Review on the immunology of European sea bass Dicentrarchus labrax

Current Status of Probiotics in European Sea Bass Aquaculture as One Important Mediterranean and Atlantic Commercial Species: A Review

European sea bass production has increased in recent decades. This increase is associated with an annually rising demand for sea bass, which encourages the aquaculture industries to increase their production to meet that demand. However, this intensification has repercussions on the animals, causing stress that is usually accompanied by dysbiosis, low feed-conversion rates, and immunodepression, among other factors. Therefore, the appearance of pathogenic diseases is common in these industries after immunodepression. Seeking to enhance animal welfare, researchers have focused on alternative approaches such as probiotic application. The use of probiotics in European sea bass production is presented as an ecological, safe, and viable alternative in addition to enhancing different host parameters such as growth performance, feed utilization, immunity, disease resistance, and fish survival against different pathogens through inclusion in fish diets through vectors and/or in water columns. Accordingly, the aim of this review is to present recent research findings on the application of probiotics in European sea bass aquaculture and their effect on growth performance, microbial diversity, enzyme production, immunity, disease resistance, and survival in order to help future research.

Characterization of digenetic trematodes infecting African catfish (Clarias gariepinus) based on integrated morphological, molecular, histopathological, and immunological examination

Parasitic infection may cause massive losses in Clarias gariepinus fries and fingerlings. Therefore, this study aimed to characterize the digenetic trematodes species (two adults' flukes and one metacercariae) infecting African catfish Clarias gariepinus, as well as their histopathological impacts on infected fish. The intestinal flukes were identified as Orientocreadium batrachoides and Masenia bangweulensis based on their morphological and molecular characteristics. Sequencing of their 28S (LSU rRNA) and 18S rRNA (SSU rRNA) genes confirmed that these trematodes belong to the families Orientocreadiidae and Cephalogonimidae, respectively. The metacercariae trematode infecting skin and muscles were only morphologically identified as Cyanodiplostomum sp. The gene expression levels of MHC II increased in naturally infected fish either with O. batrachoides or Cyanodiplostomum sp. alone, compared with uninfected catfish. In addition, lysozyme levels in individual fish serum increased in catfish infected either with O. batrachoides or Cyanodiplostomum sp. alone. Histopathological examination of the skin revealed embedded parasitic cysts that displaced tissue in the dermis. Surrounding tissues were infiltrated with melanomacrophages and displayed dermal edema. Histopathological analysis showed O. batrachoides or M. bangweulensis between the gastric folds of the stomach of infected catfish, causing infiltration of mononuclear inflammatory cells in the lamina propria.

Dietary garlic and chitosan enhanced the antioxidant capacity, immunity, and modulated the transcription of HSP70 and Cytokine genes in Zearalenone-intoxicated European seabass

The present study was performed to evaluate the toxic effects of feed-born zearalenone (ZEN) on antioxidative status, immunity, transcriptomic responses of European seabass, and the modulating roles of dietary garlic and/or chitosan powders. Fish (30.7 ± 0.6 g) were randomly arranged in five experimental groups (in triplicates), whereas the first group was fed on the control diet only without any supplements (control), and the second group was fed on the basal diet contaminated with ZEN (0.725 mg/kg diet). Three other groups were fed on ZEN-contaminated diets and simultaneously supplemented with garlic powder (GP) (30 g/kg diet) (ZEN + GP), chitosan powder (CH) (10 g/kg diet) (ZEN + CH), and a mixture of GP and CH (ZEN + GP + CH). Fish were fed on the experimental diets thrice a day for 4 weeks. Two-way ANOVA revealed a gradual decline in serum superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities in the ZEN group reaching their lowest levels at the 4th week. Contrariwise, malondialdehyde levels were markedly higher in the ZEN group reaching their highest values at the end of the experiment. A significant decline of total immunoglobulins (P < 0.05) was observed in the serum of the ZEN group, especially after the 4th week. Moreover, significant down-regulation of interleukin-4 (IL-4) and interleukin 1 beta (IL-1β) genes (P < 0.05) alongside significant up-regulation of tumor necrosis factor-alpha (TNF-α) and heat shock protein 70 (HSP70) genes (P < 0.05) in the liver and anterior kidney of ZEN-intoxicated group. Interestingly, dietary supplementation with GP and CH significantly attenuated ZEN-induced oxidative stress, immunosuppression, and modulated transcriptomic responses of ZEN-exposed fish. Moreover, combined dietary supplementation of both feed additives resulted in better effects than each one alone.

