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

Polyethylene microplastics impair chicken growth through gut microbiota-induced hepatic fatty acid metabolism dysfunction

Microplastics (MPs) negatively impact various terrestrial animals, but their comprehensive effects on Gallus gallus domesticus, key agricultural and ecological species connecting people and the environment, are not well-documented. This study investigates the effects of polyethylene (PE) MPs and phthalate esters (PAEs) on chicken growth, liver metabolism, and gut microbiota using multi-omics and 16S rRNA sequencing technology. Results show that PE MPs, particularly those containing PAEs, significantly reduced body weight gain and hepatic triglyceride levels by up to 71.2 % and 50.1 %, respectively (p < 0.05). The clean MPs affected energy metabolism, while PAE-spiked MPs disrupted fatty acid metabolism and triggered immune and inflammatory responses in the liver. Key genes related to fatty acid metabolism such as FAN, SCD and ELOVL5 were significantly downregulated, leading to imbalances in lipid metabolism. These disruptions in PAE-spiked MPs exposure were associated with the altered gut microbiota balance, including increased Firmicutes/Bacteroidetes ratios and changes in Actinobacteriota and Proteobacteria abundance. Totally, the study highlights a "Trojan Horse" effect, where MPs act as carriers for PAEs, intensifying toxicity through gut-liver axis interactions. The findings emphasize the role of gut microbiota in mediating liver dysfunction and impaired growth.

Microencapsulates of Moringa oleifera seed extracts enhance immunological parameters of Almaco jack (Seriola rivoliana) upon Aeromonas hydrophila challenge

Moringa oleifera seed (MoS) and spray-dried seed (Sd-Mo) were supplemented in experimental diets to Almaco Jack Seriola rivoliana, and sampled on weeks 2 and 4; also, resistance against Aeromonas hydrophila was evaluated. Chemical compounds were determined by GC/MS and polyphenols contents were determined in MoS. After 4 weeks of experimental trial, weight growth and bactericidal activity were evaluated in serum, while intestine content was obtained to determinate the short-chain fatty acids (SCFAs). Furthermore, remaining fish were challenged during week 4 against A. hydrophila, and immune response parameters were determined in serum; on the final day, fish were sampled to obtain leukocytes from head-kidney to evaluate innate immune parameters. The GC-MS analysis indicated that MoS contained 39 chemical compounds such as polyalcohol, in addition to the presence of phenols. The results revealed that Sd-Mo significantly increased (P < 0.05) weight gain after 2 and 4 weeks. Experimental diets supplemented with Sd-Mo showed significant increase on bactericidal activity against A. hydrophila A-315, as well as concentration of acetic (C2:0) acid obtained by SCFA in serum in this group of fish. After infection, total protein, lysozyme, nitric oxide and the antioxidant enzymes (SOD and CAT) were increased in serum from fish fed with Sd-Mo. Interestingly, ex vivo assay determined in head-kidney leukocytes revealed that fish fed with Sd-Mo increased their defense against A. hydrophila infection with enhanced phagocytosis, respiratory burst, myeloperoxidase, and nitric oxide production activities. In summary, this study suggested that fish fed with supplemented diets Sd-Mo (0.5 %) has a positive effect than not processed MoS, enhancing weight gain and in vivo and ex vivo immunological parameters after infection with A. hydrophila.

Insights into the Regulatory Role of MicroRNAs in Penaeus monodon Under Moderately Low Salinity Stress

MicroRNAs (miRNAs) play crucial roles in regulating various biological processes in crustaceans, including stress responses. Under acute low salinity stress conditions, miRNAs exhibit dynamic expression patterns that significantly influence the physiological and molecular responses of the shrimp. However, research on miRNAs in P. monodon is very limited, and their functions under low salinity stress remain unclear. In this study, by using high-throughput sequencing technology, we identified miRNAs and investigated their regulatory mechanism in P. monodon under low salinity stress. A total of 118 miRNAs were differentially expressed after low salinity exposure. These miRNAs were found to target genes involved in metabolism, pathogen infection, immune response and stress signaling pathways. By modulating the expression of these target genes, miRNAs were able to fine-tune the stress response of P. monodon, thereby enhancing its tolerance to low salinity. This study provides new insights into the regulatory roles of miRNAs in the stress response of aquatic organisms and suggests potential targets for genetic improvement to enhance stress tolerance in P. monodon aquaculture.

