Understanding phosphorus mobilization mechanisms in acidic soil amended with calcium-silicon-magnesium-potassium fertilizer.

Calcium-silicon-magnesium-potassium fertilizer (CSMP) is usually used as an amendment to counteract soil acidification caused by historical excessive nitrogen (N) applications. However, the impact of CSMP addition on phosphorus (P) mobilization in acidic soils and the related mechanisms are not fully understood. Specifically, a knowledge gap exists with regards to changes in soil extracellular enzymes that contribute to P release. Such a knowledge gap was investigated by an incubation study with four treatments: i) initial soil (Control), ii) urea (60 mg kg-1) addition (U); iii) CSMP (1%) addition (CSMP) and iv) urea (60 mg kg-1) and CSMP (1%) additions (U + CSMP). Phosphorus mobilization induced by different processes was distinguished by biologically based P extraction. The Langmuir equation, K edge X-ray absorption near-edge structure spectroscopy, and ecoenzyme vector analysis according to the extracellular enzyme activity stoichiometry were deployed to investigate soil P sorption intensity, precipitation species, and microbial-driven turnover of organophosphorus. Results showed that CaCl2 extractable P (or citric acid extractable P) content increased by 63.4% (or 39.2%) in the soil with CSMP addition, compared with the study control. The accelerated mobilization of aluminum (Al)/iron (Fe)-bound P after CSMP addition, indicated by the reduction of the sum of FePO4·2H2O and AlPO4 proportion, contributed to this increase. The decrease of P sorption capacity can also be responsible for it. The CSMP addition increased enzyme extractable P in the soil nearly 7-fold and mitigated the limitations of carbon (C) and P for soil microorganisms (indicated by the enzyme stoichiometry and ecoenzyme vector analysis), suggesting that microbial turnover processes also contribute to P mobilization in amended acidic soil. These findings indicate that the P mobilization in CSMP amended acidic soil not only attributed to both decreasing P sorption capacity and dissolving phosphate precipitation, but also to the increase of the microbial turnover of the organophosphorus pool.

Numerical Study on the Effect of an Improved Three-Partition Baffle Flow Field on Proton Exchange Membrane Fuel Cell Performance.

The proton exchange membrane fuel cell (PEMFC) is a type of efficient and environmentally friendly battery. The structure of its bipolar plate directly affects reactant transport and liquid water removal and thereby affects the fuel cell performance. An improved three-partition trapezoidal baffle flow field based on the conventional trapezoidal baffle flow field design is proposed in this paper. A three-dimensional multiphase PEMFC model was established by considering the Forchheimer inertial effect. The mass-transfer characteristics and fuel cell performance of the improved three-partition baffle flow field were compared with those of the conventional parallel flow field and ordinary trapezoidal baffle flow field. It was observed that both improved three-partition baffle flow field and ordinary trapezoidal baffle flow field reduced the flow velocity near the baffle to enhance the inertial effect and mass transfer. In addition, improving the three-partition baffle flow field by further optimizing the baffle heights in different regions of the ordinary trapezoidal baffle flow field improved the transverse flow transmission and the inertial effect near the three-partition baffles. The water removal capability of the porous electrode and the PEMFC performance also improved. The net power of the improved three-partition baffle flow field increased by 4.8% compared with that of the conventional parallel flow field. This study provides an effective reference for the study of the PEMFC bipolar plate structure.

A meta-analysis to examine whether nitrification inhibitors work through selectively inhibiting ammonia-oxidizing bacteria.

