Reproductive behaviour and fertilized spawns in cultured Solea senegalensis broodstock co-housed with wild breeders during their juvenile stages.

The reproductive failure of Senegalese sole (Solea senegalensis) cultured males (reared entirely in captivity from egg through to adult) that do not participate in reproductive behaviours to fertilise spawns, results in a problem to achieve reproductive control in captivity. However, cohabitation with wild males has led to an increase in the involvement of cultured males in reproductive behaviour, although their contribution to fertilised spawning is still lower than that of wild breeders. This study aimed to examine the effect of different social conditions, on the reproductive behaviour and spawning success of cultured breeders over three reproductive seasons. Before starting this study, different social learning opportunities were provided to the breeders from the juvenile to the pubertal stages of the individuals. Behaviour and spawning were evaluated in four experimental groups of cultured breeders: two groups (W1 and W2) that prior to this study were reared during the juvenile stage with wild breeders that fertilized spawns, a Culture breeder group (CB) that was previously reared with cultured breeders that spawned unfertile eggs, and a negative control group (CN) that was reared in isolation from adult fish. During the three reproductive seasons, spawning was obtained from all groups. Generally, the first year had the highest egg production and the third year the lowest. However, fertilised eggs were only obtained from W1 in the first year. A total of eight fertilised spawns were collected with a fertilisation rate of 28.02 ± 13.80 % and a hatching rate of 15.04 ± 10.40 %. The mean number of larvae obtained per spawn was 7,683 ± 5,947 and the total number of larvae from all eight spawns was 61,468. The paternity analysis assigned 64.3 % of larvae to a single couple of breeders, while 34.3 % of larvae were not assigned to any single family, but inconclusively to more than three parents. The highest locomotor activity was observed in W1, while no significant differences were observed in the number of movements within W2, CB and CN. In all groups, during the peak of locomotor activity (19h00-20h00), the main reproductive behaviours observed were Rest the Head and Follow, while the Guardian behaviour was low and Coupled behaviour was only observed in W1. Over time, the reproductive behaviours decreased, except for Follow. The social learning opportunities provided by cohabitation with wild fish during juvenile stages prior to spawning in W1, increased activity and fertilised spawning. However, the number of successful spawns was low and over time stopped in association with a decrease in reproductive behaviour. This suggests that other mechanisms of behavioural learning could be involved in reproductive success, such as reproductive dominance, environmental conditions or hormonal interactions that could affect physiological processes in the reproduction of captive breeders.

Optimal dietary lipid levels alleviated adverse effects of high temperature on growth, lipid metabolism, antioxidant and immune responses in juvenile turbot (Scophthalmus maximus L.).

Fish physiological health is often negatively impacted by high-temperature environments and there are few studies on how dietary lipids affect fish growth and physiology when exposed to heat stress. The main objective of this research was to examine the impact of dietary lipid levels on growth and physiological status of juvenile turbot (Scophthalmus maximus L.) and determine if dietary lipid concentration could alleviate the possible adverse effects of heat stress. Five diets containing 6.81%, 9.35%, 12.03%, 14.74%, and 17.08% lipid, respectively, were formulated and fed to turbot (initial weight 5.13 ± 0.02 g) under high-temperature conditions (24.0-25.0 °C). Meanwhile, the diet with 12.03% lipid (considered by prior work to be an optimal dietary lipid level) was fed to turbot of the same size at normal temperature. Results suggested that, among the different dietary lipid levels under high-temperature conditions, fish fed the optimal lipid (12.03%) exhibited better growth compared to non-optimal lipid groups, as evidenced by higher weight gain and specific growth rate. Simultaneously, the optimal lipid diet may better maintain lipid homeostasis, as attested by lower liver and serum lipid, along with higher liver mRNA levels of lipolysis-related genes (pgc1α, lipin1, pparα, lpl and hl) and lower levels of synthesis-related genes (lxr, fas, scd1, pparγ, dgat1 and dgat2). Also, the optimal lipid diet might mitigate oxidative damage by improving antioxidant enzyme activity, decreasing malondialdehyde levels, and up-regulating oxidation-related genes (sod1, sod2, cat, gpx and ho-1). Furthermore, the optimal lipid may enhance fish immunity, as suggested by the decrease in serum glutamic-oxalacetic/pyruvic transaminase activities, down-regulation of pro-inflammatory genes and up-regulation of anti-inflammation genes. Correspondingly, the optimal lipid level suppressed MAPK signaling pathway via decreased phosphorylation levels of p38, JNK and ERK proteins in liver. In summary, the optimal dietary lipid level facilitated better growth and physiological status in turbot under thermal stress.

