Changes in the fatty acid composition of phospholipids in tissues of farmed sea bass (Dicentrarchus labrax) during an annual cycle. Roles of environmental temperature and salinity

Dietary salt concentrations influence growth, nutrient utilization, and fatty acid profiles of turbot (Scophthalmus maximus) reared in brackish water

Expansion of economically viable turbot (Scophthalmus maximus) aquaculture depends on access to brackish-cold ground water sources in various parts of the world. Since brackish water sources can adversely affect the physiology and zoo technical performance of fish due to the burden of osmoregulation, dietary salt inclusion can alleviate the negative impacts of low-saline waters in several aquaculture species. This study investigated the effects of increasing dietary salt levels on the growth, feed utilization, body composition, and tissue fatty acid composition of juvenile turbot (initial live weight 120.3 ± 0.03 g/fish). Fish were fed five experimental diets supplemented with varying levels of sodium chloride (1.8-6.4%) or a control diet without salt. Each diet was tested in triplicate tanks for 9 weeks. Results showed that increasing dietary salt intake negatively impacted turbot performance, with significant reductions in weight gain, specific growth rate, and feed conversion ratio. Dry matter and ash content in the whole body and filet increased quadratically with increasing salt levels, whereas gill moisture and protein content decreased linearly. Furthermore, the nitrogen, lipid, and energy utilization efficiencies decreased with their respective intake and gain levels. Dietary salt significantly influenced the fatty acid profiles of gill, liver, and filet tissues. In the gill, monounsaturated fatty acids (16:1n-7, ΣMUFA) and n-6 PUFA (20:2n-6) increased, whereas EPA and DHA decreased. Liver ΣSFA (16:0, 18:0) increased, and n-3 PUFA (18:3n-3, 20:5n-3) decreased with increasing dietary salt. Filet saturated fatty acids (14:0, 15:0, 17:0) and n-6 PUFA (20:2n-6, 20:4n-6) increased, while n-3 PUFA (18:3n-3, EPA) decreased with dietary salt. DHA levels in filets showed a quadratic increase. Overall, this study shows that increasing dietary salt negatively impacts turbot growth, feed utilization, and tissue fatty acid composition in brackish water, highlighting the need for further studies on salinity management strategies for turbot aquaculture.

Growth Performance and Flesh Quality of Sea Bass (Dicentrarchus labrax) Fed with Diets Containing Olive Oil in Partial Replacement of Fish Oil-With or Without Supplementation with Rosmarinus officinalis L. Essential Oil

This study aimed to investigate the effects of using olive oil (OO) in a partial replacement of fish oil (FO), with or without supplementation with rosemary essential oil (RO), on the growth performances and flesh quality traits of farmed Dicentrarchus labrax. Sea bass were fed with the experimental diets for 200 days; afterwards, they were caught and stored in ice (0-2 °C) for up to 17 days. The specific growth rate (SGR) and feed conversion rate (FCR) were calculated. Fillets were analyzed for physical features, chemical composition, fatty acid profile, and malondialdehyde (MDA) concentration on days 0, 5, 10, and 17 of storage. The fillets were assessed for sensory properties according to the QIM and Torry Scheme methods. No statistical differences between groups were found for the final average body weight, SGR, FCR and the flesh chemical composition. Supplementation with RO reduced (p < 0.05) MDA concentration, thus improving the shelf life of fish by up to 10 days. The sensory score (QIM) increased linearly (p < 0.05) with storage time; for cooked fillet, the Torry Scheme score decreased (p < 0.05) with storage time. The economic analysis of feed cost has proven the feasibility of using olive oil as local feed ingredient in the partial replacement of fish oil.

Untargeted LC-MS metabolomics reveals the metabolic responses in the Eriocheir sinensis gills exposed to salinity and alkalinity stress

In recent years, saline-alkaline aquaculture development has become an important measure for China to expand its fishery development space to ensure food safety. Previous studies have verified that salinity and alkalinity positively influence the quality of Chinese mitten crabs (Eriocheir sinensis). However, the regulatory mechanism of E. sinensis endures saline-alkaline stress which remains obscure. This study investigated the metabolic changes in puberty-molting E. sinensis gills exposed to freshwater (FW), sodium chloride salinity of 5 ppt (SW), and carbonate alkalinity 10.00 mmol/L (AW) for 50 days using untargeted liquid chromatography-mass spectrometry metabolomics (LC-MS). A total of 5802 (positive-ion mode) and 6520 (negative-ion mode) peaks were extracted by LC-MS, respectively. A total of 188 (50 upregulated and 138 downregulated), 141 (94 upregulated and 47 downregulated), and 130 (87 upregulated and 43 downregulated) significantly regulated metabolites (SRMs) were observed in the FW-SW, FW-AW, and SW-AW treatments, respectively, wherein 42 generic SRMs were also found by Venn diagram analysis. Seven of the top 10 SRMs with the highest (variable importance in projection) VIP values were similarly identified in FW-SW and SW-AW. Integrated analysis of key metabolic pathways revealed glycerophospholipid, choline in cancer, phenylalanine, and butanoate metabolism. Overall, significant differences were observed in the metabolites and key metabolic pathways of E. sinensis gill exposed to salinity and alkalinity stress. These results will be helpful in understanding the environmental adaptability of aquatic crustaceans to saline-alkaline water.