Evaluation of the Optimum Dietary Arachidonic Acid Level and Its Essentiality for Black Seabream (Acanthopagrus schlegelii): Based on Growth and Lipid Metabolism

The aim of this study was to investigate how dietary arachidonic acid (ARA) level affects growth performance and lipid metabolism in juvenile black seabream (Acanthopagrus schlegelii). A feeding trial was conducted for 8 weeks, during which the fish (0.99 ± 0.10 g) were fed six isonitrogenous and isolipidic diets with varying ARA levels of 0.1%, 0.59%, 1.04%, 1.42%, 1.94%, and 2.42%. Fish fed the diet with 1.42% ARA had significantly higher weight gain (WG) and specific growth rate (SGR) than the other groups (p < 0.05), except for the ARA1.04. As the ARA level increased, the liver and muscle effectively accumulated n-6 polyunsaturated fatty acids (n-6 PUFAs; p < 0.05). However, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and n-3 PUFA contents of liver and muscle significantly decreased by increasing dietary ARA level (p < 0.05). Results of liver histology showed dramatically increased vacuolar fat droplets leading to hepatic fat pathological changes in fish fed diets with ARA levels of 1.94% and 2.42% (p < 0.05). Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities increased with increasing dietary ARA level which was accompanied with elevated liver lipid content (p < 0.05). Consistently, triglyceride (TG) and nonesterified fatty acid (NEFA) concentrations of serum and liver, and serum cholesterol (CHO) concentration increased (p < 0.05). As the level of dietary ARA increased, the indicators of lipid metabolism such as sirtuin 1 (sirt1) and peroxisome proliferator-activated receptor α (pparα) also increased (p < 0.05). However, after reaching their peak in ARA1.04 group, the level of these indicators declined (p < 0.05). The same trend was observed for the expression of genes related to the downstream pathways. While the mRNA levels of sterol regulatory element-binding protein-1 (srebp-1) and its downstream genes were markedly increased with the increase of dietary ARA level (p < 0.05). In conclusion, these data suggested that the optimum dietary ARA requirement of A. schlegelii is 1.03% of diet based on the WG. The study revealed that a diet containing 1.04% ARA can activate the expression levels of sirt1 and pparα leading to promoted lipolysis. However, dietary ARA levels of ≥1.42% induced lipid accumulation in the liver, as they suppressed the mRNA levels of sirt1 and pparα, while elevating the expression level of genes related to lipogenesis.

Dietary ARA, DHA, and Carbohydrate Ratios Affect the Immune Status of Gilthead Sea Bream Juveniles upon Bacterial Challenge

This study aims to assess the effects of different dietary n-6/n-3 long-chain polyunsaturated fatty acid ratios and CHO content in the immune response of gilthead seabream. For that purpose, gilthead sea bream juveniles (initial body weight = 47.5 g) were fed for 84 days with four isoproteic (47% crude protein) and isolipidic (18% crude lipids) diets with high (20%) or low (5%) level of gelatinized starch (HS or LS diets, respectively) and included approximately 2.4% ARA or DHA. At the end of the trial, the DHA-enriched groups presented increased red blood cell (RBC) count, hemoglobin, plasmatic nitric oxide (NO) content, and antiprotease and alternative complement activities. The ARA groups had increased thrombocyte count, and plasmatic bactericidal activity against Vibrio anguillarum was lower in the fish fed the ARA/LS diet. After the feeding trial, the fish were challenged with an intraperitoneal injection (i.p.) of killed Photobacterium damselae subsp. piscicida (Phdp) and sampled at 4 and 24 h after the challenge. At 4 h after i.p., the ARA groups presented increased plasma total immunoglobulins (Ig) and bactericidal activity against V. anguillarum. In addition, the fish fed the ARA/LS diet presented lower white blood cell (WBC) and alternative complement activity. At 24 h after i.p., the ARA groups presented increased RBC, WBC, and thrombocyte numbers, total IG, plasma peroxidase activity, and casp3 expression in the distal intestine. The HS groups presented increased plasma NO content and bactericidal activity against Phdp and decreased protease, antiprotease activity, and bactericidal activity against V. anguillarum. In conclusion, high dietary DHA levels seemed to improve the immune status of unchallenged gilthead sea bream juveniles, while high dietary ARA levels improved the fish immune response to a bacterial challenge. The energy provided by dietary starch seems to be important to promote a fast response by the fish immune system after a challenge.