Bioinspired flatfish detection using electrical impedance measurements.

Bottom trawling for flatfish by means of tickler chains has a high ecological impact due to the continuous seabed disturbance, low selectivity and high fuel costs. This issue could be significantly mitigated by using localized startle stimuli, triggered by a detection system that selectively targets flatfishes of landable size. Flatfish, however, constitute a significant challenge for remote detection, due to their low optical and acoustical signatures. Some species of predatory fish feeding on flatfish overcome this issue by using electroreception to localize they prey, even if it is buried in bottom sediments. We take this phenomenon as an inspiration in an attempt to develop a biomimetic remote fish detection technique based on electrical impedance measurements. We constructed a detection system including a set of electrodes and a low-cost analog front-end. The electrodes were mounted on a dedicated frame and dragged above a layer of sand inside a tank with sea water and several common sole (Solea solea). An underwater camera was used to acquire video recordings synchronized with impedance data for reference. We demonstrate that fish presence below the electrodes manifests itself by changes in the measured resistance and reactance values. This phenomenon occurs even if the fish is covered with a layer of sand. The results demonstrate the potential of bioinspired remote flatfish detection, which could be highly useful for monitoring or targeted stimulation.

Quantifying spatio-temporal consistency in the trophic ecology of two sympatric flatfishes.

Sympatric flatfish predators may partition their resources in coastal environments to reduce competition and maximise foraging efficiency. However, the degree of spatial and temporal consistency in their trophic ecology is not well understood because dietary studies tend to overlook the heterogeneity of consumed prey. Increasing the spatial and temporal scale of dietary analyses can thus help to resolve predator resource use. We applied a stomach content and multi-tissue (liver and muscle) stable isotope (δ13 C, δ15 N and δ34 S) approach to investigate the feeding habits of two co-occurring flatfish predators, common dab (Limanda limanda) and European plaice (Pleuronectes platessa), across four bays on the Northumberland coast (UK) over short (hours), medium (days) and long (months) temporal scales. Stomach content analyses showed spatial consistencies in predator resource use, whereas stable isotope mixing models revealed considerable inter-bay diet variability. Stomach contents also indicated high dietary overlap between L. limanda and P. platessa, while the stable isotope data yielded low to moderate levels of overlap, with cases of complete niche separation. Furthermore, individual specialisation metrics indicated consistently low levels of specialisation among conspecifics over time. We document changes in resource partitioning in space and time, reflecting diet switching in response to local and temporal fluctuations of patchily distributed prey. This study highlights how trophic tracers integrated at multiple temporal and spatial scales (within tens of kilometres) provide a more integrative approach for assessing the trophic ecology of sympatric predators in dynamic environments.

Genotype by Temperature Interaction for Plasma Physiological Indexes in Turbot (Scophthalmus maximus) under Acute Heat Stress─Exploring a Method for Screening Physiological Biomarkers of Nontoxic Stress in Aquatic Environments.