The balance of n-6 and n-3 fatty acids in canine, feline, and equine nutrition: exploring sources and the significance of alpha-linolenic acid

Both n-6 and n-3 fatty acids (FA) have numerous significant physiological roles for mammals. The interplay between these families of FA is of interest in companion animal nutrition due to the influence of the n-6:n-3 FA ratio on the modulation of the inflammatory response in disease management and treatment. As both human and animal diets have shifted to greater consumption of vegetable oils rich in n-6 FA, the supplementation of n-3 FA to canine, feline, and equine diets has been advocated for. Although fish oils are commonly added to supply the long-chain n-3 FA eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), a heavy reliance on this ingredient by the human, pet food, and equine supplement industries is not environmentally sustainable. Instead, sustainable sourcing of plant-based oils rich in n-3 α-linolenic acid (ALA), such as flaxseed and camelina oils, emerges as a viable option to support an optimal n-6:n-3 FA ratio. Moreover, ALA may offer health benefits that extend beyond its role as a precursor for endogenous EPA and DHA production. The following review underlines the metabolism and recommendations of n-6 and n-3 FA for dogs, cats, and horses and the ratio between them in promoting optimal health and inflammation management. Additionally, insights into both marine and plant-based n-3 FA sources will be discussed, along with the commercial practicality of using plant oils rich in ALA for the provision of n-3 FA to companion animals.

Effects of different temperatures on seawater acclimation in rainbow trout Oncorhynchus mykiss: osmoregulation and branchial phospholipid fatty acid composition

This study aimed to investigate the effects of different temperatures on seawater acclimation in rainbow trout (Oncorhynchus mykiss), in terms of growth performance, osmoregulatory capacity, and branchial phospholipid fatty acid (PLFA) composition. The fish (initial weight, 94.73 g) were reared at 9, 12.5, and 16 °C for 28 days, then acclimated to seawater, and subsequently reared for 14 days. Sampling points were on the last day in freshwater, and the 1st, 4th, 7th, and 14th days after the salinity reached 30. The results showed the final weight, percent weight gain, and specific growth rate of rainbow trout at 12.5 °C were significantly higher than those at 9 °C, while the thermal growth coefficient at 16 °C was significantly lower than that in other treatments. The branchial PLFA composition in rainbow trout changed more rapidly at 9 and 12.5 °C than at 16 °C. The branchial PLFA composition was significantly affected by temperature and salinity and their interaction. The polyunsaturated fatty acid content of phospholipids in the gill at 9 and 12.5 °C was significantly higher than those at 16 °C. Low temperature (9 °C) and seawater acclimation significantly increased the degree of unsaturation of membrane, enhancing membrane fluidity, which is related to Na⁺-K⁺ ATPase activity. Responses of plasma ion, Na⁺-K⁺ ATPase activity, and plasma glucose followed a similar pattern at different temperatures. Overall, the study suggests that 12.5 °C is the ideal temperature for seawater acclimation in rainbow trout.

Seawater Culture Increases Omega-3 Long-Chain Polyunsaturated Fatty Acids (N-3 LC-PUFA) Levels in Japanese Sea Bass (Lateolabrax japonicus), Probably by Upregulating Elovl5

The fatty acid compositions of the fish muscle and liver are substantially affected by rearing environment. However, the mechanisms underlying this effect have not been thoroughly described. In this study, we investigated the effects of different culture patterns, i.e., marine cage culture and freshwater pond culture, on long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis in an aquaculturally important fish, the Japanese sea bass (Lateolabrax japonicus). Fish were obtained from two commercial farms in the Guangdong province, one of which raises Japanese sea bass in freshwater, while the other cultures sea bass in marine cages. Fish were fed the same commercial diet. We found that omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) levels in the livers and muscles of the marine cage cultured fish were significantly higher than those in the livers and muscles of the freshwater pond cultured fish. Quantitative real-time PCRs indicated that fatty acid desaturase 2 (FADS2) transcript abundance was significantly lower in the livers of the marine cage reared fish as compared to the freshwater pond reared fish, but that fatty acid elongase 5 (Elovl5) transcript abundance was significantly higher. Consistent with this, two of the 28 CpG loci in the FADS2 promoter region were heavily methylated in the marine cage cultured fish, but were only slightly methylated in freshwater pond cultured fish (n = 5 per group). Although the Elovl5 promoter was less methylated in the marine cage reared fish as compared to the freshwater pond reared fish, this difference was not significant. Thus, our results might indicate that Elovl5, not FADS2, plays an important role in the enhancing LC-PUFA synthesis in marine cage cultures.

