diet supplemented with resveratrol at a dosage of 40 µg/g BW/day improves phagocyte killing ability and lymphocyte proliferation in broodstock and accelerates offspring hatch. Also, the results suggest that COX activity influences sperm and oocyte quality in fish; the presence of a COX inhibitor in the dose of 40 µg/g BW/day decreased the embryo survival.

Vitamin A and arachidonic acid altered the skeletal mineralization in Atlantic cod (Gadus morhua) larvae without any interactions on the transcriptional level

The main object of this study was to evaluate the impact of different levels of vitamin A (VA) and arachidonic acid (ARA) in relation to eicosapentaenoic acid (EPA) on mineralization and gene expression in Atlantic cod larvae (Gadus morhua). First-feeding larvae were fed enriched rotifers from start-feeding until 29 days post hatch (dph). Larvae in four tanks were fed one of the following diets: control (EPA/ARA ratio: 15.8, 0.9μg VA g(-1)), control+VA (EPA/ARA ratio: 15.8, 7.8μg VA g(-1)), High ARA (EPA/ARA ratio: 0.9, 1.5μg VA g(-1)) or High ARA+VA (EPA/ARA ratio: 0.9, 12.0μg VA g(-1)). Larvae fed High ARA+VA were shorter at 29dph compared to the other groups and had significantly less mineralized bones when comparing larvae of similar size, showing interaction effects between VA and ARA. Although transcriptomic analysis did not reveal any interaction effects, a higher number of genes were differentially expressed in the high ARA fed larvae compared to control+VA fed larvae. Furthermore, bglap1, bglap2 and col10a1 were all down-regulated in larvae fed High ARA-diets and to a greater extent than larvae fed VA supplemented diet, indicating an additive effect on mineralization. In conclusion, this study showed that the dietary increase in ARA and VA altered the skeletal metabolism during larval development, most likely through signaling pathways specific for each nutrient rather than an interaction. The present study also demonstrates that VA could affect the larval response to ARA, even within the accepted non-toxic/non-deficient range.

Stress during slaughter increases lipid metabolites and decreases oxidative stability of farmed rainbow trout (Oncorhynchus mykiss) during frozen storage

The consequences of slaughter on the formation of lipid metabolites and oxidative stability of fish muscle during long term frozen storage (-10 °C) were evaluated using farmed rainbow trout killed by asphyxia in air or percussion. The level of major adenine nucleotides and their related compounds was determined in order to check the stress level during slaughter. Plasma lipid metabolites were studied through the determination of eicosanoids and docosanoids such as prostaglandins, leukotrienes, thromboxanes, isoprostanes, resolvins, hydroxides, hydroperoxides, coming from eicosapentaenoic (EPA), arachidonic (ARA), and docosahexaenoic (DHA) acids. In addition, lipid oxidative stability of fillets was monitored. Results revealed that stress during slaughter can greatly influence oxidative stress and oxidative stability of rainbow trout fillets. In fact, asphyxia, which was the most stressful, induced a higher production of some lipid mediators such as hydroperoxides and EPA-derived prostaglandins, such as 12-HpHEPE/15-HpHEPE and PGD3/PGE3. As a consequence, fillets derived from asphyxiated fish were less stable in terms of oxidative stability and showed lower shelf-life.

Evaluation of the impact of camelina oil-containing diets on the expression of genes involved in the innate anti-viral immune response in Atlantic cod (Gadus morhua)

To improve sustainability of aquaculture, especially for carnivorous species like Atlantic cod, replacement of fish oil-based diets with vegetable oil-based diets has been studied. The use of vegetable oil in fish feeds can significantly change the fatty acid composition of fish tissues, and given the importance of fatty acids in inflammation and immunity, this change could potentially impact the immune response and health of the fish. The oilseed Camelina sativa is a promising source for this vegetable oil, because of the high oil content of its seeds (40%), a higher n-3 fatty acid content than most other oilseeds, and a high amount of γ-tocopherol. This study aims to investigate the effect of the replacement of dietary fish oil with oil from Camelina sativa on the immune response of Atlantic cod, as measured by the gene expression in spleen. Juvenile cod were fed on a fish oil-based diet (FO) or one of two diets in which camelina oil replaced 40% or 80% of fish oil (40CO and 80CO respectively) for 67 days, after which they were injected with either the viral mimic polyriboinosinic polyribocytidylic acid (pIC), or phosphate-buffered saline (PBS) as a control. Microarray analysis was used to determine the effect of the diet on the basal spleen transcriptome (pre-injection), and on the response to pIC (24 h post-injection). No marked differences in the spleen transcriptome were found between the three diets, either before or after injection with pIC. All fish, regardless of diet, showed a strong anti-viral response 24 h after pIC injection, with more than 500 genes having a significant difference of expression of 2-fold or higher compared to the PBS-injected fish for the FO, 40CO and 80CO diets. Gene Ontology annotation analysis of the three pIC-responsive gene lists indicated they were highly similar, and that the term 'immune system process' was significantly enriched in the pIC-responsive gene lists for all three diets. QPCR analysis for 5 genes with a known function in the anti-viral innate immune response (LGP2, STAT1, IRF1, ISG15 and viperin) showed modestly (smaller than 2-fold) up-regulated basal expression of LGP2, IRF1 and STAT1 in fish fed 40CO compared to the other diets. After pIC injection, all 5 genes were significantly and strongly up-regulated in pIC-injected fish compared to PBS-injected fish, but no significant differences were found between any of the diets. In conclusion, replacement of up to 80% of fish oil with camelina oil in Atlantic cod diets does not have a strong effect on basal spleen gene expression. Atlantic cod fed on camelina oil-containing diets are capable of mounting a strong anti-viral immune response, which is comparable to that in cod fed with a fish oil diet.

GC/MS-based metabolomics approach to identify biomarkers differentiating survivals from death in crucian carps infected by Edwardsiella tarda

Microbial disease problems constitute the largest single cause of economic losses in aquaculture. An understanding of immune system in aquaculture animals how to function in defense against bacterial infections is especially important to control these diseases and improve food quality and safety. In the present study, we use a crucian carp model to explore which pathways and metabolites are crucial for the defense against infection caused by Edwardsiella tarda EIB202. We establish the metabolic profile of crucian carps and then compare the metabolic difference between survivals and dead fish by self-control. We identify elevating unsaturated fatty acid biosynthesis and decreasing fructose and mannose metabolism as the most key pathways and increasing palmitic acid and decreasing d-mannose as the most crucial metabolites differentiating survivals from death in these fish infected by E. tarda. Our findings highlight the importance of metabolic strategy against bacterial infections.