Nitrification inhibitor (NI) is often claimed to be efficient in mitigating nitrogen (N) losses from agricultural production systems by slowing down nitrification. Increasing evidence suggests that ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) have the genetic potential to produce nitrous oxide (N2O) and perform the first step of nitrification, but their contribution to N2O and nitrification remains unclear. Furthermore, both AOA and AOB are probably targets for NIs, but a quantitative synthesis is lacking to identify the "indicator microbe" as the best predictor of NI efficiency under different environmental conditions. In this present study, a meta-analysis to assess the response characteristics of AOB and AOA to NI application was conducted and the relationship between NI efficiency and the AOA and AOB amoA genes response under different conditions was evaluated. The dataset consisted of 48 papers (214 observations). This study showed that NIs on average reduced 58.1% of N2O emissions and increased 71.4% of soil NH 4 + concentrations, respectively. When 3, 4-dimethylpyrazole phosphate (DMPP) was applied with both organic and inorganic fertilizers in alkaline medium soils, it had higher efficacy of decreasing N2O emissions than in acidic soils. The abundance of AOB amoA genes was dramatically reduced by about 50% with NI application in most soil types. Decrease in N2O emissions with NI addition was significantly correlated with AOB changes (R 2 = 0.135, n = 110, P < 0.01) rather than changes in AOA, and there was an obvious correlation between the changes in NH 4 + concentration and AOB amoA gene abundance after NI application (R 2 = 0.037, n = 136, P = 0.014). The results indicated the principal role of AOB in nitrification, furthermore, AOB would be the best predictor of NI efficiency.

The role of the biogas slurry microbial communities in suppressing fusarium wilt of cucumber.

The clarification of the suppressive effect of biogas slurries (BSs) on soil-borne plant pathogens is needed for their large-scale use as a biocontrol tool in potting soil in order to understand the mechanisms of suppression. In this study, pig manure biogas slurry (PS) and vinasse biogas slurry (VS) were used to conduct assays of pathogen mycelial growth suppression and pot experiment to evaluate their effects on the growth of Fusarium. oxysporum f. sp. cucumerinum (FOC) mycelia and cucumber fusarium wilt. The microbial communities of the PS and VS were deeply analyzed to explore the key taxa and potential mechanisms. Results showed that the PS and VS have similar suppression on FOC mycelia and on the control efficiency, while they were significantly weakened when the PS and VS were used after sterilization. The microbial parameters of the two BSs were obviously different, and functional microbial taxa for disease resistance were observed in the two BSs. Spearman correlation showed that genera of the Pseudomonas, Ochrobactrum, Papiliotrema, etc., were the suppression-related taxa in the PS, while Leucobacter, unclassified_Microbacteriaceae, etc. in the VS. Overall, various key taxa in the PS and VS produced similar suppression on cucumber fusarium wilt.

Topology Optimization and Multiobjective Optimization for Drive Axle Housing of a Rear Axle Drive Truck.

As one of the important load-bearing components of a truck, the drive axle housing must meet the requirements of stiffness and strength. The traditional design method uses redundancy design to meet the performance requirements. The joint design between the three-dimensional mathematical model and finite element model is adopted, and the optimal design of the drive axle housing is realized based on topology optimization and multiobjective optimization. Firstly, the static analysis of the drive axle housing of a rear axle drive truck was carried out with four typical working conditions. It was concluded that the four working conditions all operate under the yield limit of the material, and it was found that the maximum equivalent stress of the four working conditions occurs at the step of the half-shaft casing. Among the four working conditions, the most critical one is the maximum vertical force working condition. Then, based on the maximum vertical force working condition, the fatigue life analysis is conducted, and the minimum fatigue life appears at the transition position of the half-shaft sleeve and the arc transition position of the main reducer chamber. The remaining parts can meet the design requirements. The overall safety factor of the drive axle housing is mainly between 1 and 5 when operating under this working condition. Then, through modal analysis, the first to sixth natural frequency and vibration modes of the drive axle housing are extracted. Based on the modal analysis, the dynamic characteristics of the drive axle housing are further studied by harmonic response analysis and random vibration analysis. Finally, two kinds of lightweight optimization schemes for the drive axle housing are given. Topology optimization reduces the mass of the drive axle housing by 17.4%, but the overall performance slightly decreases. Then, the five dimensional parameters of the drive axle housing are selected as design variables. The mass, maximum deformation, equivalent stress, service life, and the first-, second- and third-order natural frequencies are defined as objective functions. Through the optimal space-filling design method, the experimental designs are performed and the sample points are obtained. Based on the results of experiment design, the multiobjective genetic algorithm and response surface method are combined to optimize the objective functions. The analysis results show that the mass is reduced by 4.35%, the equivalent stress is reduced by 21.05%, the minimum life is increased by 72.28%, and the first-, second-, and third-order natural frequency are also increased to varying degrees. Two different optimization strategies are provided for the design of the drive axle housing.