Transcriptomic response to three osmotic stresses in gills of hybrid tilapia (Oreochromis mossambicus female × O. urolepis hornorum male)

Background

Osmotic stress is a widespread phenomenon in aquatic animal. The ability to cope with salinity stress and alkaline stress is quite important for the survival of aquatic species under natural conditions. Tilapia is an important commercial euryhaline fish species. What’s more tilapia is a good experimental material for osmotic stress regulation research, but the molecular regulation mechanism underlying different osmotic pressure of tilapia is still unexplored.

Results

To elucidate the osmoregulation strategy behind its hyper salinity, alkalinity and salinity-alkalinity stress of tilapia, the transcriptomes of gills in hybrid tilapia (Oreochromis mossambicus ♀ × O. urolepis hornorum ♂) under salinity stress (S: 25‰), alkalinity stress(A: 4‰) and salinity-alkalinity stress (SA: S: 15‰, A: 4‰) were sequenced using deep-sequencing platform Illumina/HiSeq-2000 and differential expression genes (DEGs) were identified. A total of 1958, 1472 and 1315 upregulated and 1824, 1940 and 1735 downregulated genes (P-value < 0.05) were identified in the salt stress, alkali stress and saline-alkali stress groups, respectively, compared with those in the control group. Furthermore, Kyoto Encyclopedia of Genes and Genomes pathway analyses were conducted in the significant different expression genes. In all significant DEGs, some of the typical genes involved in osmoregulation, including carbonic anhydrase (CA), calcium/calmodulin-dependent protein kinase (CaM kinase) II (CAMK2), aquaporin-1(AQP1), sodium bicarbonate cotransporter (SLC4A4/NBC1), chloride channel 2(CLCN2), sodium/potassium/chloride transporter (SLC12A2 / NKCC1) and other osmoregulation genes were also identified. RNA-seq results were validated with quantitative real-time PCR (qPCR), the 17 random selected genes showed a consistent direction in both RNA-Seq and qPCR analysis, demonstrated that the results of RNA-seq were reliable.

Conclusions

The present results would be helpful to elucidate the osmoregulation mechanism of aquatic animals adapting to saline-alkali challenge. This study provides a global overview of gene expression patterns and pathways that related to osmoregulation in hybrid tilapia, and could contribute to a better understanding of the molecular regulation mechanism in different osmotic stresses.

Season and Cooking May Alter Fatty Acids Profile of Polar Lipids from Blue-Back Fish

Polar lipids (PoL) represent a new promising dietary approach in the prevention and treatment of many human diseases, due to their potential nutritional value and unique biophysical properties. This study investigates the effects of catching season and oven baking on the fatty acid profiles (FAP) of PoL in four species of blue-back fish widely present in the North Adriatic Sea: anchovy (Engraulis encrasicholus), sardine (Sardina pilchardus), sprat (Sprattus sprattus), and horse mackerel (Trachurus trachurus). PoL levels (427-652 mg/100 g flesh) varied among the four species, with no significant seasonal variations within species. FAP of raw fillets were particularly high in polyunsaturated fatty acid (PUFA), especially docosahexaenoic acid (DHA) and EPA; total PUFA was constant in all species throughout the year, while long-chain n-3 polyunsaturated fatty acid (n-3 PUFA) rose in spring (except in sprat), especially due to the contribution of DHA. The FAP response for PoL to oven baking was species-specific and, among n-3 PUFA, DHA exhibited the greatest heat resistance; the influence of oven baking on FAP was found to be correlated with the catching season, especially for anchovy and sardine, while sprat PoL were not affected by cooking processes. The four species analyzed in this study presented very low n-6/n-3 fatty acid ratios and highly favorable nutritional indices, emphasizing their PoL qualities and promoting their role in increasing human n-3 PUFA intake. The four species can be considered as superior sources of n-3 PUFA and can be employed as supplements in functional food manufacturing and in pharmaceutical and cosmetic industries.