Survival and gene expression responses in immune challenged larval lake sturgeon

Larval lake sturgeon, Acipenser fulvescens, reared in hatcheries for stock enhancement of wild populations may be susceptible to early opportunistic bacterial infection. Thus, we examined survival and whole-body mRNA expression of both stress- and immune-related genes (MyD88, IL-1β, StAR, GR1, and HSP70) in 30 days post fertilization larval lake sturgeon following immune challenge with lipopolysaccharides (LPS). Larval sturgeon were exposed to 0, 25, 50, 100, 150, and 200 μg ml^-1 LPS and sampled after 30 min, 4 h, and 48 h. Mortality was zero in 0 and 25 μg ml^-1 LPS; 37.5% in 50 μg ml^-1 LPS and 100% in the higher concentrations. Expression of MyD88 and StAR mRNA were positively correlated and increased with time in the 50 μg ml^-1 LPS treatment. There was an influence of both treatment and time on IL-1β mRNA, with expression 10-fold higher than controls after 4 h. Expression of HSP70 mRNA was suppressed within 30 min of 50 μg ml^-1 LPS exposure and remained so throughout the time course. Correlated mRNA expression of GR1 with MyD88, StAR and IL-1β suggests a potential relationship between the innate immune and glucocorticoid responses of larval lake sturgeon during this early developmental stage. Data presented suggest that larval lake sturgeon largely responded with predicted changes in gene expression of immune related and stress response genes following LPS challenge. This study provides a foundation for future research examining the effects of hatchery and naturally occurring stressors on the immune responses of larval lake sturgeon.

Black soldier fly (Hermetia illucens) larvae meal in diets of European seabass: Effects on antioxidative capacity, non-specific immunity, transcriptomic responses, and resistance to the challenge with Vibrio alginolyticus

Black soldier fly larvae meal (BSFLM) has been successfully demonstrated as a promising fish meal (FM) replacer in diets of several fish species including European seabass (Dicentrarchus labrax). However, its impacts on antioxidant capacity, and immune responses of treated fish are still poorly understood. A 60-day feeding trial was carried out to evaluate the effects of partial substitution of FM with different levels of dry BSFLM on the antioxidative status, non-specific immunity, transcriptomic responses, and resistance of European seabass to the challenge with Vibrio alginolyticus. Four isoproteic (45%) and isolipidic diets were formulated by replacing 0.0%, 25%, 35%, and 50% of the dietary FM. Each diet was randomly assigned to four fish groups (in triplicates) (initial mean body weight, 12.1 ± 0.21 g) (20 fish per aquarium) (n = 240). Fish were fed three times daily to the apparent satiation. At the end of the feeding trial, serum antioxidant biomarkers such as malondialdehyde levels, and catalase, superoxide dismutase, and glutathione peroxidase enzyme activities were significantly increased in all BSFLM groups in a dose-dependent manner compared to the control group (P < 0.05). The non-specific immune indices, including phagocytic activity, phagocytic index, serum lysozyme and respiratory burst activities were significantly elevated in BSFLM groups compared to those in the control group (P < 0.05). Significant upregulation of the mRNA expression levels of hepatic heat shock protein 70, interleukin-1beta and interleukin-10 genes were observed in all BSFLM groups compared to the control group (P < 0.05). Additionally, after the challenge with V. alginolyticus, the relative percent of survival was significantly elevated in fish groups fed on diets containing graded levels of BSFLM over the control group (P < 0.05). Conclusively, the present study suggests the potential efficacy of partial replacement of dietary FM protein for up to 50% by BSFLM without negative effects on fish health with possible potentiation of the antioxidative status, and the immune responses of the European seabass.

