Arachidonic acid reduces the stress response of gilthead seabream Sparus aurata L

Spatial and ontogenetic modulation of fatty acid composition in juvenile European sea bass (Dicentrarchus labrax) from two French estuaries

This study evaluated how estuary of origin and ontogenetic stage influence the fatty acid (FA) composition in the tissues of wild European sea bass juvenile. We evidenced tissue-specific patterns, with the brain exhibiting a distinct FA composition from the liver and muscle. Ontogenetic stage and estuary influenced the general FA profile, and particularly the essential FA (EFA) like docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA) in all tissues. The data also revealed the ability of wild sea bass to modulate, at the molecular level, FA biosynthesis pathways and suggest a potential dietary DHA limitation in the natural environment. The distribution of FA within tissues might reflect shifts in diet, metabolic demands, or adaptations to environmental conditions. This study provides insights about FA dynamics in euryhaline fish during juvenile life stage, improving our understanding of the metabolism need and EFA trophic availability in a changing environment.

An integrative perspective on fish health: Environmental and anthropogenic pathways affecting fish stress

Multifactorial studies assessing the cumulative effects of natural and anthropogenic stressors on individual stress response are crucial to understand how organisms and populations cope with environmental change. We tested direct and indirect causal pathways through which environmental stressors affect the stress response of wild gilthead seabream in Mediterranean costal lagoons using an integrative PLS-PM approach. We integrated information on 10 environmental variables and 36 physiological variables into seven latent variables reflecting lagoons features and fish health. These variables concerned fish lipid reserves, somatic structure, inorganic contaminant loads, and individual trophic and stress response levels. This modelling approach allowed explaining 30 % of the variance within these 46 variables considered. More importantly, 54 % of fish stress response was explained by the dependent lagoon features, fish age, fish diet, fish reserve, fish structure and fish contaminant load latent variables included in our model. This integrative study sheds light on how individuals deal with contrasting environments and multiple ecological pressures.

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.

Effects of ocean acidification and warming on the development and biochemical responses of juvenile shrimp Palaemon elegans (Rathke, 1837)

Anthropogenic CO₂ emissions have led to the warming and acidification of the oceans. Although, there is a growing of evidence showing that simultaneous occurrence of ocean acidification and ocean warming are threats to marine organisms, information on their combined effect on coastal shrimp species remains scarce. The purpose of this study was to estimate the combined effects of seawater acidification and warming on growth-related traits and biochemical responses of P. elegans juveniles. In this work, shrimp were exposed for 65 days at 4 experimental conditions: pH 8.10 * 18 °C, pH 7.80 * 18 °C, pH 8.10 * 22 °C, pH 7.80 * 22 °C. The results showed that low pH decreases the lipid content by ∼13% (p < 0.05). Higher temperature reduced the condition factor by ∼11%, the protein content by ∼20%, the PUFA by ∼8,6% and shortened moulting events by 5 days (p > 0.05) while the SFA increased ∼9.4%. The decrease in condition factor and protein was however more prominent in organisms exposed to the combination of pH and temperature with a decrease of ∼13% and ∼21%, respectively. Furthermore, essential fatty acids as EPA and DHA also decreased by ∼20% and ∼6.6% in low pH and higher temperature condition. Despite this study suggest that warming may have a greater impact than acidification, it has been shown that their combined effect can exacerbate these impacts with consequences for the shrimp's body size and biochemical profile.

The dietary arachidonic acid improved growth and immunity of honey bee (Apis mellifera ligustica)

Honeybees cannot synthesize arachidonic acid (ARA) themselves, only obtain it from food. Most pollen is deficient or contains a small amount of ARA. The necessity of supplementary ARA in bees' diet has not been studied. The objective of this study was to investigate the effects of dietary ARA levels on the growth and immunity of Apis mellifera ligustica. A total of 25 honeybee colonies were randomly assigned to five dietary groups which were fed basic diets supplemented with 0, 2, 4, 6, and 8% of ARA. The diet with 4% ARA improved the body weight of newly emerged worker bees compared with the control group. Supplement of ARA in honeybee diets changed the fatty acid composition of honeybee body. SFA and MUFA contents of bees' body declined, and PUFA content rised in the ARA group. Compared with the control group, the supplement of ARA in honeybee diets increased the contents of ARA, C22:6n-3 (DHA) and C18:3n-6 in bees' body significantly, but decreased the contents of C16:1 and C18:3n-3. The diet supplied with 4% ARA reduced the mortality rate of honeybee infected with Escherichia coli. The activity of immune enzymes (phenoloxidase, antitrypsin, and lysozyme) and the mRNA expression levels of immune genes (defensin-2, toll, myd88, and dorsal) were improved by ARA diets to varying degrees depending on the ARA levels, especially 4% ARA. These results suggested that dietary ARA could improve the growth, survival, and immune functions of honeybees. Supplement of ARA in bees' diet would be valuable for the fitness of honeybees.