Biochemical impacts in adult and juvenile farmed European seabass and gilthead seabream from semi-intensive aquaculture of southern European estuarine systems

The nutritional value and developmental variations of cultured fish were assessed for European seabass and gilthead seabream specimens reared in semi-intensive aquaculture systems in two Portuguese estuaries. Quantification of total protein and of carbohydrate and fatty acid profiles was carried out to determine differences between the composition of the same species in two development stages reared in four distinct farms. A significant influence of the rearing site on the nutritional composition of the same species was found for adult European seabass regarding saturated, monounsaturated and highly unsaturated fatty acids contents, both between estuaries and within each estuary. In gilthead seabream, saturated, monounsaturated, polyunsaturated and highly unsaturated fatty acids content were also influenced by the rearing site. Carbohydrate analysis showed a significant influence of the rearing site on free sugar and polysaccharide content in fish of both species, and there was no influence on the species' protein content. Differences in fatty acid and carbohydrate content among juvenile and adult stages were found for all the groups studied. The present study supported the existing evidence that semi-intensive rearing systems are subjected to the variability of extrinsic factors in the rearing sites, influencing the nutritional value of the same species, namely regarding lipid and carbohydrate profiles, depending on the production site. From a consumer's perspective, such differences may come as a disadvantage of the rearing method, as it is expected for a product to provide equal nutritional properties and benefits regardless its origin, especially within the same country.

Impact of the replacement of dietary fish oil by animal fats and environmental salinity on the metabolic response of European Seabass (Dicentrarchus labrax)

The replacement of fish oil (FO) with other lipid sources (e.g. animal fats, AF) in aquafeeds improves the sustainability of aquaculture, even though alternatives have different fatty acid (FA) profiles. FO contains a higher proportion of long-chain polyunsaturated fatty acids (LC-PUFAs) than AF. LC-PUFAs have key physiological roles, despite limited biosynthetic capacity in marine fish. Therefore, replacing FO in feeds may limit physiological responses when fish face environmental challenges such as an acute change in salinity. To test this hypothesis, juvenile seabass (62.6 ± 1.6 g, 50 fish/ 500 L tank) were fed three different isoproteic and isolipidic diets in which the replacement levels of FO by AF varied (0%, 75% or 100% AF). Fish were fed the experimental diets at 2% their body weight (BW) daily for 85 days (20.0 ± 1.0 °C; 35‰). Thereafter, half of the fish were transferred to tanks at 15‰ or 35‰ salinity and sampled at 24 h and 72 h. Plasma osmolality, Na⁺, glucose, cholesterol and lactate levels were altered by the changing salinity, although cortisol remained unchanged. Standard metabolic rate was similar irrespective of the experimental factors. However, maximal metabolic rate decreased by 4-10% in fish subjected to a 15‰ salinity. Intestinal chymotrypsin activity was modified by the diet, with this digestive enzyme along with trypsin showing a two-fold increase in activity at 15‰ salinity. Hepatic lipid peroxidation (LPO) showed a ~1.4-fold increase at 15‰ salinity. Additionally, LPO and glutathione reductase activity were ~1.6-fold higher in fish fed the FO diet. Citrate synthase activity in gills was increased in fish fed the 100% AF diet. Therefore, both dietary replacement of FO by AF and environmental salinity have an impact on the metabolic response of seabass, although interactions between both factors (diet and salinity) are negligible in the metabolic parameters investigated. The results are relevant to the aquaculture industry considering the potential usage of AF to replace FO in aquafeeds and because of the variations in salinity experienced by fish cultured in transitional waters.

Impact of dietary starch on extrahepatic tissue lipid metabolism in farmed European (Dicentrarchus labrax) and Asian seabass (Lates calcarifer)

In aquaculture, there is high interest in substituting marine-derived with vegetable-based ingredients as energy source. Farmed carnivorous fish under high carbohydrate diets tend to increase adiposity but it remains unclear if this happens by increased lipid retention/accumulation, promotion of lipogenic pathways, or both. In order to determine the response of extrahepatic tissue to dietary starch, European (Dicentrarchus labrax) and Asian (Lates calcarifer) seabass were fed a control (low starch; LS) or experimental (high starch; HS) diet, for at least 21 days and then transferred for 6 days to saltwater enriched with deuterated water ²H₂O. Incorporation of ²H-labelling follows well-defined metabolic steps, and analysis of triacylglycerols (TAG) ²H-enrichment by ²HNMR allowed evaluation of de novo lipogenesis (DNL) in muscle and visceral adipose tissue (VAT). Fractional synthetic rates for TAG-bound fatty acids and glycerol were quantified separately providing a detailed lipogenic profile. The FA profile differed substantially between muscle and VAT in both species, but their lipogenic fluxes revealed even greater differences. In European seabass, HS promoted DNL of TAG-bound FA, in muscle and VAT. High ²H-enrichment also found in muscle TAG-bound glycerol was indicative of its role on lipid cycling. In Asian seabass, HS had no effect on muscle FA composition and lipogenic flux, with no ²H-enriched TAG being detected. VAT on the other hand revealed a strong enhancement of DNL in HS-fed fish along with high TAG-bound glycerol cycling. This study consolidated the use of ²H₂O as tracer for fish lipid metabolism in different tissues, under different dietary conditions and suitable to use in different fish models.