This paper presents a method for exploring the genetic mechanism underlying the plasma physiological indexes under heat stress in aquatic environments and for screening reliable stress biomarkers based on split-split-plot analysis (SSP), additive main effects and multiplicative interaction (AMMI) analysis, and genotype main effects and genotype × environment interaction (GGE) biplot analysis. The methodology developed was illustrated by applying it to a specific turbot heat stress case study. Five plasma physiological indexes (epinephrine, cortisol, alkaline phosphatase, superoxide dismutase, and blood glucose levels) were measured in turbot (Scophthalmus maximus) under acute heat stress at four temperatures (18, 21, 24, and 27 °C) for various exposure times (3, 6, 9, 12, 24, 48, and 72 h). The SSP analysis showed that exposure time and temperature × gene interactions had significant (P < 0.01) effects on the activity/content of turbot plasma physiological indexes. The AMMI analysis showed the following: (1) that at each exposure time, the genotype effect > the genotype × temperature interaction > the temperature effect; (2) that during the whole experiment, the change trend of the contribution of the genotype × temperature interactions was similar to that of the temperature effect, and the changing trends of the contributions of the genotype × temperature interaction and the genotype effect were clearly completely reversed; and (3) that the 3-24-h period was the key period for the changes in the physiological indexes due to acute heat stress. The GGE biplot analysis showed that blood glucose and cortisol levels were reliable biomarkers and could be used as early warning markers for numerical simulations of physiological behavior.

Identification of quantitative trait loci associated with upper temperature tolerance in turbot, Scophthalmus maximus.

Temperature tolerance is an important trait from both an economic and evolutionary perspective in fish. Because of difficulties with measurements, genome-wide selection using quantitative trait loci (QTLs) affecting Upper temperature tolerance may be an alternative for genetic improvement. Turbot Scophthalmus maximus (L.) is a cold-water marine fish with high economic value in Europe and Asia. The genetic bases of upper temperature tolerance (UTTs) traits have been rarely studied. In this study, we constructed a genetic linkage map of turbot using simple sequence repeats (SSRs) and single nucleotide polymorphism (SNP) markers. A total of 190 SSR and 8,123 SNP were assigned to 22 linkage groups (LGs) of a consensus map, which spanned 3,648.29 cM of the turbot genome, with an average interval of 0.44 cM. Moreover, we re-anchored genome sequences, allowing 93.8% physical sequences to be clustered into 22 turbot pseudo-chromosomes. A high synteny was observed between two assemblies from the literature. QTL mapping and validation analysis identified thirteen QLTs which are major effect QTLs, of these, 206 linked SNP loci, and two linked SSR loci were considered to have significant QTL effects. Association analysis for UTTs with 129 QTL markers was performed for different families, results showed that eight SNP loci were significantly correlated with UTT, which markers could be helpful in selecting thermal tolerant breeds of turbot. 1,363 gene sequences were genomically annotated, and 26 QTL markers were annotated. We believe these genes could be valuable candidates affecting high temperatures, providing valuable genomic resources for the study of genetic mechanisms regulating thermal stress. Similarly, they may be used in marker-assisted selection (MAS) programs to improve turbot performance.

Successful Spermatogonial Stem Cells Transplantation within Pleuronectiformes: First Breakthrough at inter-family Level in Marine Fish.

As a promising biotechnology, fish germ cell transplantation shows potentials in conservation germplasm resource, propagation of elite species, and generation of transgenic individuals. In this study, we successfully transplanted the Japanese flounder (P. olivaceus), summer flounder (P. dentatus), and turbot (S. maximus) spermatogonia into triploid Japanese flounder larvae, and achieved high transplantation efficiency of 100%, 75-95% and 33-50% by fluorescence tracking and molecular analysis, respectively. Eventually, donor-derived spermatozoa produced offspring by artificial insemination. We only found male and intersex chimeras in inter-family transplantations, while male and female chimeras in both intra-species and intra-genus transplantations. Moreover, the intersex chimeras could mature and produce turbot functional spermatozoa. We firstly realized inter-family transplantation in marine fish species. These results demonstrated successful spermatogonial stem cells transplantation within Pleuronectiformes, suggesting the germ cells migration, incorporation and maturation within order were conserved across a wide range of teleost species.

Effect of rearing density on nervous necrosis virus infection in Senegalese sole (Solea senegalensis).