Low dietary inclusion of nutraceuticals from microalgae improves feed efficiency and modifies intermediary metabolisms in gilthead sea bream (Sparus aurata)

The aim of this work was to evaluate two functional feeds for the gilthead seabream, Sparus aurata, containing low inclusion of two microalgae-based products (LB-GREENboost, LB_Gb; and LB-GUThealth, LB_Gh). Fish (12–13 g) were fed for 13 weeks a control diet or one of the four diets supplemented with both products at 0.5% or 1%. LB_Gb and LB_Gh did not affect specific growth rate or survival, but increased feed efficiency by decreasing feed intake and enlarging the intestines. LB_Gb increased hepatosomatic index and reduced cortisol levels in plasma, while both products lowered plasma lactate. Extensive metabolite and metabolic enzyme profiling revealed that microalgae supplementations, especially 1% LB_Gh: (i) decrease plasma lactate and increase hepatic glycogen, (ii) reduce hepatic gluconeogenesis, (iii) enhance hepatic lipogenic activity and lipid secretion, (iv) led fish to double triglyceride content in muscle and to stimulate its lipid oxidative capacity, and (v) increase the content of monounsaturated fatty acids and the omega-3 alpha-linolenic acid in muscle. This study demonstrates that both microalgae-based products are suited to improve feed efficiency and orchestrate significant changes in the intermediary metabolism in gilthead seabream juveniles.

Prebiotics and phytogenics functional additives in low fish meal and fish oil based diets for European sea bass (Dicentrarchus labrax): Effects on stress and immune responses

The use of terrestrial raw materials to replace fish meal (FM) and fish oil (FO) in marine fish diets may affect fish growth performance and health. In the last years functional additives have been profiled as good candidates to reduce the effects on health and disease resistance derived from this replacement, via reinforcement of the fish immune system. In the present study, three isoenergetic and isonitrogenous diets with low FM and FO (10% and 6% respectively) were tested based on supplementation either with 0.5% galactomannanoligosaccharides (GMOS diet) or 0.02% of a mixture of essential oils (PHYTO diet), a non-supplemented diet was defined as a control diet. Fish were fed the experimental diets in triplicate for 9 weeks and then they were subjected to a stress by confinement as a single challenge (C treatment) or combined with an experimental intestinal infection with Vibrio anguillarum (CI treatment). Along the challenge test, selected stress and immunological parameters were evaluated at 2, 24 and 168h after C or CI challenges. As stress indicators, circulating plasma cortisol and glucose concentrations were analyzed as well as the relative gene expression of cyp11b hydroxylase, hypoxia inducible factor, steroidogenic acute regulatory protein, heat shock protein 70 and heat shock protein 90 (cyp11b, hif-1α, StAR, hsp70 and hsp90). As immune markers, serum and skin mucus lysozyme, bactericidal and peroxidase activities were measured, as well as gene expression of Caspase-3 (casp-3) and interleukin 1β (il-1ß). The use of functional additives induced a significant (p < 0.05) reduction of circulating plasma cortisol concentration when confinement was the unique challenge test applied. Supplementation of PHYTO induced a down-regulation of cyp11b, hif-1α, casp-3 and il-1β gene expression 2h after stress test, whereas StAR expression was significantly (p < 0.05) up-regulated. However, when combination of confinement stress and infection was applied (CI treatment), the use of PHYTO significantly (p < 0.05) down-regulated StAR and casp-3 gene expression 2h after challenge test, denoting that PHYTO diet reinforced fish capacity of stress response via protection of head kidney leucocytes from stress-related apoptotic processes, with lower caspase-3 gene expression and a higher il-1β gene expression when an infection occurs. Additionally, dietary supplementation with GMOS and PHYTO compounds increased fish serum lysozyme after infection. Both functional additives entailed a better capability of the animals to cope with infection in European sea bass when fed low FM and FO diets.