Transcriptomic analysis reveal an efficient osmoregulatory system in Siberian sturgeon Acipenser baeri in response to salinity stress

Sturgeons are euryhaline fish species that have developed specific mechanisms of osmotic and ion regulation to adapt to waters of varying salinity. For the aim to elucidate the osmoregulation strategy behind its high salinity tolerance of sturgeons, the transcriptomes of gills in Siberian sturgeon Acipenser baeri under salinity stress (30 ppt) were sequenced using deep-sequencing platform Illumina/HiSeq-2500 and differential expression genes (DEGs) were identified. A total of 167, 501, 278 clean reads were obtained and 280, 238 unigenes were composed of those clean reads with the mean length of 520nt, and the N50 of 630 bp. Unigenes Sequence alignment was implemented via KEGG, KOG, NT, NR, PFAM, Swiss-Prot, and GO databases. 62, 242 unigenes (22.21%) were annoated in at least one database. 11380 significantly differentially expressed unigenes were found, 6969 of which were up-regulated and 4411 were down-regulated by salinity stress. Amongst the top 20 KEGG pathways with the most amount of annotation sequences, some pathways such as glycerophospholipid metabolism, fatty-acid biosynthesis, glycolysis/gluconeogenesis, oxidative phosphorylation have been comprehensively proved to be relevant to osmoregulation. Despite of these, three possible osmoregulation-related signaling pathways as lipid metabolism related pathways, tight junction pathway and thyroid hormone signaling pathway have been widely analyzed in the current study. In all DEGs, some of the typical genes involved in osmoregulation, including calcium-transporting ATPase 4 (ATP2B4), Na⁺/K⁺-ATPase alpha subunit (α-NKA), potassium-transporting ATPase alpha chain 1 (ATP4A) and Ras GTPase-activating protein (RasGAP) etc were also identified. RNA-seq results were validated with quantitative real-time PCR (qPCR), the 12 selected genes showed a consistent direction in both DGE library and qPCR analysis, proving that the RNA-seq results are reliable. The present results would be helpful to elucidate the osmoregulation mechanism of aquatic animals adapting to salinity challenge.

Responses of blood biochemistry, fatty acid composition and expression of microRNAs to heat stress in genetically improved farmed tilapia (Oreochromis niloticus)

We investigated the effects of heat stress on genetically improved farmed tilapia, focusing on metabolic and immune responses. Differences in blood parameters, serum biochemistry, muscle fatty acid composition, and microRNA (miRNA) expression were analyzed in fish under heat stress. Fish were exposed to heat stress at 35 °C and sampled at 0, 6, 12, 24, and 48 h after exposure and compared with a control group maintained at 28 °C. The results showed that red and white blood cell counts, hemoglobin levels, and hematocrit values tended to increase (P < 0.05) and reached their maximum levels after 24 h, then declined. Acute heat stress enhanced serum glucose, total protein, and total cholesterol levels, and muscle fatty acid components were also altered. Serum alanine aminotransferase (ALT) activity was significantly increased after heat stress for 6 and 12 h. Polyunsaturated fatty acids levels were increased after heat stress for 12 and 24 h, whereas levels of monounsaturated fatty acids decreased in response to heat stress. Expression of hepatic miR-1 and miR-122 was significantly upregulated, and expression of miR-10c was significantly increased (P < 0.05) only after heat stress for 48 h. Acute heat stress altered metabolism closely related to the immune system and the liver of tilapia. These findings contribute to a theoretical framework for tilapia breeding at high temperatures.

Phospholipids of Animal and Marine Origin: Structure, Function, and Anti-Inflammatory Properties

In this review paper, the latest literature on the functional properties of phospholipids in relation to inflammation and inflammation-related disorders has been critically appraised and evaluated. The paper is divided into three sections: Section 1 presents an overview of the relationship between structures and biological activities (pro-inflammatory or anti-inflammatory) of several phospholipids with respect to inflammation. Section 2 and Section 3 are dedicated to the structures, functions, compositions and anti-inflammatory properties of dietary phospholipids from animal and marine sources. Most of the dietary phospholipids of animal origin come from meat, egg and dairy products. To date, there is very limited work published on meat phospholipids, undoubtedly due to the negative perception that meat consumption is an unhealthy option because of its putative associations with several chronic diseases. These assumptions are addressed with respect to the phospholipid composition of meat products. Recent research trends indicate that dairy phospholipids possess anti-inflammatory properties, which has led to an increased interest into their molecular structures and reputed health benefits. Finally, the structural composition of phospholipids of marine origin is discussed. Extensive research has been published in relation to ω-3 polyunsaturated fatty acids (PUFAs) and inflammation, however this research has recently come under scrutiny and has proved to be unreliable and controversial in terms of the therapeutic effects of ω-3 PUFA, which are generally in the form of triglycerides and esters. Therefore, this review focuses on recent publications concerning marine phospholipids and their structural composition and related health benefits. Finally, the strong nutritional value of dietary phospholipids are highlighted with respect to marine and animal origin and avenues for future research are discussed.