Intensive fish farming at high densities results in a wide range of adverse consequences on fish welfare, including pathogen spreading, stress and increased mortality rates. In this work, we have assessed whether the survival of Senegalese sole infected with the nervous necrosis virus (NNV), a pathogen responsible for severe disease outbreaks, is affected by rearing density. Based on the different fish ratios per surface area (g cm-2 ) and water volume (g L-1 ), our research showed an earlier mortality onset in the tanks containing NNV-infected fish reared at medium density (MD: 0.071 g cm-2 /5 g L-1 ) and high density (HD: 0.142 g cm-2 /10 g L-1 ), as well as higher cumulative mortality values. However, transcription analysis of hsp70, gr1 and pepck genes, well-known stress biomarkers, seems to indicate that none of the challenged fish were under high stress conditions. NNV load was slightly higher both in dead and in sampled fish from MD and HD groups, and especially in the rearing water from these groups, where peaks in mortality seemed to correlate with increasing NNV load in the water. In conclusion, our results suggest that rearing NNV-infected Senegalese sole at high densities resulted in an earlier mortality onset and higher cumulative values and viral load.

Protective effects of glutamine against soy saponins-induced enteritis, tight junction disruption, oxidative damage and autophagy in the intestine of Scophthalmus maximus L.

Soy saponins, as thermo-stable anti-nutrients in soybean meal (SBM), are the primary causal agents of SBM-induced enteritis, which represents a well-documented pathologic alternation involving the distal intestines of various farmed fish. Our previous work showed that soy saponins might lead to SBM-induced enteritis, destroy tight junction structure and induce oxidative damage in juvenile turbot. Glutamine, as a conditionally essential amino acid, is an important substrate utilized for the growth of intestinal epithelial cells. An 8-week feeding trial was carried out to determine whether glutamine can attenuate the detrimental effects of soy saponins. Three isonitrogenous-isolipidic experimental diets were formulated as follows: (i) fish meal-based diet (FM), considered as control; (ii) FM + 10 g/kg soy saponins, SAP; and (iii) SAP + 15 g/kg glutamine, GLN. The results showed that dietary soy saponins significantly increased the gene expression levels of inflammatory markers (IL-1ß, IL-8 and TNF-α) and related signaling factors (NF-кB, AP-1, p38, JNK and ERK), which were remarkably attenuated by dietary glutamine. Compared to SAP group, GLN-fed fish exhibited significantly higher expression levels of tight junction genes (CLDN3, CLDN4, OCLN, Tricellulin and ZO-1). Glutamine supplementation in SAP diet markedly suppressed the production of reactive oxygen species, malondialdehyde and protein carbonyl, and enhanced the activities of antioxidant enzymes as well as the mRNA levels of HO-1, SOD, GPX and Nrf2. Furthermore, GLN-fed fish had a remarkably lower number of autophagosomes compared to SAP-fed fish. In conclusion, our study indicated that glutamine could reverse the harmful effects of soy saponins on intestinal inflammation, tight junction disruption and oxidative damage, via attenuation of NF-кB, AP-1 and MAPK pathways and activation of Nrf2 pathway. Glutamine may have the function of controlling autophaghic process within an appropriate level of encountering inflammation.

Daily rhythms of intestinal cholecystokinin and pancreatic proteases activity in Senegalese sole juveniles with diurnal and nocturnal feeding.

The influence of diurnal and nocturnal feeding on daily rhythms of gut levels of cholecystokinin (CCK) and the activity of two key pancreatic proteases, trypsin and chymotrypsin, were examined in juveniles of Senegalese sole (Solea senegalensis), a species with nocturnal habits. Four feeding protocols were performed: P1) One morning meal; P2) Six meals during the light period; P3) Six meals during the dark period; and P4) 12 meals during 24 h. Daily activity patterns of both proteases were remarkably similar and showed a high correlation in all the experimental protocols. In P1, daily patterns of CCK and digestive enzymes showed a single maximum. In P2, CCK levels exhibited two peaks. Digestive enzymes activities showed slightly delayed peaks compared to CCK, although their daily fluctuations were not significant. In P3, intestinal CCK concentration exhibited two peaks at the end of light and dark periods, but only the second one was significant. The first maximum level of chymotrypsin activity occurred 4 h after the first CCK peak, while the second one coincided with the second CCK peak. Fluctuations of trypsin activity were not significant. In P4, CCK concentration showed three small peaks. Digestive enzymes daily fluctuations were not significant, although they showed an inverted trend with respect to CCK. The daily pattern of the gut CCK content in our study is in agreement with the anorexigenic function of this hormone. Our results support the existence of a negative feedback regulatory loop between CCK and pancreatic proteolytic enzymes in Senegalese sole juveniles.