The Use of Dietary Additives in Fish Stress Mitigation: Comparative Endocrine and Physiological Responses

In the last years, studies on stress attenuation in fish have progressively grown. This is mainly due to the interest of institutions, producers, aquarists and consumers in improving the welfare of farmed fish. In addition to the development of new technologies to improve environmental conditions of cultured fish, the inclusion of beneficial additives in the daily meal in order to mitigate the stress response to typical stressors (netting, overcrowding, handling, etc.) has been an important research topic. Fish are a highly diverse paraphyletic group (over 27,000 species) though teleost infraclass include around 96% of fish species. Since those species are distributed world-wide, a high number of different habitats and vital requirements exist, including a wide range of environmental conditions determining specifically the stress response. Although the generalized endocrine response to stress (based on the release of catecholamines and corticosteroids) is detectable and therefore provides essential information, a high diversity of physiological effects have been described depending on species. Moreover, recent omics techniques have provided a powerful tool for detecting specific differences regarding the stress response. For instance, for transcriptomic approaches, the gene expression of neuropeptides and other proteins acting as hormonal precursors during stress has been assessed in some fish species. The use of different additives in fish diets to mitigate stress responses has been deeply studied. Besides the species factor, the additive type also plays a pivotal role in the differentiation of the stress response. In the literature, several types of feed supplements in different species have been assayed, deriving in a series of physiological responses which have not focused exclusively on the stress system. Immunological, nutritional and metabolic changes have been reported in these experiments, always associated to endocrine processes. The biochemical nature and physiological functionality of those feed additives strongly affect the stress response and, in fact, these can act as neurotransmitters or hormone precursors, energy substrates, cofactors and other essential elements, implying multi-systematic and multi-organic responses. In this review, the different physiological responses among fish species fed stress-attenuating diets based on biomolecules and minerals have been assessed, focusing on the endocrine regulation and its physiological effects.

Effects of dietary inclusions of red beet and betaine on the acute stress response and muscle lipid peroxidation in rainbow trout

This study evaluates the effects of red beet (RB) and betaine on rainbow trout submitted to an acute stress challenge. A control diet was compared with four experimental diets in which red beet (14 and 28%) and betaine (0.9 and 1.63%) were incorporated in different concentrations according to a factorial design. Cortisol in plasma and fin, glucose and lactate plasma levels, and malondialdehide (MDA) in muscle were all measured before the stress challenge and 30 min and 6 and 12 h after the stress challenge as parameters to determine the diet effects. RB and betaine had no effect on cortisol, glucose, and MDA basal levels. However, lactate basal levels were significantly lower on fish fed with RB and betaine. Thirty minutes after the stress challenge, there was a significant increase in plasma and fin cortisol, glucose and lactate concentrations, although fish fed with diets containing RB and betaine showed significantly higher plasma cortisol values. MDA values of fish fed with 14% RB and 0.9% betaine were significantly higher than MDA values from fish fed with 28% RB and 1.63% betaine. After 6 and 12 h, plasma and fin cortisol and lactate levels recovered in a similar trend. Glucose plasma levels recovered in almost all groups 12 h after the stress. Also, MDA values recovered basal levels after 6 and 12 h. RB and betaine did not enhance the tolerance to the stress challenge compared to the control group, although the presence of these ingredients had no negative effect on any of the stress indicators.

Influence of batch-specific biochemical egg characteristics on embryogenesis and hatching success in farmed pikeperch

