Dietary docosahexaenoic acid is more optimal than eicosapentaenoic acid affecting the level of cellular defence responses of the juvenile grouper Epinephelus malabaricus

Thraustochytrids as a promising source of fatty acids, carotenoids, and sterols: bioactive compound biosynthesis, and modern biotechnology

Thraustochytrids are eukaryotes and obligate marine protists. They are increasingly considered to be a promising feed additive because of their superior and sustainable application in the production of health-benefiting bioactive compounds, such as fatty acids, carotenoids, and sterols. Moreover, the increasing demand makes it critical to rationally design the targeted products by engineering industrial strains. In this review, bioactive compounds accumulated in thraustochytrids were comprehensively evaluated according to their chemical structure, properties, and physiological function. Metabolic networks and biosynthetic pathways of fatty acids, carotenoids, and sterols were methodically summarized. Further, stress-based strategies used in thraustochytrids were reviewed to explore the potential methodologies for enhancing specific product yields. There are internal relationships between the biosynthesis of fatty acids, carotenoids, and sterols in thraustochytrids since they share some branches of the synthetic routes with some intermediate substrates in common. Although there are classic synthesis pathways presented in the previous research, the metabolic flow of how these compounds are being synthesized in thraustochytrids still remains uncovered. Further, combined with omics technologies to deeply understand the mechanism and effects of different stresses is necessary, which could provide guidance for genetic engineering. While gene-editing technology has allowed targeted gene knock-in and knock-outs in thraustochytrids, efficient gene editing is still required. This critical review will provide comprehensive information to benefit boosting the commercial productivity of specific bioactive substances by thraustochytrids.

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.

Long-Chain Polyunsaturated Fatty Acids n−3 (n−3 LC-PUFA) as Phospholipids or Triglycerides Influence on Epinephelus marginatus Juvenile Fatty Acid Profile and Liver Morphophysiology

Simple Summary

Fish feeding is responsible for almost 60% of the total cost of marine fish production, so nutritional studies are always in demand. Dusky grouper is a promising species for aquaculture, but studies of the species’ nutrition are still lacking. The present study investigated the effects of fatty acids, provided as different lipid classes in four different diets, for Epinephelus marginatus fingerlings and evaluated their physiological and morphological responses in order to provide new insights about grouper nutrition. The fatty acids, provided as different lipid classes, modified the physiological and morphological responses of E. marginatus, showing that the inclusion of these lipids as different classes should be considered in order to obtain better results in terms of fish fillet quality. These results provided valuable insights into the nutrition and physiology of dusky groupers, helping to pave the way for the establishment of this fish species as a produced species worldwide.

Abstract

Phospholipids (PL) are membrane components composed of fatty acids (FA), while triglycerides (TG) are a main source of energy and essential FA. Polyunsaturated FA (PUFA), such as docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), are essential for marine carnivorous fish; thus, an 8-week experiment was performed to evaluate the influence of DHA and EPA, provided as PL and TG, on the morphophysiology of Epinephelus marginatus juveniles. A basal diet was manufactured, and DHA and EPA in PL form (PL1—low amount PL2—high amount) and TG form (TG1—low amount; TG2—high amount) were added. Dusky grouper juveniles were equally distributed in 12 tanks of 20 animals each, and liver and muscle were sampled for metabolic analysis. The total hepatic lipids in PL1 and PL2 were higher when compared to the initial, TG1 and TG2 groups. Total lipids in muscle were higher in PL2 and TG1 than PL1 and TG2, respectively. Diets rich in DHA and EPA in PL and TG resulted in higher deposition of these FA in the muscle polar fraction. However, fish fed diets containing lower amounts of DHA and EPA in PL and TG stored those in the muscle neutral fraction and liver, centralizing the storage of DHA and EPA.