Heat stress-induced HSP90 expression is dependent on ERK and HSF1 activation in turbot (Scophthalmus maximus) kidney cells.

Mitogen-activated protein kinases (MAPKs) and heat shock proteins (HSPs) are ubiquitous proteins that are functional mediators in both normal and stressed states of the cell. In this study, we performed heat stress (37 °C) experiments on turbot kidney (TK) cells. Heat stress expression patterns of HSP90, as well as the expression and phosphorylation levels of extracellular-regulated signal kinases (ERKs) and the transcription factor HSF1 and c-Fos, were examined. The results show that heat stress activates ERK1/2 and HSF1, and induces HSP90 gene expression in TK cells. Inhibition of ERK activation attenuates heat stress-induced HSP90 gene expression. The double luciferase reporter gene experiment showed that HSF1 is an important transcription factor for heat-induced HSP90 gene expression. Likewise, c-Fos does not directly regulate the heat-induced expression of HSP90 in turbot kidney cells. To our knowledge, this is the first study to report a signaling pathway that regulates the heat shock response in turbot cells. Our results may facilitate an understanding of the underlying molecular mechanisms of the cellular stress response in marine fish.

Kisspeptin Influences the Reproductive Axis and Circulating Levels of microRNAs in Senegalese Sole.

Kisspeptin regulates puberty and reproduction onset, acting upstream of the brain-pituitary-gonad (HPG) axis. This study aimed to test a kisspeptin-based hormonal therapy on cultured Senegalese sole (G1) breeders, known to have reproductive dysfunctions. A single intramuscular injection of KISS2-10 decapeptide (250 µg/kg) was tested in females and males during the reproductive season, and gonad maturation, sperm motility, plasma levels of gonadotropins (Fsh and Lh) and sex steroids (11-ketotestosterone, testosterone and estradiol), as well as changes in small non-coding RNAs (sncRNAs) in plasma, were investigated. Fsh, Lh, and testosterone levels increased after kisspeptin injection in both sexes, while sperm analysis did not show differences between groups. Let7e, miR-199a-3p and miR-100-5p were differentially expressed in females, while miR-1-3p miRNA was up-regulated in kisspeptin-treated males. In silico prediction of mRNAs targeted by miRNAs revealed that kisspeptin treatment might affect paracellular transporters, regulate structural and functional polarity of cells, neural networks and intracellular trafficking in Senegalese sole females; also, DNA methylation and sphingolipid metabolism might be altered in kisspeptin-treated males. Results demonstrated that kisspeptin stimulated gonadotropin and testosterone secretion in both sexes and induced an unanticipated alteration of plasma miRNAs, opening new research venues to understand how this neuropeptide impacts in fish HPG axis.

Flatfishes colonised freshwater environments by acquisition of various DHA biosynthetic pathways.

The colonisation of freshwater environments by marine fishes has historically been considered a result of adaptation to low osmolality. However, most marine fishes cannot synthesise the physiologically indispensable fatty acid, docosahexaenoic acid (DHA), due to incomplete DHA biosynthetic pathways, which must be adapted to survive in freshwater environments where DHA is poor relative to marine environments. By analysing DHA biosynthetic pathways of one marine and three freshwater-dependent species from the flatfish family Achiridae, we revealed that functions of fatty acid metabolising enzymes have uniquely and independently evolved by multi-functionalisation or neofunctionalisation in each freshwater species, such that every functional combination of the enzymes has converged to generate complete and functional DHA biosynthetic pathways. Our results demonstrate the elaborate patchwork of fatty acid metabolism and the importance of acquiring DHA biosynthetic function in order for fish to cross the nutritional barrier at the mouth of rivers and colonise freshwater environments.

Unexpected deep-sea fish species on the Porcupine Bank (NE Atlantic): Biogeographical implications.