Changes in Plasma and Tissue Long-Chain Polyunsaturated Fatty Acid (LC-PUFA) Content in the Eel Anguilla japonica After External and Internal Osmotic Stress

We investigated the effect of external and internal osmotic stress on the profile of long-chain polyunsaturated fatty acids (LC-PUFA) in euryhaline eels Anguilla japonica. Freshwater (FW) fish were transferred to seawater (SW) for external osmotic stress or subjected to internal stress through injection with hypertonic saline. FW eels injected with isotonic saline served as controls. Plasma osmolality, Na⁺ concentration, and gill Na⁺/K⁺ -ATPase activity increased, but hematocrit decreased compared with controls in eels exposed to external or internal osmotic stress. The expression of two major transporter genes for SW adaptation, the Na⁺ -K⁺ -2Cl - co-transporter 1a (NKCC1a) in the gill and NKCC2b in the intestine, was up-regulated only in SW-transferred eels, suggesting a direct impact of SW on the gill and intestine via SW ingestion. Total LC-PUFA contents and DHA (22:6 n-3) increased in the gill and liver of SW-transferred eels and in the intestine of hypertonic saline-injected eels. However, total LC-PUFA content in plasma decreased after both external and internal osmotic stimuli. In contrast, the gene expression of two key enzymes involved in the LC-PUFA biosynthesis, Δ6 fatty acid desaturase and elongase, did not change in the gill, intestine and liver of osmotically stressed eels. These results indicate that LC-PUFA is possibly involved in osmoregulation and the increased LC-PUFA contents of osmoregulatory organs might be a result of LC-PUFA transport via circulation, rather than through de novo biosynthesis.

Transcriptional changes in Atlantic salmon (Salmo salar) after embryonic exposure to road salt

Road salt is extensively used as a deicing chemical in road maintenance during winter and has in certain areas of the world led to density stratifications in lakes and ponds, and adversely impacted aquatic organisms in the recipients of the road run-off. Aquatic vertebrates such as fish have been particularly sensitive during fertilisation, as the fertilisation of eggs involves rapid uptake of the surrounding water, reduction in egg swelling and in ovo exposure to high road salt concentrations. The present study aimed to identify the persistent molecular changes occurring in Atlantic salmon (Salmo salar) eggs after 24h exposure to high concentrations (5000 mg/L) of road salt at fertilisation. The global transcriptional changes were monitored by a 60k salmonid microarray at the eyed egg stage (cleavage stage, 255 degree days after fertilisation) and identified a high number of transcripts being differentially regulated. Functional enrichment, pathway and gene-gene interaction analysis identified that the differentially expressed genes (DEGs) were mainly associated with toxiciologically relevant processes involved in osmoregulation, ionregulation, oxidative stress, metabolism (energy turnover), renal function and developmental in the embryos. Quantitative rtPCR analysis of selected biomarkers, identified by global transcriptomics, were monitored in the eggs for an extended range of road salt concentrations (0, 50, 100, 500 and 5000 mg/L) and revealed a positive concentration-dependent increase in cypa14, a gene involved in lipid turnover and renal function, and nav1, a gene involved in neuraxonal development. Biomarkers for osmoregulatory responses such as atp1a2, the gene encoding the main sodium/potassium ATP-fueled transporter for chloride ions, and txdc9, a gene involved in regulation of cell redox homeostasis (oxidative stress), displayed apparent concentration-dependency with exposure, although large variance in the control group precluded robust statistical discrimination between the groups. A No Transcriptional Effect Level (NOTEL) of 50mg/L road salt was found to be several orders of magnitude lower than the adverse effects documented in developing fish embryos elsewhere, albeit at concentrations realistic in lotic systems receiving run-off from road salt. It remains to be determined whether these transcriptional changes may cause adverse effects in fish at ecologically relevant exposure concentrations of road salt.

Changes in the physiological parameters, fatty acid metabolism, and SCD activity and expression in juvenile GIFT tilapia (Oreochromis niloticus) reared at three different temperatures

We evaluated the effects of rearing temperature on the composition of fatty acids and stearoyl-CoA desaturase (SCD) activity and gene expression in GIFT (genetically improved farmed tilapia) tilapia. Three triplicate groups of fish were reared for 40 days at 22, 28, or 34 °C. At the end of the trial, the final body weight of juveniles reared at 28 °C was higher than that of fish reared at 22 or 34 °C. Feed intake, feed efficiency, and the protein efficiency ratio were also higher at 28 °C. The fatty acid composition of muscle tissue differed significantly (P < 0.05) among the treatment groups. The content of SFA decreased with decreasing temperature, whereas the UFA content increased. We observed high levels of PUFA, particularly n-3 PUFAs, in fish reared at the lower temperature. Rearing at low temperature significantly (P < 0.05) increased the expression and activity of the SCD gene. Increased SCD activity and gene expression can increase the biosynthesis of MUFAs in GIFT tilapia muscle. Additionally, cold acclimation can decrease the content of TC and TG in GIFT tilapia, which can help increase cold tolerance.