Mitigating multiple stresses in Pangasianodon hypophthalmus with a novel dietary mixture of selenium nanoparticles and Omega-3-fatty acid

Effects of a novel dietary mixture of selenium nanoparticles (Se-NPs) and omega-3-fatty acids i.e., Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on mitigating arsenic pollution, high-temperature stress and bacterial infection were investigated in Pangasianodon hypophthalmus. To aim this, four isocaloric and iso-nitrogenous diets were prepared: control feed (no supplementation), Se-NPs at 0.2 mg kg^-1 diet with EPA + DHA at 0.2, 0.4 and 0.6% as supplemented diets. Fish were reared under normal condition or concurrent exposure to arsenic (2.65 mg L^-1), and temperature (34 °C) (As + T) stress for 105 days. The experiment was conducted with eight treatments in triplicates. Response to various stresses i.e., primary (cortisol), secondary (oxidative stress, immunity, and stress biomarkers) and tertiary stress response (growth performance, bioaccumulation and mortality due to bacterial infection) were determined. Supplementation of dietary Se-NPs at 0.2 mg kg^-1 diet and EPA + DHA at 0.2 and 0.4% reduced the primary stress level. Exposure to arsenic and temperature (As + T) and fed with control diet and EPA + DHA at 0.6% aggravated the cortisol level. Anti-oxidative enzymes (Catalase, superoxide dismutase, glutathione peroxidase and glutathione-s-transferase) and immunity (Nitroblue tetrazolium, total protein, albumin, globulin, A:G ratio, total immunoglobulin and myeloperoxidase) of the fish were augmented by supplementation of Se-NPs and EPA + DHA at 0.2 and 0.4%. Neurotransmitter enzyme, HSP 70, Vitamin C were significantly enhanced (p < 0.01) with supplementation of Se-NPs at 0.2 mg kg^-1 and EPA + DHA at 0.2 and 0.4%. Whereas total lipid, cholesterol, phospholipid, triglyceride and very low-density lipoprotein (VLDL) were reduced (p < 0.01) with the supplementation of Se-NPs at 0.2 mg kg^-1 diet and EPA + DHA at 0.2 and 0.4%. Tertiary stress response viz. growth performance was also significantly enhanced with supplementation of Se-NPs at 0.2 mg kg^-1 and EPA + DHA at 0.2 and 0.4% reared under As + T. Whereas arsenic bioaccumulation in fish tissues was significantly reduced with dietary supplementation of Se-NPs and EPA + DHA. Cumulative mortality and relative percentage survival were reduced with Se-NPs at 0.2 mg kg^-1 and EPA + DHA at 0.2 and 0.4%. The investigation revealed that a novel combination of Se-NPs at 0.2 mg kg^-1 and EPA + DHA at 0.4% followed by 0.2% has the potential to alleviate temperature stress, bacterial infection and arsenic pollution. Whereas diet containing Se-NPs at 0.2 mg kg^-1 diet and EPA + DHA at 0.6% was noticeably enhanced the stress in P. hypophthalmus.

Ameliorative effect of docosahexaenoic acid on hepatocyte apoptosis and inflammation induced by oleic acid in grass carp, Ctenopharyngodon idella

Our previous study has shown that overload of lipid accumulation results in cell apoptosis and inflammation in grass carp (Ctenopharyngodon idella). In this study, we investigated the potential protective effects of docosahexaenoic acid (DHA) on inhibiting oleic acid (OA)-induced apoptosis and inflammation in grass carp hepatocytes. Firstly, the hepatocyte of grass carp were treated with OA (800 μM) and different concentration (0, 50, 100 and 200 μM) of DHA for 24 h, the apoptotic ratio, gene expression levels of apoptosis such as caspase 3, caspase 8, and caspase 9, protein levels of Caspase3, and mRNA levels of inflammation genes such as nf-kb, tnf-α, and il-8 were detected. Furthermore, the mRNA levels of lipogenesis genes srebp1c, fas, acc, and scd and a key enzyme of lipolysis Atgl were also detected. These results showed that the cell apoptosis and the inflammation increased by OA were significantly attenuated by DHA (P < 0.05). Furthermore, DHA could significantly decrease fatty acid synthesis gene expression levels which were induced by OA (P < 0.05). However, the hepatocytes exposed with DHA had no significant influence on the expression of Atgl. Taken together, the study indicated that DHA protects the hepatocytes against apoptosis and inflammation induced by OA might via inhibiting fatty acid synthesis, instead of promoting lipolysis. These results call for further studies to assess the effectiveness of DHA.