Experimental and simulation study on heat transfer characteristics of aluminium alloy piston under transition conditions.

In order to explore the thermal load change of the diesel engine piston under transitional conditions, and the influence of the position of cooling gallery on the heat transfer characteristics of the piston. An off-road high-pressure common-rail diesel engine is chosen as the research object. The sequence coupling method is used to establish the fluid-solid coupling heat transfer simulation model of the piston-gallery under the transition conditions of cold start, urgent acceleration and rapid deceleration. The Pareto optimization algorithm is introduced to optimize the position of the cooling gallery to reduce the maximum temperature and maximum thermal stress of the piston. The results show that the maximum temperature of the piston can be reduced by reducing the distance between the cooling gallery and the throat area under the maximum torque condition, and that the maximum thermal stress of the piston can be reduced by reducing the distance between the cooling gallery and the throat area or by increasing the distance between the cooling gallery and the ring area. Compared with the original design, the maximum temperature of Design A decreases by 1.28 °C while the maximum thermal stress decreases by 2.07 MPa. The maximum temperature and maximum thermal stress of Design B decreases by 0.22 °C and 0.5 MPa, respectively. The maximum thermal stress of Design C decreases by 2.67 MPa when the maximum temperature increases by 1.15 °C. The maximum change in temperature of the three typical designs and the original design of the piston throat under cold start, urgent acceleration and rapid deceleration conditions reached 207.29 °C, 136.78 °C and 9.89 °C, and the maximum change of thermal stress reached 8.62 MPa, 20.43 MPa, 4.08 MPa, respectively. The maximum change in temperature of the piston first ring groove under cold start, urgent acceleration and rapid deceleration conditions reached 172.00 °C, 83.52 °C and 7.36 °C, and the maximum change in thermal stress reached 22.96 MPa, 43.10 MPa, 5.72 MPa, respectively. The conclusions obtained can provide boundary conditions for further study of the thermal load change law of the same type of pistons, and also provide a theoretical basis for diesel engine piston structure optimization and the performance improvement.

Experimental and simulation study on aluminium alloy piston based on thermal barrier coating.

Thermal barrier coatings (TBCs) have low thermal conductivity, effectively reducing the temperature of the metal matrix and improving thermal performance, knock resistance, and combustion performance of the piston. In this study, an off-road high-pressure common-rail diesel engine was chosen as the research object. Combined with the test results of the piston temperature field under the rated power and maximum torque conditions, a finite element simulation model of the thermal barrier coating piston was established. This model enabled the distribution characteristics and variation laws of the temperature field, stress, and deformation of the thermal barrier coating on the piston matrix to be analysed. The results show that the maximum temperature of the TBC piston is 12.2% and 13.73% lower than that of the aluminium alloy piston under the rated power and maximum torque conditions, respectively. The thermal stresses of the TBC piston at the top of the cavity were 25.9% and 26.8% lower than those of the aluminium piston, while the thermo-mechanical coupling stress of the TBC piston was slightly higher than that of the aluminium piston-1.2 MPa and 3.7 MPa in the bottom of the combustion chamber with geometric mutation, respectively. The radial thermal deformation of the TBC piston was 0.067 mm and 0.073 mm lower than that of the aluminium piston, with the radial thermo-mechanical coupling deformation also decreasing by 0.069 mm and 0.075 mm, respectively. The radial thermal deformation of the piston in the direction parallel to the pinhole axis was greater than that in the direction perpendicular to the pinhole axis; the difference in the magnitude of the change results in uneven thermal deformation of the piston.

Research on the influence of key structural parameters on piston secondary motion.

Piston secondary motion not only influences the side knocking of piston and frictional loss, but also influence the in-cylinder oil consumption and gas blow-by. An inline four-cylinder common rail diesel engine was chosen as the research object. Dynamic simulation model of piston assembly was built based on the piston and cylinder liner temperature field test. The impacts of pinhole offset, liner clearance and piston skirt ovality on piston secondary motion were researched. Based on the surface response method, the influence of multiple factors on friction power loss and slapping energy is estimated. The results indicate that: in-cylinder stress condition of piston will change with its structural parameters, then the secondary motion of piston will be affected as a result. Pinhole offset, liner clearance, piston skirt ovality and the interaction of the latter two all have significant effects on the friction power loss, while the slapping energy is significantly affected by liner clearance. Therefore, the parameters can be designed based on the significance level to optimize the secondary motion characteristics of the piston.