Low and variable egg quality remains a major issue in aquaculture impeding a reliable and continuous supply of larvae, particularly in emerging species, such as pikeperch, Sander lucioperca. We assessed the influence of batch-specific egg parameters (fatty acid (FA) profiles, cortisol content) on embryo life-stages until hatching (survival at 2, 24, 48, 72 h post fertilization (hpf), hatching rate) in an integrated study under commercial hatchery conditions (44 egg batches). Embryo mortality was elevated until 48 hpf (average 9.8% mortality between 2 and 48 hpf). Embryos surviving until 48 hpf were very likely (98.5%) to hatch successfully. The inherent egg FA composition was variable in-between batches. Total FA content ranged form 66.1 to 171.7 µg/mg (dry matter) total FA. Whereas specific FA ,18 : 0 and 20 : 5(n-3) (eicosapentaenoic acid) of the polar fraction and the ratio of 22 : 6(n-3) (docosahexaenoic acid) to 20 : 5(n-3) within the neutral fraction, were significantly correlated with early embryo development, contents of the respective FA did not differ between high (>90% hatching rate), mid (70% to 90% hatching rate) and low (<70% hatching rate) quality egg batches. Late embryo development and hatching were relatively independent of the FA profiles highlighting stage-dependent influences especially during early embryogenesis. Cortisol levels ranged from 22.7 to 293.2 ng/ml and did not directly explain for mortalities. However, high cortisol was associated with a lower content of specific FA, in particular highly unsaturated FA. These results demonstrate the magnitude of inter-individual differences in the batch-specific biochemical egg composition under stable hatchery conditions and suggest a stress-mediated lack of essential FA, which in turn affects early embryo survival. Surprisingly, embryos are able to cope well with a broad range of inherent egg parameters, which limits their predictive potential for egg quality in general. Still, specific FA profiles of high quality egg batches have potential for formulating species-specific broodstock diets and improving reproductive management in pikeperch.

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.

Adaptive capacities from survival to stress responses of two isogenic lines of rainbow trout fed a plant-based diet

The composition of feed for farmed salmonids has strongly evolved during the last decades due to the substitution of fishery-derived fish oil and fishmeal by ingredients of plant origin. Little information is available regarding the effects of this transition on adaptive capacities in fish. Two rainbow trout isogenic lines, known for their divergent ability to grow on a plant-based diet (PBD), were fed for seven months from first feeding either a fully PBD or a control marine-resources diet and were compared for their growing and survival capacities over time and their behavioral and stress responses at similar sizes but different ages. Although fish displayed similar appetitive behaviour, the two lines were highly affected by the PBD translated in decreased growth and apathetic behaviour, but also stronger stress responses displayed by stronger cortisol increases and more stress-related behaviour when isolated. The two lines were found to be similarly sensitive to a PBD for the assessed stress-related parameters, but one line displayed a lower survival during the early rearing period. Overall, these results suggest that a PBD supplied to fish from the alevin stage has strong effects on physiological and behavioural parameters, with possible impairment of fish welfare, but also genome-dependent survival.

Replacement of Marine Fish Oil with de novo Omega-3 Oils from Transgenic Camelina sativa in Feeds for Gilthead Sea Bream (Sparus aurata L.)

Omega-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFA) are essential components of the diet of all vertebrates. The major dietary source of n-3 LC-PUFA for humans has been fish and seafood but, paradoxically, farmed fish are also reliant on marine fisheries for fish meal and fish oil (FO), traditionally major ingredients of aquafeeds. Currently, the only sustainable alternatives to FO are vegetable oils, which are rich in C18 PUFA, but devoid of the eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) abundant in FO. Two new n-3 LC-PUFA sources obtained from genetically modified (GM) Camelina sativa containing either EPA alone (ECO) or EPA and DHA (DCO) were compared to FO and wild-type camelina oil (WCO) in juvenile sea bream. Neither ECO nor DCO had any detrimental effects on fish performance, although final weight of ECO-fed fish (117 g) was slightly lower than that of FO- and DCO-fed fish (130 and 127 g, respectively). Inclusion of the GM-derived oils enhanced the n-3 LC-PUFA content in fish tissues compared to WCO, although limited biosynthesis was observed indicating accumulation of dietary fatty acids. The expression of genes involved in several lipid metabolic processes, as well as fish health and immune response, in both liver and anterior intestine were altered in fish fed the GM-derived oils. This showed a similar pattern to that observed in WCO-fed fish reflecting the hybrid fatty acid profile of the new oils. Overall the data indicated that the GM-derived oils could be suitable alternatives to dietary FO in sea bream.