Ocean warming combined with lower omega-3 nutritional availability impairs the cardio-respiratory function of a marine fish

Highly unsaturated fatty acids of the omega-3 series (HUFA) are major constituents of cell membranes, yet are poorly synthesised de novo by consumers. Their production, mainly supported by aquatic microalgae, has been decreasing with global change. The consequences of such reductions may be profound for ectotherm consumers, as temperature tightly regulates the HUFA content in cell membranes, maintaining their functionality. Integrating individual, tissue and molecular approaches, we examined the consequences of the combined effects of temperature and HUFA depletion on the key cardio-respiratory functions of the golden grey mullet, an ectotherm grazer of high ecological importance. For 4 months, fish were exposed to two contrasting HUFA diets [4.8% eicosapentaenoic acid (EPA)+docosahexaenoic acid (DHA) on dry matter (DM) versus 0.2% EPA+DHA on DM] at 12 and 20°C. Ventricular force development coupled with gene expression profiles measured on cardiac muscle suggest that combining HUFA depletion with warmer temperatures leads to: (1) a proliferation of sarcolemmal and sarcoplasmic reticulum Ca²⁺ channels and (2) a higher force-generating ability by increasing extracellular Ca²⁺ influx via sarcolemmal channels when the heart has to sustain excessive effort due to stress and/or exercise. At the individual scale, these responses were associated with a greater aerobic scope, maximum metabolic rate and net cost of locomotion, suggesting the higher energy cost of this strategy. This impaired cardiac performance could have wider consequences for other physiological performance such as growth, reproduction or migration, all of which greatly depend on heart function.

Transcriptomic Analysis of Potential "lncRNA-mRNA" Interactions in Liver of the Marine Teleost Cynoglossus semilaevis Fed Diets With Different DHA/EPA Ratios

Long non-coding RNAs (lncRNA) have emerged as important regulators of lipid metabolism and have been shown to play multifaceted roles in controlling transcriptional gene regulation, but very little relevant information has been available in fish, especially in non-model fish species. With a feeding trial on a typical marine teleost tongue sole C. semilaevis followed by transcriptomic analysis, the present study investigated the possible involvement of lncRNA in hepatic mRNA expression in response to different levels of dietary DHA and EPA, which are two most important fatty acids for marine fish. An 80-day feeding trial was conducted in a flow-through seawater system, and in this trial three experimental diets differing basically in DHA/EPA ratio, i.e., 0.61 (D/E-0.61), 1.46 (D/E-1.46), and 2.75 (D/E-2.75), were randomly assigned to 9 tanks of experimental fish. A total of 124.04 G high quality genome-wide clean data about coding and non-coding transcripts was obtained in the analysis of hepatic transcriptome. Compared to diet D/E-0.61, D/E-1.46 up-regulated expression of 178 lncRNAs and 2629 mRNAs, and down-regulated that of 47 lncRNAs and 3059 mRNAs, while D/E-2.75 resulted in much less change in gene expression. The co-expression and co-localization analysis of differentially expressed (DE) lncRNA and mRNA among dietary groups were then conducted. The co-expressed DE lncRNA and mRNA were primarily enriched in GO terms such as Metabolic process, Intracellular organelle, Catalytic activity, and Oxidoreductase activity, as well as in KEGG pathways such as Ribosome and Oxidative phosphorylation. Overlap of co-expression and co-localization analysis, i.e., lncRNA–mRNA matches “XR_523541.1–solute carrier family 16, member 5 (slc16a5)” and “LNC_000285–bromodomain adjacent to zinc finger domain 2A (baz2a),” were observed in all inter-group comparisons, indicating that they might crucially mediate the effects of dietary DHA and EPA on hepatic gene expression in tongue sole. In conclusion, this was the first time in marine teleost to investigate the possible lncRNA–mRNA interactions in response to dietary fatty acids. The results provided novel knowledge of lncRNAs in non-model marine teleost, and will serve as important resources for future studies that further investigate the roles of lncRNAs in lipid metabolism of marine teleost.