Environmental persistent free radicals in diesel engine exhaust particles at different altitudes and engine speeds.

The occurrence of environmental persistent free radicals (EPFRs) in the environment has attracted a great deal of research attention. Although the major sources of EPFRs in the environment is diesel engine exhaust, the study on the emission characteristics of EPFRs at different working conditions is still very limited. An integrated engine system was adopted to simulate different working conditions of various altitudes and engine speeds, and to examine the emission process of a diesel engine. The results suggested that low engine speed and high altitude are generally associated with high PM10 emission with more stable and ordered structures. Based on the analysis of PAHs on solid and gas phases, PM10 generated from diesel engine at altitude higher than 2000 m may contain substantial amounts of PAHs embedded inside particles, but not adsorbed on the surface. EPFRs signal up to 1.66 × 1020 spins/g were detected in PM10 of the diesel exhaust. Higher engine speed and lower altitude were associated with stronger EPR signals on PM10. However, the accumulated EPR signal intensities after consuming 1 L of diesel were higher at lower engine speed and higher altitude, suggesting higher overall risks. A positive correlation between R value (signal strength ratio of D and G peaks on the Raman spectra) and EPFRs intensity indicated that the EPR signals were associated with the defects of carbon structure. EPFRs intensity in particles showed no significant change in dark, and over 70% of the EPR signals survived under UV light in a one-month aging simulation. The strong persistence of these EPFRs suggested their potential long lasting and widespread risks, which should be investigated extensively.

Complete genome sequence of Exiguobacterium mexicanum A-EM, isolated from seafloor hydrothermal vents in Atlantic Ocean.

Exiguobacterium mexicanum A-EM was isolated from seafloor hydrothermal vents(Caifan field, 14.0S 14.4 W) and was shown to degrade toxins and contaminants. Here, we present the complete genome sequence of A-EM, consisting of 2,412,492 bp, with a GC content of 53.16%. A-EM sequence contains genes encoding enzymes that degrade toxins and contaminants. Complete genome sequence of the strain A-EM can further provide insights into microbial adaption to the seafloor hydrothermal system and the genomic basis for the biotechnological application of strain A-EM as an efficient agent to degrade environmental contaminants.

Molecular function of gonadotrophins and their receptors in the ovarian development of turbot (Scophthalmus maximus).

Gonadotropins (GtHs) and their receptors (follicle-stimulating hormone receptor, FSHR; luteinizing hormone receptor, LHR) are involved in the regulation of gametogenesis and play important roles during the reproductive cycles in vertebrate species, including fish. This minireview focuses on the molecular characterization and quantification of GtHs (common glycoprotein α subunit CGα, FSHß, and LHß) and their receptors (FSHR and LHR) throughout the reproductive cycle of female turbot Scophthalmus maximus. Information about GtHs, FSHR, LHR as well as other ligand-receptors interaction from different teleosts are also included in this review for the implications they may have on the functions of GtHs, FSHR and LHR in the reproductive development of turbot. These findings may enhance our understanding of the physiological roles of the GtHs, FSHR and LHR in controlling of flatfish ovarian development during the reproductive cycle and contributing to the improvement of management strategies for turbots in captivity.

Expression and localization study of pIgR in the late stage of embryo development in turbot (Scophthalmus maximus).