Enhancing Reproductive Performance of Freshwater Finfish Species through Dietary Lipids

Dietary lipid manipulation in the feed of commercially cultured finfish is used not only to improve production and culture but also to enhance their reproductive performances. The inclusion of lipid in broodstock diet positively affects growth, immunological responses, gonadogenesis, and larval survival. In this review, existing literature on the importance of freshwater finfish species to aquaculture and the inclusion of dietary lipid compounds in freshwater fish feed to accelerate the reproduction rate is being summarized and discussed. Although lipid compounds have been confirmed to improve reproductive performance, only a few members of the most economically important species have reaped benefits from quantitative and qualitative lipid studies. There is a knowledge gap on the effective inclusion and utilization of dietary lipids on gonad maturation, fecundity, fertilization, egg morphology, hatching rate, and consequently, larval quality contributing to the survival and good performance of freshwater fish culture. This review provides a baseline for potential future research for optimizing dietary lipid inclusion in freshwater broodstock diets.

Poplar bark lipids enhance mouse immunity by inducing T cell proliferation and differentiation

Research on the composition and application of immune enhancers in livestock and poultry breeding has been gaining interest in recent years. Poplar bark lipids (PBLs), which are extracted from poplar tree bark, are natural substances known to efficiently enhance the immune response. To understand the chemical makeup of PBLs and their underlying mechanism for enhancing the immune system, we extracted PBLs from poplar bark using petroleum ether and subjected these extracts to chemical analysis. To evaluate PBLs effect on the immune system mice were treated with different doses of PBL via gavage and sacrificed 4 weeks later. PBLs were shown to be rich in vitamin E, unsaturated fatty acids, and other immune-potentiating compounds. Treatment with PBLs increased the spleen index and stimulated spleen and thymus development. In addition, PBLs increased the number of CD3+CD4+ cells in the peripheral blood and the ratio of CD4+/CD8+ cells while decreasing the number of CD3+CD8+ cells. Moreover, PBLs significantly increased IL-4 and IFN-γ levels in mouse serum and TLR4 mRNA and protein expression in the spleen. Taken together these results demonstrate that PBLs exert their immune-potentiating effects by promoting spleen and thymus development, T lymphocyte proliferation and differentiation, and immune factor expression. These immune-potentiating effects may be related to the activation of TLR4. This study provides a theoretical basis for the development of PBLs as an immune adjuvant or feed additive in the future.

Dietary Supplementation with Omega-6 LC-PUFA-Rich Microalgae Regulates Mucosal Immune Response and Promotes Microbial Diversity in the Zebrafish Gut

The effect of dietary omega-6 long-chain polyunsaturated fatty acid (LC-PUFA) on host microbiome and gut associated immune function in fish is unexplored. The effect of dietary supplementation with the omega-6 LC-PUFA-rich microalga Lobosphaera incisa wild type (WT) and its delta-5 desaturase mutant (MUT), rich in arachidonic-acid and dihomo-gamma-linolenic acid (DGLA), respectively, on intestinal gene expression and microbial diversity was analyzed in zebrafish. For 1 month, fish were fed diets supplemented with broken biomass at 7.5% and 15% (w/w) of the two L. incisa strains and a control nonsupplemented commercial diet. Dietary supplementation resulted in elevated expression of genes related to arachidonic acid metabolism-cyclooxygenase 2 (cox-2), lipoxygenase 1(lox-1), anti-inflammatory cytokine-interleukin 10 (il-10), immune defense-lysozyme (lys), intestinal alkaline phosphatase (iap), complement (c3b), and antioxidants-catalase (cat), glutathione peroxidase (gpx). Microbiome analysis of the gut showed higher diversity indices for microbial communities in fish that were fed the supplemented diets compared to controls. Different treatment groups shared 237 operational taxonomic units (OTUs) that corresponded to the core microbiome, and unique OTUs were evident in different dietary groups. Overall, the zebrafish gut microbiome was dominated by the phylum Fusobacteria and Proteobacteria (averaging 38.4% and 34.6%, respectively), followed by Bacteroidetes (12.9%), Tenericutes, Planctomycetes, and Actinobacteria (at 3.1–1.3%). Significant interaction between some of the immune-related genes and microbial community was demonstrated.

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.