Effect of alkoxy glycerol on growth performance, immune response and disease resistance in Nile Tilapia (Oreochromis niloticus)

Fish oil and their compounds derived from the same have immense applications in the improvement of health, brain development, enhancing immunity etc. This study aimed at the supplementation of such a compound alkoxy glycerol derived from shark liver oil in fish diet and thereby analyzing growth as well as immune parameters of Oreochromis niloticus. 400 fishes were distributed into 11 glass tanks, and then fishes were weighed before starting the experiment. (Average weight was found to be 5.3 ± 0.10 g). Feed was prepared using alkoxy glycerol in the doses like 5, 10, 15 g kg^-1 Fishes were fed with the prepared diet for 30 days and growth parameters like specific growth rate (SGR), weight gain (WG), final weight (FW), and feed conversion ratio (FCR) were measured. On the 30th day, fishes were challenged with 0.1 ml of normal saline solution containing 10⁷ CFUml^-1 of Aeromonas hydrophila and disease resistance was monitored. After 30 days of post challenge observation, immunological and lipid peroxidation assays like alternative complement (ACH50), phagocytosis (PI), respiratory burst activities (RB), and serum lysozyme (SL) were performed.

Docosahexaenoic acid induces PPARγ-dependent preadipocytes apoptosis in grass carp Ctenopharyngodon idella

Our previous study showed that docosahexaenoic acid (DHA) plays an important role in decreasing lipid accumulation by inducing apoptosis of the adipocytes in grass carp. However, the mechanism involved remains unclear. DHA has been reported as the natural ligand of PPARγ. The present study aimed to assess whether PPARγ mediates the pro-apoptotic effects by DHA. Adipocytes of grass carp were cultured until 2 days post-confluence and were treated with DHA at various concentrations-0, 25, 50, 100, 200, and 400 μmol/L for 24 h and at 200 μmol/L for various time periods (0, 12, 24, and 48 h, respectively). Besides, the adipocytes were exposed to 200 μM DHA and PPARγ antagonist or inhibitor of certain key enzymes of apoptosis, following which the expression levels of key genes of the cell apoptotic and mitochondrial apoptotic pathways were detected. We found that DHA induced apoptosis of grass carp adipocytes in a time- and dose-dependent manner (P < 0.05). In addition, DHA treatment significantly increased the protein and gene expression levels of PPARγ (P < 0.05), but the PPARγ antagonist significantly abolished this effect and the DHA pro-apoptotic effect (P < 0.05). Moreover, treatment with caspase 9 inhibitor significantly attenuated the DHA-induced preadipocytes apoptosis effects, while treatment with caspase 8 inhibitor showed no influence. These observations suggest that the DHA-induced apoptosis in adipocytes might be mediated by PPARγ and via the intrinsic apoptotic pathway in grass carp.

The short-term effects of farmed fish food consumed by wild fish congregating outside the farms

We simulated in the laboratory the possible effects on fatty acids and immune status of wild fish arriving for the first time in the vicinity of a sea-cage fish farm, shifting their natural diet to commercial feed consumption, rich in fatty acids of vegetable origin. The flesh fatty acid profile of golden mullet specimens was altered after 2weeks of commercial feed consumption, showing an increase in fatty acids of vegetable origin. The serum peroxidase and bactericidal activities, and head-kidney leucocyte phagocytic capacity, increased after eight weeks of the new diet, while the respiratory burst activity decreased. The extent of these changes cannot be considered large enough to regard them as compromising the health status of fish. More research is needed in order to elucidate whether the rapid assimilation of the dietary fatty acids could harm the immune status of fish when feeding for longer periods than two months.

A comparative study: In vitro effects of EPA and DHA on immune functions of head-kidney macrophages isolated from large yellow croaker (Larmichthys crocea)