FemaleLeuciscus lepidusMay Be a New Alternative for Fish Oil Supplements

The proximate composition of male and femaleLeuciscus lepidusin Beyşehir Lake was investigated. The fatty acid profiles of total lipid, phospholipid, and triacylglycerol in muscle and liver of male and femaleL. lepiduswere evaluated by gas chromatography. Proximate analyses showed that meat of male and femaleL. lepidushad 15.13 ± 0.04 and 18.75 ± 0.11% fat, 20.42 ± 0.45 and 22.21 ± 0.56% protein, 65.47 ± 1.37 and 61.28 ± 1.03% moisture, and 1.51 ± 0.05 and 1.50 ± 0.03% ash, respectively. The percentage of total saturated fatty acids was higher in liver than in muscle, whereas the total polyunsaturated fatty acid (PUFA) content was the lowest in all fatty acid profiles. The phospholipids contained more PUFAs than triacylglycerol. Analysis of variance indicated significant differences (P<0.05) between male (47.51%) and female (49.98%) muscle PUFAs in total lipid. The proportion of omega 3 (ω3) to omega 6 (ω6) fatty acids of total lipid was 3.15 in male and 3.68 in female. The ratio is an important indicator for comparing the value of fish oil. Therefore, it was concluded thatL. lepiduswas considered to be a high quality product for healthy food choice. Additionally, femaleL. lepidusmay especially be used to produce fish oil supplements from freshwater fish combined with vegetable oils.

Effect of salinity on the biosynthesis of n-3 long-chain polyunsaturated fatty acids in silverside Chirostoma estor

The genus Chirostoma (silversides) belongs to the family Atherinopsidae, which contains around 150 species, most of which are marine. However, Mexican silverside (Chirostoma estor) is one of the few representatives of freshwater atherinopsids and is only found in some lakes of the Mexican Central Plateau. However, studies have shown that C. estor has improved survival, growth, and development when cultured in water conditions with increased salinity. In addition, C. estor displays an unusual fatty acid composition for a freshwater fish with high docosahexaenoic acid (DHA)/ eicosapentaenoic acid (EPA) ratios. Freshwater and marine fish species display very different essential fatty acid metabolism and requirements, and so the present study investigated long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis to determine the capacity of C. estor for endogenous production of EPA and DHA, and the effect that salinity has on these pathways. Briefly, C. estor were maintained at three salinities (0, 5, and 15 ppt), and the metabolism of ¹⁴C-labeled 18:3n-3 was determined in isolated hepatocyte and enterocyte cells. The results showed that C. estor has the capacity for endogenous biosynthesis of LC-PUFA from 18-carbon fatty acid precursors, but that the pathway was essentially only active in saline conditions with virtually no activity in cells isolated from fish grown in freshwater. The activity of the LC-PUFA biosynthesis pathway was also higher in cells isolated from fish at 15 ppt compared with fish at 5 ppt. The activity was around fivefold higher in hepatocytes compared with enterocytes; although the majority of 18:3n-3 was converted to 18:4n-3 and 20:4n-3 in hepatocytes, the proportions of 18:3n-3 converted to EPA and DHA were higher in enterocytes. The data were consistent with the hypothesis that conversion of EPA to DHA could contribute, at least in part, to the generally high DHA/EPA ratios observed in the tissue lipids of C. estor.

Differences in muscle cellularity and flesh quality between wild and farmed Coilia nasus (Engraulidae)

BACKGROUND

Populations of Coilia nasus, an anadromous fish, have declined dramatically in the Yangtze River estuary and its associated lakes owing to excessive fishing and changes in aquatic ecology. Recently, the success of artificial breeding programmes and advanced methods of propagation have allowed great increases in production of this species. Thus, to gain a better understanding of the flesh quality of C. nasus, muscle cellularity and quality parameters of the flesh were studied in wild and farmed specimens.

RESULTS

Muscle cellularity was different between wild and farmed fish. Muscle fibre density was significantly higher in farmed specimens, while muscle fibre diameter was higher in wild specimens. Farmed fish had higher moisture, hydroxyproline and collagen contents and a lower fat content compared with wild fish. No significant differences in textural parameters were found between the two groups. Saturated (SFA), polyunsaturated (PUFA) and total n-6 fatty acid contents were significantly higher in farmed fish, but monounsaturated fatty acid (MUPA) content was higher in wild fish.

CONCLUSION

The variation in the studied parameters determined significant differences in the flesh quality of wild and farmed C. nasus. Depending on muscle cellularity and fatty acid composition, farmed fish could be more suitable for human consumption than wild fish.