Comparative Transcriptome Analysis in the Hepatopancreas Tissue of Pacific White Shrimp Litopenaeus vannamei Fed Different Lipid Sources at Low Salinity

RNA-seq was used to compare the transcriptomic response of hepatopancreas in juvenile Litopenaeus vannamei fed three diets with different lipid sources, including beef tallow (BT), fish oil (FO), and an equal combination of soybean oil + BT + linseed oil (SBL) for 8 weeks at 3 practical salinity unit (psu). A total of 9622 isogenes were annotated in 316 KEGG pathways and 39, 42 and 32 pathways significantly changed in the paired comparisons of FO vs SBL, BT vs SBL, or FO vs BT, respectively. The pathways of glycerolipid metabolism, linoleic acid metabolism, arachidonic acid metabolism, glycerophospholipid metabolism, fatty acid biosynthesis, fatty acid elongation, fatty acid degradation, and biosynthesis of unsaturated fatty acid were significantly changed in all paired comparisons between dietary lipid sources, and the pathways of glycerolipid metabolism, linoleic acid metabolism, arachidonic acid metabolism and glycerophospholipid metabolism significantly changed in the FO vs SBL and BT vs SBL comparisons. These pathways are associated with energy metabolism and cell membrane structure. The results indicate that lipids sources affect the adaptation of L. vannamei to low salinity by providing extra energy or specific fatty acids to change gill membrane structure and control iron balance. The results of this study lay a foundation for further understanding lipid or fatty acid metabolism in L. vannamei at low salinity.

Arachidonic Acid and Eicosapentaenoic Acid Metabolism in Juvenile Atlantic Salmon as Affected by Water Temperature

Salmons raised in aquaculture farms around the world are increasingly subjected to sub-optimal environmental conditions, such as high water temperatures during summer seasons. Aerobic scope increases and lipid metabolism changes are known plasticity responses of fish for a better acclimation to high water temperature. The present study aimed at investigating the effect of high water temperature on the regulation of fatty acid metabolism in juvenile Atlantic salmon fed different dietary ARA/EPA ratios (arachidonic acid, 20:4n-6/ eicosapentaenoic acid, 20:5n-3), with particular focus on apparent in vivo enzyme activities and gene expression of lipid metabolism pathways. Three experimental diets were formulated to be identical, except for the ratio EPA/ARA, and fed to triplicate groups of Atlantic salmon (Salmo salar) kept either at 10°C or 20°C. Results showed that fatty acid metabolic utilisation, and likely also their dietary requirements for optimal performance, can be affected by changes in their relative levels and by environmental temperature in Atlantic salmon. Thus, the increase in temperature, independently from dietary treatment, had a significant effect on the β-oxidation of a fatty acid including EPA, as observed by the apparent in vivo enzyme activity and mRNA expression of pparα -transcription factor in lipid metabolism, including β-oxidation genes- and cpt1 -key enzyme responsible for the movement of LC-PUFA from the cytosol into the mitochondria for β-oxidation-, were both increased at the higher water temperature. An interesting interaction was observed in the transcription and in vivo enzyme activity of Δ5fad-time-limiting enzyme in the biosynthesis pathway of EPA and ARA. Such, at lower temperature, the highest mRNA expression and enzyme activity was recorded in fish with limited supply of dietary EPA, whereas at higher temperature these were recorded in fish with limited ARA supply. In consideration that fish at higher water temperature recorded a significantly increased feed intake, these results clearly suggested that at high, sub-optimal water temperature, fish metabolism attempted to increment its overall ARA status -the most bioactive LC-PUFA participating in the inflammatory response- by modulating the metabolic fate of dietary ARA (expressed as % of net intake), reducing its β-oxidation and favouring synthesis and deposition. This correlates also with results from other recent studies showing that both immune- and stress- responses in fish are up regulated in fish held at high temperatures. This is a novel and fundamental information that warrants industry and scientific attention, in consideration of the imminent increase in water temperatures, continuous expansion of aquaculture operations, resources utilisation in aquafeed and much needed seasonal/adaptive nutritional strategies.