Comparative effects of different concentrations of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on immune responses of head-kidney macrophages isolated from large yellow croaker were studied in vitro. After exposing to serum-free medium for 1 day, cultured cells were incubated in medium supplemented with graded levels of EPA or DHA (0, 5, 25, 100, 200 and 1000 μM, respectively) in the form of fatty acid bovine serum albumin (FA-BSA) complex for 12 h, 24 h and 36 h, respectively. Control samples were incubated in the absence of EPA or DHA (2% bovine serum albumin, BSA). Following stimulation, cell viability, lipid peroxidation, secretary phopholipase A2 (sPLA2) and prostaglandin E2 (PGE2) production as well as some immune parameters including phagocytosis, respiratory burst activity and interleukin 1β (IL-1β) production were determined. Results showed that EPA and DHA affected cell viability in dose-dependent and time-dependent manners. In particular, cell viability was significantly decreased after 24 h and 36 h incubation with 1000 μM EPA or DHA (P < 0.05). Higher levels of EPA (200 and 1000 μM) caused a significant increase in the production of malondialdehyde (MDA) (P < 0.05), while DHA did not significantly affect the MDA production. EPA significantly increased the intracellular superoxide anion synthesis which, on the contrary, was significantly reduced by DHA. Phagocytosis percentage (PP) values were significantly higher in treatments with 5 μM DHA (P < 0.05), but significantly decreased by 200 and 1000 μM EPA and DHA compared to the control group (P < 0.05). Decreased PGE2 production was produced by cells treated with relatively low doses of EPA or DHA. When high levels of stimulants (1000 μM EPA or DHA) were used, PGE2 levels were elevated and reached a significant level (P < 0.05). Both EPA and DHA significantly inhibited the production of sPLA2, where DHA exerted the more potent inhibitory effects than EPA. No pronounced effect was observed on IL-1β production among all the treatments, and IL-1β level in cell culture supernatant was fairly low (only approximately 6 pg/ml). Those findings suggested that EPA and DHA could influence the immunity and physiological conditions of macrophages from head kidney of large yellow croaker in vitro.

Effects of dietary n-3 highly unsaturated fatty acids on growth, nonspecific immunity, expression of some immune related genes and disease resistance of large yellow croaker (Larmichthys crocea) following natural infestation of parasites (Cryptocaryon irritans)

The study was conducted to investigate the effects of dietary n-3 highly unsaturated fatty acid (n-3 HUFA) on growth, nonspecific immunity, expression of some immune related genes and disease resistance of juvenile large yellow croaker (Larmichthys crocea) following natural infestation of parasites (Cryptocaryon irritans). Six isoproteic and isolipidic diets were formulated with graded levels of n-3 HUFA ranging from 0.15% to 2.25% of the dry weight and the DHA/EPA was approximately fixed at 2.0. Each diet was randomly allocated to triplicate groups of fish in floating sea cages (1.0 × 1.0 × 1.5 m), and each cage was stocked with 60 fish (initial average weight 9.79 ± 0.6 g). Fish were fed twice daily (05:00 and 17:00) to apparent satiation for 58 days. Results showed that moderate n-3 HUFA level (0.98%) significantly enhanced growth compared with the control group (0.15% HUFA) (P < 0.05), while higher n-3 HUFA levels (1.37%, 1.79% and 2.25%) had detrimental effects on the growth though no significance was found (P > 0.05). Nitro blue tetrazolium (NBT) positive leucocytes percentage of head kidney and serum superoxide dismutase (SOD) activity increased with increasing n-3 HUFA from 0.15% to 0.60%, and decreased with further increase of n-3 HUFA from 0.60% to 2.25% (P < 0.05). Serum lysozyme activity increased significantly as n-3 HUFA increased from 0.15% to 1.37%, and then decreased with n-3 HUFA from 1.37% to 2.25% (P > 0.05). There were no significant differences in phagocytosis index (PI) of head kidney leucocytes among dietary treatments (P > 0.05). The hepatic mRNA expression of Toll-like receptor 22 (TLR22) and Myeloid differentiation factor 88 (MyD88) was significantly up-regulated in fish fed the diets with low or moderate levels, while in kidney this increment was only found at specific sampling time during the natural infestation of parasites. The 13 d cumulative mortality rate following natural infestation of parasites decreased with n-3 HUFA increased from 0.15% to 0.60% (P < 0.05), and significantly increased with n-3 HUFA from 0.60% to 2.25% (P < 0.05). Results of this study suggested that fish fed low or moderate dietary n-3 HUFA had higher growth, nonspecific immune responses, expression levels of some immune related genes and disease resistance of large yellow croaker following natural infestation of parasites and dietary n-3 HUFA may regulate fish immunity and disease resistance by altering the mRNA expression levels of TLR22 and MyD88.