Four specimens corresponding to three rare deep-water fish species were caught on the Porcupine Bank (Northeast Atlantic) in September 2019. These catches include the new northernmost records of Azores rockling Gaidropsarus granti and deep-water dab Poecilopsetta beanii in the Atlantic Ocean and the second record of the latter species in its eastern zone. Three of the specimens were retained and their molecular identification also allowed the Cataetyx alleni DNA barcode to be obtained for the first time. The appearance of P. beanii, a West Atlantic species, in its eastern zone is discussed in relation to a possible phenomenon of transoceanic drift in the larval stage.

Comparative transcriptomic analysis reveals mechanisms of divergence in osmotic regulation of the turbot Scophthalmus maximus.

The turbot Scophthalmus maximus has evolved extensive physiological ability to adapt to multiple environmental salinities. The morphological changes of the kidney indicated the adaptability difference and similarity of turbot to salinity stress. Identify transcriptome-wide differences between low-salinity seawater (LSW, salinity 5)- and high-salinity seawater (HSW, salinity 50)-acclimated kidneys of turbot to decipher the osmotic regulation mechanism. We identified 688 differentially expressed genes (DEGs) in the LSW-acclimated kidneys and 2441 DEGs in the HSW-acclimated kidneys of turbot compared with seawater-acclimated kidneys, respectively. We investigated three patterns of gene regulation to salinity stress that involved in ion channels and transporters, functions of calcium regulation, organic osmolytes, energy demand, cell cycle regulation, and cell protection. Additionally, protein-protein interaction (PPI) analysis of DEGs suggested the presence of a frequent functional interaction pattern and that crucial genes in the PPI network are involved in hyper-osmotic regulation. Based on the analysis of comparative transcriptome data and related literature reports, we conclude that the mechanisms responsible for osmotic regulation and its divergence in turbot are related to various genes that are involved in canonical physiological functions. These findings provide insight into the divergence in osmoregulation of turbot and valuable information about osmoregulation mechanisms that will benefit other studies in this field.

Trophic transfer of trace elements in a euryhaline fish, the turbot Scophthalmus maximus: Contrasting effects of salinity on two essential elements.

Trace elements can be accumulated from coastal environment by aquatic organisms from their food and be transferred throughout the food webs. Studying the effects of salinity on the trophic transfer of trace elements in a euryhaline fish, able to deal with large variations in salinity, is therefore key to understand their dynamics in aquatic environments. In this context, we investigated the potential influence of salinity on the trophic transfer of two essential elements (Mn and Zn) in the euryhaline fish, the turbot Scophthalmus maximus using radiotracer techniques. After acclimation to three salinities (10, 25 and 38), turbots were fed with radiolabelled pellets (54Mn and 65Zn). Kinetic parameters of depuration were determined after a 21-d period and trophic transfer factors were calculated. Trophic transfer of Mn at the highest salinity was significantly lower than for the other conditions whereas salinity did not significantly influenced Zn trophic transfer. Differences in the processes involved in the regulation (homeostasis) of the two tested trace elements may explain the contrasting influence of seawater salinity for Mn and Zn.

Myo-inositol enhances the low-salinity tolerance of turbot (Scophthalmus maximus) by modulating cortisol synthesis.

Myo-inositol is a major intracellular osmolyte that can be accumulated to protect cells from a variety of stresses, including fluctuations in the osmolality of the environment, and cortisol is thought to be an osmotic hormone in teleost fish. In this study, dietary myo-inositol resulted in increased Na+-K+-ATPase activity and gene expression of partial ion channel genes and prolonged survival time of turbot (Scophthalmus maximus) under low salinity. The cortisol regulated by dietary myo-inositol also was correlated with these outcomes. The optimal concentrations of cortisol stimulated gill Na+-K+-ATPase activity and increased the expression of ion channel genes to enhance low salinity tolerance, as indicated by longer survival time under low salinity. When cortisol level was suppressed, myo-inositol failed to increase the survival time of turbot under low salinity, and strong correlations between cortisol concentration and Na+-K+-ATPase activity, expression of partial ion channel genes, and survival time of turbot were detected. These results showed that myo-inositol enhanced the low salinity tolerance of turbot by modulating cortisol synthesis.