Transcriptome and Molecular Pathway Analysis of the Hepatopancreas in the Pacific White Shrimp Litopenaeus vannamei under Chronic Low-Salinity Stress

The Pacific white shrimp Litopenaeus vannamei is a euryhaline penaeid species that shows ontogenetic adaptations to salinity, with its larvae inhabiting oceanic environments and postlarvae and juveniles inhabiting estuaries and lagoons. Ontogenetic adaptations to salinity manifest in L. vannamei through strong hyper-osmoregulatory and hypo-osmoregulatory patterns and an ability to tolerate extremely low salinity levels. To understand this adaptive mechanism to salinity stress, RNA-seq was used to compare the transcriptomic response of L. vannamei to changes in salinity from 30 (control) to 3 practical salinity units (psu) for 8 weeks. In total, 26,034 genes were obtained from the hepatopancreas tissue of L. vannamei using the Illumina HiSeq 2000 system, and 855 genes showed significant changes in expression under salinity stress. Eighteen top Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were significantly involved in physiological responses, particularly in lipid metabolism, including fatty-acid biosynthesis, arachidonic acid metabolism and glycosphingolipid and glycosaminoglycan metabolism. Lipids or fatty acids can reduce osmotic stress in L. vannamei by providing additional energy or changing the membrane structure to allow osmoregulation in relevant organs, such as the gills. Steroid hormone biosynthesis and the phosphonate and phosphinate metabolism pathways were also involved in the adaptation of L. vannamei to low salinity, and the differential expression patterns of 20 randomly selected genes were validated by quantitative real-time PCR (qPCR). This study is the first report on the long-term adaptive transcriptomic response of L. vannamei to low salinity, and the results will further our understanding of the mechanisms underlying osmoregulation in euryhaline crustaceans.

The effects of arachidonic acid on the endocrine and osmoregulatory response of tilapia (Oreochromis mossambicus) acclimated to seawater and subjected to confinement stress

In previous studies in freshwater tilapia (Oreochromis mossambicus), dietary supplementation with arachidonic acid (ArA; 20:4n - 6) had considerable, opposing effects on the main ion-transporting enzyme Na(+)/K(+)-ATPase in gills and kidneys and changed the release of osmoregulatory hormones, such as cortisol. The present study was performed to assess the influence of dietary ArA on (1) the osmoregulatory capacity of tilapia acclimated to seawater (SW) (34‰) and (2) the osmoregulatory imbalance associated with acute stress. The increased ambient salinity was associated with significant alterations in the tissue fatty acid composition, particularly the n - 6 polyunsaturated fatty acids (PUFAs). Tissue levels of ArA were further increased as a result of dietary supplementation, whereas docosahexaenoic acid (DHA, 22:6n - 3) and eicosapentaenoic acid (EPA, 20:5n - 3) decreased in gills and kidneys. Basal plasma cortisol as well as lactate levels were elevated in the ArA-supplemented SW-acclimated tilapia compared with the control group. The 5 min of confinement (transient stress) increased plasma cortisol, glucose, and lactate levels with significantly higher levels in ArA-supplemented tilapia. Confinement was also associated with significantly elevated plasma osmolality, sodium, chloride, and potassium levels. ArA-supplemented tilapia showed markedly lower ionic disturbances after confinement, suggesting that dietary ArA can attenuate the hydromineral imbalance associated with acute stress. These results emphasize the involvement of ArA and/or its metabolites in the endocrine and osmoregulatory processes and the response to confinement stress.

Species specificity in the magnitude and duration of the acute stress response in Mediterranean marine fish in culture

The aim of the present study was to examine the species-specific stress response for seven Mediterranean fishes in culture. Also, to evaluate the method of measuring free cortisol concentration in the rearing water as a non-invasive and reliable indicator of stress in marine species, of aquaculture importance. Gilthead sea bream, Sparus aurata (Sparidae); common dentex, Dentex dentex (Sparidae); common Pandora, Pagellus erythrinus (Sparidae); sharpsnout sea bream, Diplodus puntazzo (Sparidae); dusky grouper, Epinephelus marginatus (Serranidae); meagre, Argyrosomus regius (Sciaenidae) and European sea bass, Dicentrarchus labrax (Moronidae) were subjected to identical acute stress (5-6 min chasing and 1-1.5 min air exposure) under the same environmental conditions and samples were analyzed by the same procedures. Results indicated that there was a clear species-specificity in the magnitude, timing and duration of the stress response in terms of cortisol, glucose and lactate. European sea bass showed a very high response and dusky grouper and meagre a very low response, except plasma glucose concentrations of dusky grouper which was constantly high, while sharpsnout sea bream presented a protracted stress response, up to 8h. The present study confirmed that free cortisol release rate into the water can be used as a reliable stress indicator.