The receptor responsible for maternofetal transmission of immunoglobulin (Igs) in the teleosts is not clear. Polymeric immunoglobulin receptor (pIgR) specifically binds with IgA and IgM and mediates the transcytosis of intracellular polymeric immunoglobulins (pIgs) at the mucosal surface to protect against pathogens. Hence there is a possibility that it may be involved in the transmission of maternal Igs. The aim of the present study was to detect the expression and localization of pIgR during embryonal development in turbot (Scophthalmus maximus). pIgR gene was first cloned from eggs and embryos of turbot with or without parent immunization. The expression and distribution of pIgR in unfertilized egg and in embryos ranging from day 1 to day 5 after fertilization were analyzed using reverse transcriptase quantitative polymerase chain reaction and in situ hybridization. pIgR gene was detected in all eggs and embryos at different stages of development, with the highest level detected on the 5th day. pIgR mRNA was observed to be first located in the whole blastoderm and enveloped the yolk sac. Later, it was located around entoderm including primary digestive tract and pronephric tubule tract, and finally it was located at the joint of abdomen and vitelline membrane. Then, Eukaryotic expression plasmid carrying pIgR gene was constructed and transfected into HEK293T cells. Results showed mature pIgR protein located on the cellular membrane, and could bound IgM in vitro. Our findings provide information for studying the involvement of pIgR in maternal Igs transportation in turbot.

Effect of a Sodium Alginate Coating Infused with Tea Polyphenols on the Quality of Fresh Japanese Sea Bass (Lateolabrax japonicas) Fillets.

Sodium alginate (SA) and tea polyphenols (TP) are natural preservatives commonly used in the food industry, including the production of fish products. The effect of SA coating infused with TP on the quality of fresh Japanese sea bass (Lateolabrax japonicas) fillets was evaluated over a 20-day period at 4 °C. SA (1.5%, w/v) or TP (0.5%, w/v) treatment alone, and the SA coating infused with TP (SA-TP) all reduced microbial counts, with the SA-TP providing the greatest effect. Fish fillet samples treated with SA-TP had significantly lower levels of total volatile basic nitrogen, lipid oxidation, and protein decomposition during the storage period, relative to the remaining treatments. The samples treated with SA-TP had the highest sensory quality rating as well. Collectively, sodium alginate coating infused with tea polyphenols may represent a promising treatment for preservation of Japanese sea bass fillets during cold storage. PRACTICAL APPLICATION: The sodium alginate-tea polyphenols composite coating has strong potential to be used as a new biopreservative for maintaining fish fillet quality.

Effect of crowding stress on the immune response in turbot (Scophthalmus maximus) vaccinated with attenuated Edwardsiella tarda.

The aim of this study was to evaluate the immune responses in turbot, Scophthalmus maximus, treated with 1 × 107 cfu/ml attenuated Edwardsiella tarda (0.1 ml/fish) under low density (LD; ∼5.25-5.13 kg/m2, initial to final density), medium density (MD; ∼10.41-13.95 kg/m2), and high density (HD; ∼20.53-30.77 kg/m2) conditions for 8 weeks. The results showed that there was a peak value in the percentage of sIg+ (surface immunoglobulin-positive) cells in blood leucocytes (BL), spleen leucocytes (SL), and pronephros leucocytes (PL) during the sixth week in the HD, which was delayed by week compared with the other groups. The specific immunoglobulin M (IgM) antibody levels increased from the first week in all groups and reached a peak in the fifth week in the LD and MD groups, but in the sixth week in the HD group. The serum cortisol levels were greater in the HD group compared with the other groups in the last 3 or 4 weeks. These results show that stocking turbot at a LD obtained the most effective immunization, and thus we conclude that crowding stress may reduce the ability to deal with immune challenge.

Developmental changes in digestive enzyme activity in American shad, Alosa sapidissima, during early ontogeny.

In order to assess the digestive physiological capacity of the American shad Alosa sapidissima and to establish feeding protocols that match larval nutritional requirements, we investigated the ontogenesis of digestive enzymes (trypsin, amylase, lipase, pepsin, alkaline phosphatase, and leucine aminopeptidase) in larvae, from hatching to 45 days after hatching (DAH). We found that all of the target enzymes were present at hatching, except pepsin, which indicated an initial ability to digest nutrients and precocious digestive system development. Trypsin rapidly increased to a maximum at 14 DAH. Amylase sharply increased until 10 DAH and exhibited a second increase at 33 DAH, which coincided with the introduction of microdiet at 30 DAH, thereby suggesting that the increase was associated with the microdiet carbohydrate content. Lipase increased until 14 DAH, decreased until 27 DAH, and then increased until 45 DAH. Pepsin was first detected at 27 DAH and then sharply increased until 45 DAH, which suggested the formation of a functional stomach. Both alkaline phosphatase and leucine aminopeptidase markedly increased until 18 DAH, which indicated intestinal maturation. According to our results, we conclude that American shad larvae possess the functional digestive system before mouth opening, and the significant increases in lipase, amylase, pepsin, and intestinal enzyme activities between 27 and 33 DAH suggest that larvae can be successfully weaned onto microdiets around this age.