Antiviral activity of palmitic acid via autophagic flux inhibition in zebrafish (Danio rerio)

Fatty acids (FAs) are key elements that affect not only growth but also different immune functions, and therefore, nutrition is important for growing healthy fish. Zebrafish (Danio rerio) is a good model for assessing the beneficial effects of immunostimulants, including FAs, before applying them in aquaculture. Accordingly, this study evaluated the effects of palmitic acid (PA) treatment on different immune parameters of zebrafish and on the mortality caused by the spring viremia of carp virus (SVCV). The results suggest that PA modulates the infection outcome in vivo, which benefits zebrafish and results in reduced mortality and viral titres. The antiviral protection elicited by this FA seems to be associated with the inhibition of autophagy and is independent of other immune processes, such as neutrophil proliferation or type I interferon (IFN) activity. The use of PA as an immunostimulant at low concentrations showed great potential in the prevention of SVCV infections; therefore, this FA could help to prevent the mortality and morbidity caused by viral agents in aquacultured fish. Nevertheless, the potentially detrimental effects of suppressing autophagy in the organism should be taken into account.

Dietary Approaches to Attain Fish Health with Special Reference to their Immune System

Fish despite their low collocation in the vertebrate phylum possess a complete immune system. In teleost fish both innate and adaptive immune responses have been described with melanomacrophage centers (MMCs) equivalent to mammalian germinal centers. Primary lymphoid organs are represented by the thymus and kidney, while spleen and mucosa-associated lymphoid tissues act as secondary lymphoid organs. Functions of either innate immune cells (e.g., macrophages and dendritic cells) or adaptive immune cells (T and B lymphocytes) will be described in detail, even including their products, such as cytokines and antibodies. In spite of a robust immune arsenal, fish are very much exposed to infectious agents (marine bacteria, parasites, fungi, and viruses) and, consequentially, mortality is very much enhanced especially in farmed fish. In fact, in aquaculture stressful events (overcrowding), microbial infections very frequently lead to a high rate of mortality. With the aim to reduce mortality of farmed fish through the reinforcement of their immune status the current trend is to administer natural products together with the conventional feed. Then, in the second part of the present review emphasis will be placed on a series of products, such as prebiotics, probiotics and synbiotics, β-glucans, vitamins, fatty acids and polyphenols all used to feed farmed fish. With special reference to polyphenols, results of our group using red grape extracts to feed farmed European sea bass will be illustrated. In particular, determination of cytokine production at intestinal and splenic levels, areas of MMCs and development of hepatopancreas will represent the main biomarkers considered. All together, our own data and those of current literature suggests that natural product administration to farmed fish for their beneficial effects may, in part, solve the problem of fish mortality in aquaculture, enhancing their immune responses.

PPARα activation enhances the ability of nile tilapia (Oreochromis niloticus) to resist Aeromonas hydrophila infection

Peroxisome proliferator-activated receptor α (PPARα) plays critical physiological roles in energy metabolism, antioxidation and immunity of mammals, however, these functions have not been fully understood in fish. In the present study, Nile tilapia (Oreochromis niloticus) were fed with fenofibrate, an agonist of PPARα, for six weeks, and subsequently challenged with Aeromonas hydrophila. The results showed that PPARα was efficiently activated by fenofibrate through increasing mRNA and protein expressions and protein dephosphorylation. PPARα activation increased significantly mitochondrial fatty acid β-oxidation efficiency, the copy number of mitochondrial DNA and expression of monoamine oxidase (MAO), a marker gene of mitochondria. Meanwhile, PPARα activation also increased significantly the expression of NADH dehydrogenase [ubiquinone] 1α subcomplex subunit 9 (NDUFA9, complex I) and mitochondrial cytochrome c oxidase 1 (MTCO1, complex IV). The fenofibrate-fed fish had higher survival rate when exposed to A. hydrophila. Moreover, the fenofibrate-fed fish also had higher activities of immune and antioxidative enzymes, and gene expressions of anti-inflammatory cytokines, while had lower expressions of pro-inflammatory cytokine genes. Taken together, PPARα activation improved the ability of Nile tilapia to resist A. hydrophila, mainly through enhancing mitochondrial fatty acids β-oxidation, immune and antioxidant capacities, as well as inhibiting inflammation. This is the first study showing the regulatory effects of PPARα activation on immune functions through increasing mitochondria-mediated energy supply in fish.