The influence of dietary supplementation of arachidonic acid on prostaglandin production and oxidative stress in the Pacific oyster Crassostrea gigas

In a previous study, dietary supplementation with arachidonic acid (ARA) to oysters Crassostrea gigas increased haemocyte numbers, phagocytosis, and production of reactive oxygen species level (ROS) by haemocytes (Delaporte et al., 2006). To assess if the observed stimulation of these cellular responses resulted from changes of ARA-related prostaglandin (PG) production, we analysed prostaglandin E2 metabolite (PGEM) content on the same oysters fed three levels of ARA. Dietary supply of polyunsaturated fatty acids (PUFA) could also induce an oxidative stress that could similarly increase cellular responses; therefore, two indicators of oxidative stress were analysed: peroxidation level and antioxidant defence status. Together the observed positive correlation between ARA and PGEM levels and the absence of lipid peroxidation and antioxidant activity changes supports the hypothesis of an immune stimulation via PG synthesis. Although ARA proportion in oyster tissues increased by up to 7-fold in response to ARA dietary supplementation, peroxidation index did not change because of a compensatory decrease in n-3 fatty acid proportion, mainly 22:6n-3. To further confirm the involvement of PG in the changes of haemocyte count, phagocytosis and ROS production upon ARA supplementation, it would be interesting to test cyclooxygenase and lipooxygenase inhibitors in similar experiments.

The combined impact of plant-derived dietary ingredients and acute stress on the intestinal arachidonic acid cascade in Atlantic salmon (Salmo salar)

A study was conducted to assess the effect of substituting high levels of dietary fish oil (FO) and fishmeal (FM) for vegetable oil (VO) and plant protein (PP) on the intestinal arachidonic acid (AA) cascade in the carnivorous fish species Atlantic salmon. Four diets were fed to salmon over a period of 12 months, including a control FMFO diet, with varying replacements of plant-derived ingredients: 80 % PP and 35 % VO; 40 % PP and 70 % VO; 80 % PP and 70 %VO. Subsequently, fish were examined pre- (0 h) and post- (1 h) acute stress for blood parameters and intestinal bioactive lipidic mediators of inflammation (prostaglandins). Plasma cortisol responses were greatest in the FMFO group, while 80 % PP and 70 % VO fish exhibited increased plasma chloride concentrations. The n-3:n-6 PUFA ratio in intestinal glycerophospholipids from 70 % VO groups significantly decreased in both proximal and distal regions due to elevated levels of 18 : 2n-6 and the elongation/desaturation products 20 : 2n-6 and 20 : 3n-6. Increases in n-6 PUFA were not concomitant with increased AA, although the AA:EPA ratio did vary significantly. The 40 % PP and 70 % VO diet produced the highest intestinal AA:EPA ratio proximally, which coincided with a trend in elevated levels of PGF2alpha, PGE2 and 6-keto-PGF1alpha in response to stress. PGE2 predominated over PGF2alpha and 6-keto-PGF1alpha (stable metabolite of PGI2) with comparable concentrations in both intestinal regions. Cyclo-oxygenase-2 (COX-2) mRNA expression was an order of magnitude higher in distal intestine, compared with proximal, and was significantly up-regulated following stress. Furthermore, the 80 % PP and 70 % VO diet significantly amplified proximal COX-2 induction post-stress. Results demonstrate that high replacements with plant-derived dietary ingredients can enhance COX-2 induction and synthesis of pro-inflammatory eicosanoids in the intestine of salmon in response to acute physiological stress.

Variation in fatty acid composition of Artemia salina nauplii enriched with microalgae and baker's yeast for use in larviculture