Effects of stocking density on antioxidant status, metabolism and immune response in juvenile turbot (Scophthalmus maximus).

This study was designed to evaluate the physiological and immune responses of juvenile turbot to stocking density. Turbot (average weight 185.4g) were reared for 120days in a land based recirculating aquaculture system (RAS) under three stocking densities: low density (LD, ~9.3-26.1kg/m2, initial to final density), medium density (MD, ~13.6-38.2kg/m2) and high density (HD, ~19.1-52.3kg/m2). Fish were sampled at days 0, 40, 80 and 120 to obtain growth parameters and liver tissues. No significant difference was detected in growth, biochemical parameters and gene expression among the three densities until at the final sampling (day 120). At the end of this trial, fish reared in HD group showed lower specific growth rate (SGR) and mean weight than those reared in LD and MD groups. Similarly, oxidative stress and metabolism analyses represented that antioxidants (superoxide dismutase (SOD), catalase (CAT), glutathione (GSH)) and metabolic enzymes (glycerol-3-phosphate dehydrogenase (G3PDH) and glucose-6-phosphate dehydrogenase (G6PDH)) clearly reduced in the liver of turbot reared in HD group. The gene expression data showed that glutathione S-transferase (GST), cytochrome P450 1A (CYP1A), heat shock protein 70 (HSP 70) and metallothionein (MT) mRNA levels were significantly up-regulated, and lysozyme (LYS) and hepcidin (HAMP) mRNA levels were significantly down-regulated in HD group on day 120. Overall, our results indicate that overly high stocking density might block the activities of metabolic and antioxidant enzymes, and cause physiological stress and immunosuppression in turbot.

Molecular characterization and expression analysis of AMPK α subunit isoform genes from Scophthalmus maximus responding to salinity stress.

AMP-activated protein kinase (AMPK) is a highly conserved and multi-functional protein kinase that plays important roles in both intracellular energy balance and cellular stress response. In the present study, molecular characterization, tissue distribution and gene expression levels of the AMPK α1 and α2 genes from turbot (Scophthalmus maximus) under salinity stress are described. The complete coding regions of the AMPK α1 and α2 genes were isolated from turbot through degenerate primers in combination with RACE using muscle cDNA. The complete coding regions of AMPK α1 (1722 bp) and α2 (1674 bp) encoded 573 and 557 amino acids peptides, respectively. Multiple alignments, structural analysis and phylogenetic tree construction indicated that S. maximus AMPK α1 and α2 shared a high amino acid identity with other species, especially fish. AMPK α1 and α2 genes could be detected in all tested tissues, indicating that they are constitutively expressed. Salinity challenges significantly altered the gene expression levels of AMPK α1 and α2 mRNA in a salinity- and time-dependent manners in S. maximus gill tissues, suggesting that AMPK α1 and α2 played important roles in mediating the salinity stress in S. maximus. The expression levels of AMPK α1 and α2 mRNA were a positive correlation with gill Na+, K+-ATPase activities. These findings will aid our understanding of the molecular mechanism of juvenile turbot in response to environmental salinity changes.

Expression of insulin-like growth factors at mRNA levels during the metamorphic development of turbot (Scophthalmus maximus).