Different ratios of docosahexaenoic and eicosapentaenoic acids do not alter growth, nucleic acid and fatty acids of juvenile cobia (Rachycentron canadum)

An experiment was performed to study the effect of different ratios of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) on the growth, nucleic acid and fatty acids of cobia (Rachycentron canadum) juveniles. The juveniles were fed for 8 weeks using seven treatment diets (D-1-D-7) with the same amount of DHA and EPA (1.50 +/- 0.1% of dried diet), but varying ratios of DHA to EPA (0.90, 1.10, 1.30, 1.50, 1.70, 1.90, 2.10, respectively) and a control diet (D-0, DHA + EPA = 0.8% of dried diet, DHA/EPA = 1.30). At the end of the experiment, the mean body weight (BW) of juveniles fed D-0-D-7 increased significantly (from 6.86 +/- 1.64 in the week 0 to 58.52 +/- 16.45 g at the end of week 8, P < 0.05). The mean RNA amount and RNA/DNA ratio in the muscle (from 39.62 +/- 1.30 microg mg(-1) and 2.29 +/- 0.11 in the week 0 to 272.55 +/- 10.70 microg mg(-1) and 14.54 +/- 1.75 at the end of week 8, respectively) and the mean weight in the liver (from 117.70 +/- 11.15 microg mg(-1) and 3.14 +/- 0.25 in the week 0 to 793.07 +/- 13.38 microg mg(-1) and 13.16 +/- 0.76 at the end of week 8, respectively) of cobia juveniles fed D-0-D-7 were significantly higher at the end of 8-week experiment than initially (P < 0.05). The RNA/DNA ratio in the muscle and liver of cobia juveniles increased with their growth and appeared an obvious positive relationship, especially in the muscle, based on regression analysis. The mean lipid content increased significantly in the liver (from 29.82 +/- 0.99 to 37.47 +/- 3.25% totally) and muscle (from 6.74 +/- 0.25 to 10.63 +/- 0.23% totally) of cobia juveniles (P < 0.05). However, no significant difference was found on the lipid contents of juveniles fed different diets for 8 weeks (P > 0.05). In the muscle and liver of juveniles, EPA decreased with its reduction in the diet; DHA, DHA/EPA ratio and poly unsaturated fatty acids (PUFAs) generally increased with their increment in the diet. The conclusion was drawn that the growth, nucleic acid and fatty acids of cobia juveniles were not significantly affected by different DHA/EPA ratios in our experiments.

Impact of 20∶4n−6 supplementation on the fatty acid composition and hemocyte parameters of the pacific oyster crassostrea gigas

Arachidonic acid (20:4n-6, ArA) and its eicosanoid metabolites have been demonstrated to be implicated in immune functions of vertebrates, fish, and insects. Thus, the aim of this study was to assess the impact of ArA supplementation on the FA composition and hemocyte parameters of oysters Crassostrea gigas. Oyster dietary conditioning consisted of direct addition of ArA solutions at a dose of 0, 0.25, or 0.41 microg ArA per mL of seawater into tanks in the presence or absence of T-Iso algae. Results showed significant incorporation of ArA into gill polar lipids when administered with algae (up to 19.7%) or without algae (up to 12.1%). ArA supplementation led to an increase in hemocyte numbers, phagocytosis, and production of reactive oxygen species by hemocytes from ArA-supplemented oysters. Moreover, the inhibitory effect of Vibrio aestuarianus extracellular products on the adhesive proprieties of hemocytes was lessened in oysters fed ArA-supplemented T-Iso. All changes in oyster hemocyte parameters reported in the present study suggest that ArA and/or eicosanoid metabolites affect oyster hemocyte functions.

Enhancement of EPA and DHA biosynthesis by over-expression of masu salmon Δ6-desaturase-like gene in zebrafish

The n - 3 polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have important nutritional benefits in humans. Farmed fish could serve as promising sources of EPA/DHA, but they need these fatty acids or their precursors in their diets. Here we transferred masu salmon delta6-desaturase-like gene in zebrafish to increase its ability for synthesizing EPA and DHA. Expression of this gene in transgenic fish elevated their EPA content by 1.4-fold and DHA by 2.1-fold. On the other hand, the alpha-linolenic acid (ALA) content decreased, it being a substrate of delta6-desaturase, while the total lipid remained constant. This achievement demonstrates that fatty acid metabolic pathway in fish can be modified by the transgenic technique, and perhaps this could be applied to tailor farmed fish as even better sources of valuable human food.