The effect of tertiary treated wastewater on fish growth and health: Laboratory-scale experiment with Poecilia reticulata (guppy)

Treated wastewater (TWW) constitutes a sustainable water resource and has been used for fish culture in some countries around the world, although there are no comprehensive data on the effect of TWW on fish growth and health in the context of aquaculture production. Our objectives were to examine how fish culture in TWW affected fish growth and fitness, as well as compliance with the international standards for safe consumption. Guppy (Poecilia reticulata) fingerlings were reared in 0%, 50% and 100% tertiary TWW (TTWW), from the age of five days, for a period of four months. In water analyses, 33 out of 67 tested organic micropollutants (OMPs) were detected in the TTWW samples at least once, at concentrations that are typically reported in domestic TTWW. Fish survival ranged between 77-80% and did not differ between treatment groups. Fish growth and mortality following challenge infection with Tetrahymena sp. (which ranged between 64-68%), were similar among treatment groups. Of tested immunological parameters, lysozyme and anti-protease was similar among treatments while complement activity was highest in the 50% TTWW-reared fish. No abnormalities were observed in the histopathological analysis. Levels of heavy metals, polychlorinated-biphenyls (PCBs) and organochlorines (OCs) in fish were below the detection limit and below the Food and Agriculture Organization of the United Nations (FAO) and the European Union EU maximal permitted levels in food fish. Results suggest that the yield of fish grown in TTWW is potentially similar to that in freshwater, and the produced fish comply with the standards of consumer safety. The results are in line with previous studies that examined the feasibility of TWW-fed aquaculture.

Molecular cloning and 3D model of a fatty-acid elongase in a carnivorous freshwater teleost, the European perch (Perca fluviatilis)

The European perch (Perca fluviatilis) is a carnivorous freshwater fish able to metabolise polyunsaturated fatty acids (PUFA) into highly unsaturated fatty acids (HUFA). This makes it a potential candidate for sustainable aquaculture development. In this study, special attention is given to the fatty-acid elongase (ELOVL) family, one of the two enzymatic systems implied in the HUFA biosynthesis. Structural information on European perch enzyme converting PUFA into HUFA is obtained by both molecular cloning and in silico characterization of an ELOVL5-like elongase from P. fluviatilis (pfELOVL). The full-length cDNA sequence consists of a 885-base pair Open Reading Frame coding for a 294-amino acid protein. Phylogenetic analysis and sequence alignment with fish elongases predict the pfELOVL clusters within the ELOVL5 sub-group. The amino-acid sequence displays the typical ELOVL features: several transmembrane α helices (TMH), an endoplasmic reticulum (ER) retention signal, and four "conserved boxes" involved in the catalytic site. In addition, the topology analysis predicts a 7-TMH structure addressed in the ER membrane. A 3D model of the protein embedded in an ER-like membrane environment is also provided using de novo modelling and molecular dynamics. From docking studies, two putative enzyme-substrate-binding modes, including H bonds and CH-π interactions, emphasize the role of specific residues in the "conserved boxes".

Lipid droplets participate in modulating innate immune genes in Ctenopharyngodon idella kidney cells

Lipid droplets (LDs) are increasingly being recognized as important immune modulators in mammals, in additional to their function of lipid ester deposition. However, the role of LDs in fish immunity remains poorly understood. In this study, the function of LDs in the innate immune response of Ctenopharyngodon idella kidney (CIK) cells, which are the equivalent of myeloid cells in vertebrates, was investigated. LD number and TG content significantly increased in the CIK cells following exposure to lipopolysaccharide (LPS), peptidoglycan (PGN), and polyriboinosinic-polyribocytidylic acid (Poly [I: C]) for 24 h, accompanied by increases in the relative expression of several innate immune genes. However, fatty acid compositions of the triglycerides were not changed after treatment with these three pathogenic mimics. LPS, PGN, and Poly (I: C) did not alter the relative expressions of lipogenic (FAS, SCD, and DGAT) and lipid catabolic (PPARα, ATGL, and CPT-1) genes. However, these treatments did increase the mRNA levels of lipid transportation genes (FATP/CD36, ACSL1, and ACSL4), and also decreased the non-esterified fatty acid level in the medium. To further explore the role of LDs in the immune response, CIK cells were incubated with different concentrations (0, 100, 200, 300, 400, 500 μM) of exogenous lipid mix (LM; oleic acid [OA]:linoleic acid [LA]:linolenic acid [LNA] = 2:1:1), and were then transferred to a lipid-free medium and incubated for 24 h. LD size and number increased with the increase in lipid levels, and this was accompanied by increased expression of innate immune genes, including MyD88, IRF3, and IL-1β, which were expressed at their highest levels in 300 μM exogenous lipid mix. Interestingly, after incubating with different fatty acids (LM, OA, LA, LNA, arachidonic acid [ARA], and docosahexaenoic acid [DHA]; 300 μM), ARA and DHA were more potent in inducing LD formation and innate immune gene expression in the CIK cells. Finally, atglistatin, an ATGL inhibitor, effectively attenuated the expression of most genes upregulated by ARA or DHA, suggesting that lipolysis may be involved in the regulation of immune genes at the transcriptional level. Overall, the findings of this study demonstrate that LDs are functional organelles that could act as modulators in the innate immune response of CIK cells. Additionally, long-chain polyunsaturated fatty acid enriched LDs play a unique role in regulating this process.