Metabolic responses in Scophthalmus maximus kidney subjected to thermal stress.

Turbot (Scophthalmus maximus) is an economically important marine fish cultured in China. In this study, fish in the experimental group were exposed to four temperatures: 15, 20, 25 and 28 °C. Metabolomics analysis and quantitative real-time PCR were used to assess changes in metabolic profiling and gene expression associated with thermal stress. The results showed the levels of heat shock protein 70 (HSP70), heat shock protein 90 (HSP90), blood creatinine and cortisol in S. maximus were all significantly upregulated (P < 0.05), indicating a stress response at 25 °C or higher. Challenge with thermal stress significantly increased expression levels of succinate dehydrogenase (SDH), fructose-1, 6-bisphosphatase (FBPase), malate dehydrogenase (MDH), cytosolic phosphoenolpyruvate carboxykinase (cPEPCK), glucose-6-phosphatase (G6Pase) and aspartate aminotransferase (AST) (P < 0.05). However, there was no effect on the expression levels of lactate dehydrogenase (LDH), alanine aminotransferase (ALT) and mitochondrial phosphoenolpyruvate carboxykinase (mPEPCK). Moreover, high temperature decreased levels of glycogenic amino acids, including histidine, threonine, glutamine, phenylalanine, arginine, serine, tyrosine, methionine and isoleucine. These findings suggest a significant correlation between gene expression and regulation of carbohydrate and amino acid metabolism in heat-stressed S. maximus kidney. In addition, the maintenance of aerobic metabolism and activation of gluconeogenesis appeared to be a critical metabolic strategy in combating heat stress in turbot kidney.

Combined effects of high hydrostatic pressure and dispersed oil on the metabolism and the mortality of turbot hepatocytes (Scophthalmus maximus).

Since the DeepWater Horizon oil spill and the use at 1450 m depth of dispersant as a technical response, the need of relevant ecotoxicological data on deep-sea ecosystems becomes crucial. In this context, this study focused on the effect of high hydrostatic pressure (10.1 MPa) on turbot hepatocytes isolated from fish exposed either to chemically dispersed oil, mechanically dispersed oil or dispersant alone. Potential combined effects of oil/dispersant and hydrostatic pressure, were assessed on cell mortality (total cell death, necrosis and apoptosis), cell viability and on hepatocyte oxygen consumption (MO2). No change in cell mortality was observed in any of the experimental conditions, whereas, the results of cell viability showed a strong and significant increase in the two oil groups independently of the pressure exposure. Finally, oil exposure and hydrostatic pressure have additive effects on oxygen consumption at a cellular level. Presence of dispersant prevent any MO2 increase in our experimental conditions. These mechanistic effects leading to this increased energetic demand and its eventual inhibition by dispersant must be investigated in further experiments.

Dietary Astragalus polysaccharides ameliorates the growth performance, antioxidant capacity and immune responses in turbot (Scophthalmus maximus L.).

Supplying immunostimulants to aquatic feed has been an effective way to enhance the health of aquatic animals and substitute for antibiotics. In the present study, the potential effects of Astragalus polysaccharides (APS) were evaluated in turbot, Scophthalmus maximus. Two levels of APS (50 and 150 mg/kg) were added to the basal diet (CON) and a 63-day growth trial (initial weight 10.13 ± 0.04 g) was conducted. As the results showed, significant improvement on growth performance in the APS groups were observed. In addition, dietary 150 mg/kg APS significantly increased the total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-PX) and lysozyme activities in liver. Meanwhile, APS diets induced the mRNA expression of toll-like receptors (TLRs) such as tlr5α, tlr5ß, tlr8 and tlr21, while reduced the expression of tlr3 and tlr22. The expression of inflammatory genes myeloid differentiation factor 88 and nuclear factor kappa b p65 and pro-inflammatory cytokines tumor necrosis factor-α and interleukin-1ß were up-regulated in APS groups while the expression of anti-inflammatory cytokine transforming growth factor beta was inhibited. Taken together, the present study indicated that Astragalus polysaccharides could remarkably enhance the growth performance, antioxidant activity and maintain an active immune response in turbot.