Seasonal changes in composition, fatty acid, cholesterol and mineral content of six highly commercial fish species of Greece

Changes in lipid, protein, ash and moisture, quantitative distribution of fatty acids, cholesterol and mineral content (Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni and Zn) of six common fish species from Greece were studied. The proximate composition of all samples was significantly influenced by the fishing period, even the cultured ones. The sum of C20:5ω–3 and C22:6ω–3 ranged from 1.18 to 2.76 for sardine, from 0.37 to 1.99 for bogue, from 1.1 to 1.52 for mackerel, from 1.23 to 1.46 for sea bass, from 1.00 to 1.24 for trout and from 0.26 to 0.45 g/100 g edible portion for hake samples. Besides the ratio of ω–3/ω–6 polyunsaturated fatty acids ranged from 6.80 to 19.00 for the wild fish samples and from 1.01 to 3.67 for the cultured ones. Cholesterol of sardine, bogue, mackerel, trout and sea bass ranged from 37 up to 76 mg/100 g edible flesh, while it was varied from 72 to 124 mg/100 g in the flesh of hake. The concentration of minerals was detected at acceptable levels. All fish samples seemed to be quite good sources of Mg, Zn and Fe. Co was not detected in the samples studied.

Fatty acid composition of the amphipod Dikerogammarus villosus: feeding strategies and trophic links

Fatty acid (FA) compositions were determined for the invader amphipod Dikerogammarus villosus collected from July to September 2002, in an overheated, high-conductivity dammed reservoir in north-eastern France. Predominant fatty acids were the polyunsaturated fatty acids (PUFA): eicosapentaenoic acid (EPA), linoleic acid (LA), arachidonic acid (ARA), linolenic acid (LNA) together with the monounsaturated fatty acid 18:1omega9 and the saturated fatty acid 16:0. FA markers indicated that available food was constituted of incompletely degraded phytodetritus and terrestrial inputs, as well as animal remains. PUFA contents depended on the diet and the capacity of animals to desaturate and elongate LNA and LA in long chain PUFA as EPA and ARA respectively. Based on their FA compositions, we showed that gammarids represent naturally-occurring freshwater sources of essential PUFA, and could play a fundamental role in pelagic-benthic coupling and energy recycling in the ecosystem. The complexity of the feeding strategies of D. villosus--detritivorous, omnivorous, carnivorous--makes this species efficient at exploiting different components of the available food and may be a key factor in its high invasive success.

Adaptive branchial mechanisms in the sturgeon Acipenser naccarii during acclimation to saltwater

Variations of Na(+)/K(+)-ATPase activity and fatty-acid composition in the gills of the sturgeon Acipenser naccarii subjected to progressive acclimation to full seawater (35 ppt) were determined in relation to the hypo-osmoregulatory capacity of this species in the hyperosmotic medium. Blood samples were taken and gills arches were removed at intermediate salinity levels between 0 and 35 ppt and after 20 days at constant salinity (35 ppt). Plasma osmolality and Na(+)/K(+)-ATPase activity increased significantly with growing environmental salinity. Total saturated fatty acids (SFAs) decreased, while total polyunsaturated fatty acids (PUFAs) increased significantly with increasing salinity due mainly to changes in n-3 PUFAs (20:5n-3 and 22:6n-3). The n-3/n-6 ratio increased significantly during the acclimation process. The results show a direct relationship between salinity, increased gill Na(+)/K(+)-ATPase activity and ultrastructural changes of the gill chloride cells. Changes in the fatty-acid composition in gills of A. naccarii during progressive acclimation to full seawater suggest that variations of gill fatty acids may also have a role in osmoregulatory mechanisms.

Fat to the fire: the regulation of lipid oxidation with exercise and environmental stress

Lipids are an important fuel for submaximal aerobic exercise. The ways in which lipid oxidation is regulated during locomotion is an area of active investigation. Indeed, the integration between cellular regulation of lipid metabolism and whole-body exercise performance is a fascinating but often overlooked research area. Additionally, the interaction between environmental stress, exercise, and lipid oxidation has not been sufficiently examined. There are many functional and structural steps as fatty acids are mobilized, transported, and oxidized in working muscle, which may serve either as regulatory points for responding to acute or chronic stimuli or as raw material for natural selection. At the whole-animal level, the partitioning of lipids and carbohydrates across exercise intensities is remarkably similar among mammals, which suggests that there is conservation in regulatory mechanisms. Conversely, the proportions of circulatory and intramuscular fuels differ between species and across exercise intensities. Responses to acute and chronic environmental stress likely involve the interaction of genetic and nongenetic changes in the fatty acid pathway. Determining which of these factors help regulate the fatty acid pathway and what impact they have on whole-animal lipid oxidation and performance is an important area of future research. Using an integrative approach to complete the information loop from gene to physiological function provides the most powerful mode of analysis.