Innate immune responses and metabolic alterations of mud crab (Scylla paramamosain) in response to Vibrio parahaemolyticus infection

Vibrio parahaemolyticus is one of the major pathogens caused diseases in cultured mud crab (Scylla paramamosain). Mud crabs lack an adaptive immune system, their defenses depend almost on innate immunity. Evaluation of the molecular responses of mud crabs to pathogens is essential for control of disease occurrence in farmed animals. In this study, the impacts of V. parahaemolyticus on immunity-related genes and metabolites in mud crabs of different groups (PG, SG and MG refer to controlled, survival and moribund groups, respectively) were investigated. Our results revealed that V. parahaemolyticus infection stimulated significant expressions of immune-related genes (prophenoloxidase, alpha 2-macroglobulin, lysosomal-associated membrane protein, Rab5, C-type lectin B and anti-lipopolysaccharide factor 5) in the MG within 72 h post-infection. The ATP content was significantly reduced in all tissues except muscle of moribund mud crabs. A total of 668 metabolites (including 190 down-regulated and 145 up-regulated) were identified and assigned to 77 pathways in both SG and MG. Metabolites involved in the saturated fatty acid are up-regulated, whereas unsaturated fatty acid and amino acid metabolisms are down-regulated in the immune system of mud crabs during the bacterial infection in MG. Furthermore, a reduction of hemocyte number and an increase of microbial abundance was found in MG. Our results demonstrated that V. parahaemolyticus induced death of mud crabs through reducing the metabolites associate with energy biosynthesis and innate immune system (i.e. proliferation of hemocyte and melanization), resulting in decrease of ATP in different tissues and failed to clearance of pathogens, respectively. The findings of this study provide a basic information of the responses of mud crab on bacterial infection, which is essential for prevention and control of diseases in mud crab aquaculture.

Dietary Supplementation With ω6 LC-PUFA-Rich Algae Modulates Zebrafish Immune Function and Improves Resistance to Streptococcal Infection

Arachidonic acid (ARA, 20:4n-6) and dihomo-γ-linolenic acid (DGLA, 20:3n-6) are omega-6 long-chain polyunsaturated fatty acids (LC-PUFA), which are key precursors for lipid mediators of the immune system and inflammatory response. The microalga Lobosphaera incisa (WT) and its Δ5-desaturase mutant P127 (MUT) are unique photosynthetic sources for ARA and DGLA, respectively. This study explores the effect of dietary supplementation with L. incisa and P127 biomass on tissue fatty acid composition, immune function, and disease resistance in zebrafish (Danio rerio). The broken microalgal biomass was added to commercial fish feed at 7.5 and 15% (w/w), providing 21.8 mg/g feed ARA for the WT-supplemented group and 13.6 mg/g feed DGLA for the MUT-supplemented group at the 15% inclusion levels. An unsupplemented group was used as the control. After 1 month of feeding, fish were challenged with Streptococcus iniae. Fish were sampled before the challenge and 1 week after the challenge for various analyses. Tissue ARA and DGLA levels significantly increased in the liver, corresponding to microalgal supplementation levels. The elevated expression of specific immune-related genes was evident in the kidneys in all treatment groups after 1 month of feeding, including genes related to eicosanoid synthesis, lysozyme, and NF-κB. In the liver, microalgal supplementation led to the upregulation of genes related to immune function and antioxidant defense while the expression of examined genes involved in ARA metabolism was downregulated. Importantly, fish fed with 15% of both WT- and MUT-supplemented feed showed significantly (p < 0.05) higher survival percentages (78 and 68%, respectively, as compared to only 46% in the control group). The elevated expression of genes related to inflammatory and immune responses was evident post-challenge. Collectively, the results of the current study demonstrate the potential of microalgae-derived dietary ARA and DGLA in improving immune competence and resistance to bacterial infection in zebrafish as a model organism.