The high content of the essential fatty acids in some microalgae and baker's yeast has made them excellent diets for boosting the fatty acid content of livefood Artemia. The influences of baker's yeast (Saccharomyces cerevisiae) and three microalgae, viz., Chlorella salina, Chaetoceros calcitrans, and Nannochloropsis salina, were tested as diet components in marine livefeed brine shrimp Artemia salina nauplii to improve the polyunsaturated fatty acid (PUFA) composition. Artemia nauplii submerged in these diets for four different enrichment intervals (3, 6, 8, and 24 h) were found to incorporate essential fatty acids, and the percentage composition of different fatty acids was measured in the enriched Artemia nauplii and enrichment diets. N. salina produced higher levels of arachidonic acid (AA, 20:4n6, 9.50%), eicosapentaenoic acid (EPA, 20:5n3, 25.80%), and docosahexaenoic acid (DHA, 22:6n3, 4.18%) as compared to other diets. The total PUFA content of the enriched Artemia by N. salina increased by 56.50% with enrichment periods up to 8 h, followed by a significant reduction in the final 24 h. N. salina yielded Artemia nauplii with considerable EPA (8.05%), AA (14.15%), and DHA (1.85%) after 8 h of enrichment, which are significantly higher levels than in nauplii fed with the other three diets (p = 0.05). The DHA/EPA values in Artemia enriched for 6 h by N. salina and C. calcitrans were found to be, respectively, 88.46 and 25% higher than freshly hatched Artemia. Artemia enriched by C. salina and baker's yeast exhibited a reduction in PUFA content even at 6 h of enrichment. Significant relative decreases in DHA, EPA, and total PUFA in Artemia enriched with all of the diets were apparent, with a corresponding increase in the total saturated fatty acid content (26.95 +/- 9.75%) in the final stages (24 h) of enrichment (p = 0.05).

Salicylate disrupts interrenal steroidogenesis and brain glucocorticoid receptor expression in rainbow trout

Varying levels of pharmaceuticals, including salicylate, ibuprofen, and acetaminophen, have been reported in the aquatic environment, but few studies have actually addressed the impact of these drugs on aquatic organisms. We tested the hypothesis that these pharmaceuticals are endocrine disruptors in fish by examining their impact on interrenal corticosteroidogenesis in rainbow trout. Indeed, acute adrenocorticotrophic hormone (ACTH)-mediated cortisol production in trout interrenal cells in vitro was significantly depressed (20-40%) by these pharmaceutical drugs. Furthermore, we investigated whether this interrenal dysfunction involved inhibition of the steroidogenic capacity in rainbow trout. To this end, we fed trout salicylate-laced feed (100 mg/kg body weight) for 3 days and assessed the transcript levels of key proteins involved in corticosteroidogenesis, including steroidogenic acute regulatory protein (StAR), peripheral-type benzodiazepine receptor (PBR), cytochrome P450 cholesterol side chain cleavage (P450scc), and 11beta-hydroxylase. Salicylate treatment did not affect the resting plasma cortisol or glucose levels, whereas the acute ACTH-stimulated cortisol production was significantly depressed in the interrenal tissue. This disruption of steroidogenesis by salicylate corresponded to a significant drop in the gene expression of StAR and PBR, but not P450scc or 11beta-hydroxylase, compared to the sham-treated fish. Also, brain glucocorticoid receptor (GR) protein content and not GR mRNA level was significantly reduced by salicylate. Taken together, salicylate is a corticosteroid disruptor in trout and the targets include the key rate-limiting step in interrenal steroidogenesis and brain glucocorticoid signaling.

Incorporation and modification of dietary fatty acids in gill polar lipids by two bivalve species Crassostrea gigas and Ruditapes philippinarum

Two bivalve species Crassostrea gigas and Ruditapes philippinarum were fed eight weeks with three mono-specific algae diets: T-Isochrysis galbana, Tetraselmis suecica, Chaetoceros calcitrans, selected on the basis of their polyunsaturated fatty acid (PUFA) composition. The incorporation and the modification of dietary fatty acids in C. gigas and R. philippinarum gill lipids were analysed and compared. Essential PUFA (20:4n-6, 20:5n-3 and 22:6n-3) and non-methylene interrupted PUFAs (known to be synthesised from monounsaturated precursors) contents of gill polar lipid of both species were greatly influenced by the dietary conditioning. Interestingly, oysters and clams responded differentially to the mono-specific diets. Oysters maintained higher 20:5n-3 level and higher 22:2j/22:i and n-7/n-9 ratio in gill polar lipids than clams. To better discriminate dietary and species influences on the fatty acid composition, a Principal Component Analysis followed by a MANOVA on the two most explicative components was performed. These statistical analyses showed that difference in fatty acid compositions attributable to species were just as significant as the diet inputs. The differences of gill fatty acid compositions between oysters and clams are speculated to result of an intrinsic species characteristic and perhaps of a group characteristic: Fillibranch vs. Eulamellibranch.