Insulin-like growth factors I and II (IGF-I and IGF-II) are important regulators of vertebrate growth and development. This study characterized the mRNA expressions of igf-i and igf-ii during turbot (Scophthalmus maximus) metamorphosis to elucidate the possible regulatory role of the IGF system in flatfish metamorphosis. Results showed that the mRNA levels of igf-i significantly increased at the early-metamorphosis stage and then gradually decreased until metamorphosis was completed. By contrast, mRNA levels of igf-ii significantly increased at the pre-metamorphosis stage and then substantially decreased during metamorphosis. Meanwhile, the whole-body thyroxine (T4) levels varied during larval metamorphosis, and the highest value was observed in the climax-metamorphosis. The mRNA levels of igf-i significantly increased and decreased by T4 and thiourea (TU, inhibitor of endogenous thyroid hormone) during metamorphosis, respectively. Conversely, the mRNA levels of igf-ii remained unchanged. Furthermore, TU significantly inhibited the T4-induced mRNA up-regulation of igf-i during metamorphosis. The whole-body thyroxine (T4) levels were significantly increased and decreased by T4 and TU during metamorphosis, respectively. These results suggested that igf-i and igf-ii may play different functional roles in larval development stages, and igf-i may have a crucial function in regulating the early metamorphic development of turbot. These findings may enhance our understanding of the potential roles of the IGF system to control flatfish metamorphosis and contribute to the improvement of broodstock management for larvae.

Stress and immune responses in skin of turbot (Scophthalmus maximus) under different stocking densities.

Fish skin and its mucus provide the first line of defense against chemical, physical and biological stressors, but little is known about the role of skin and its mucus in immune response to crowding stress. In the present study, we investigated the stress and immune responses in skin of turbot (Scophthalmus maximus) under different stocking densities. Turbot (average weight 185.4 g) were reared for 120 days under three densities: low density (LD), medium density (MD), and high density (HD). After 120 days, fish were weighed and sampled to obtain blood, mucus and skin tissues which were used for analyses of biochemical parameters and genes expression. The results showed HD treatment significantly suppressed growth and enhanced plasma cortisol and glucose levels (P < 0.05). In mucus, the activities of lysozyme (LZM), alkaline phosphatase (ALP) and esterase in HD treatment were lower than LD and MD treatments (P < 0.05) In skin, HD treatment resulted in up-regulation in malondialdehyde (MDA) formation and heat shock protein 70 (HSP 70) mRNA level, and down-regulation in activity of superoxide dismutase (SOD) and the transcriptions of glutathione-s-transferase (GST), interleukin-1ß (IL-1ß), tumor necrosis factor -α (TNF-α), insulin-like growth factor- (IGF-) and LZM (P < 0.05). Overall, the data suggested that overly high stocking density was a stressor which caused an immunosuppression in skin of turbot. Moreover, this information would help to understand the skin immunity and their relation with stress and disease in fish.

The physiological performance and immune response of juvenile turbot (Scophthalmus maximus) to nitrite exposure.

Nitrite (NO(2-)) is the most common toxic nitrogenous compound in aquatic environment. The aim of the present study was to investigate the effects of nitrite physiological performance and immune response of turbot. Fish were exposed to 0, 0.02, 0.08, 0.4 and 0.8 mM nitrite for 96 h. After 0, 24, 48 and 96 h of exposure, blood were collected to measure the levels of glutamate pyruvate transaminase (GPT), glutamate oxalate transaminase (GOT), alkaline phosphatase (ALP), total protein (TP), albumin (Alb), complement C3 (C3), complement C4 (C4), immunoglobulin M (IgM) and lysozyme (LYS); gill samples were taken to analyze mRNA levels of LYS, heat shock protein 70 (HSP 70), heat shock protein 90 (HSP 90), metallothionein (MT), toll-like receptor 3 (TLR-3), tumor necrosis factor α (TNF-α), interleukin-1ß (IL-1ß) and insulin-like growth factor I (IGF-I). The results showed that nitrite (0.4 and/or 0.8mM) significantly increased the levels of GPT, GOT, ALP, C3 and C4, reduced the levels of IgM and LYS, up-regulated the gene expressions of HSP 70, HSP 90, MT, TLR-3, TNF-α and IL-1ß, and down-regulated the gene expressions of LYS and IGF-1 after 48 and 96 h of exposure. Based on the results, it can be concluded that high level nitrite exposure results in dysfunction of the blood physiology and immunity in turbot. Further, this study will be helpful to understand the mechanism of aquatic toxicology induced by nitrite in marine fish.