Effects of extreme ambient temperature in European seabass, Dicentrarchus labrax acclimated at different salinities: Growth performance, metabolic and molecular stress responses

Extreme weather events are becoming more intense and frequent as a result of climate change. The modulation of hemato-physiological potential as a compensatory response to extreme warm events combined with different salinities is poorly understood. This study aimed to assess the hemato-physiological and molecular response of European seabass, Dicentrarchus labrax exposed to extreme warm temperature (33 °C) after prior acclimatization at 32 psu, 12 psu, 6 psu, and 2 psu water. Fish were acclimated to 32 psu, 12 psu, 6 psu, and 2 psu followed by 10 days extreme warm (33 °C) exposure. Along with growth performance and survival, hemato-physiological response and molecular response of fish were recorded. Fish held at 32 psu and 2 psu exhibited significantly lower growth performance and survival than those at 12 psu and 6 psu (p < 0.05). Red blood cells (RBC), hematocrit, and hemoglobin content were significantly decreased, while white blood cells (WBC), erythrocytic cellular abnormalities (ECA) and erythrocytic nuclear abnormalities (ENA) were found to increase significantly in 32 psu and 2 psu fish (p < 0.05). Plasma lactate was found to increase significantly in 32 psu fish on day 10 (p < 0.05). Activities of glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT), and TNF-α expression increased significantly in 32 psu and 2 psu fish (p < 0.05). Most of the repeated measured parameters indicated limited acclimation capacity during the extreme warm exposure at all four salinity groups. However, overall results indicate that European seabass acclimatized at 12 psu and 6 psu salinities, can cope better during extreme warm exposure (33 °C).

Identification and Regulation of Interleukin-17 (IL-17) Family Ligands in the Teleost Fish European Sea Bass

Interleukin-17 (IL-17) cytokine comprises a family of six ligands in mammals with proinflammatory functions, having an important role in autoimmune disorders and against bacterial, viral, and fungal pathogens. While IL-17A and IL-17F ligands are mainly produced by Th cells (Th17 cells), the rest of the ligands are expressed by other immune and non-immune cells and have different functions. The identification of IL-17 ligands in fish has revealed the presence of six members, counterparts to mammalian ones, and a teleost-specific form, the fish IL-17N. However, tissue distribution, the regulation of gene expression, and scarce bioactivity assays point to similar functions compared to mammalian ones, though this yet to be investigated and confirmed. Thus, we have identified seven IL-17 ligands in the teleost European sea bass (Dicentrarchus labrax), for the first time, corresponding to IL-17A/F1, IL-17A/F2, IL-17A/F3, IL-17C1, IL-17C2, IL-17D, and IL-17N, according to the predicted protein sequences and phylogenetic analysis. They are constitutively and widely transcribed in sea bass tissues, with some of them being mainly expressed in the thymus, brain or intestine. Upon in vitro stimulation of head-kidney leucocytes, the mRNA levels of all sea bass IL-17 ligands were up-regulated by phytohemagglutinin treatment, a well-known T cell mitogen, suggesting a major expression in T lymphocytes. By contrast, the infection of sea bass juveniles with nodavirus (NNV), a very pathogenic virus for this fish species, resulted in the up-regulation of the transcription of IL-17C1 in the head-kidney and of IL-17C1 and IL-17D in the brain, the target tissue for NNV replication. By contrast, NNV infection led to a down-regulated transcription of IL-17A/F1, IL-17A/F2, IL-17C1, IL-17C2, and IL-17D in the head-kidney and of IL-17A/F1 and IL-17A/F3 in the brain. The data are discussed accordingly with the IL-17 ligand expression and the immune response under the different situations tested.

Immuno-related gene transcription and antibody response in nodavirus (RGNNV and SJNNV)-infected European sea bass (Dicentrarchus labrax L.)

The immune response of European sea bass to RGNNV and SJNNV infections has been evaluated by quantifying the transcription of some genes involved in the IFN I system, as well as in the inflammatory and adaptive immune mechanisms. The transcription of IFN-I, ISG-12, ISG-15 and MxA genes has been analyzed in brain and head kidney, showing that RGNNV genotype induces a more intense response of the IFN I system than SJNNV in both organs. In addition, the results obtained indicate the importance of the inflammatory response in nodavirus pathogenesis, with the transcription of IL-8 and TNF-α significantly higher in brain than in head kidney, being RGNNV the strongest inductor. An important difference between the immune response induced by both genotypes refers to the IgM titre in sera, which was higher in SJNNV-inoculated fish. The acquired response is also important locally, since TR-γ transcription is higher in brain than in head kidney (especially in the RGNNV-inoculated group). To our knowledge, this is the first study addressing the sea bass anti-SJNNV immune response.

Preliminary study on expression of antimicrobial peptides in European sea bass (Dicentrarchus labrax) following in vivo infection with Vibrio anguillarum. A time course experiment

Antimicrobial polypeptides (AMPPs) are humoral components of the vertebrates and invertebrates innate immune system. Their potent broad spectrum antimicrobial activities have drawn the attention of the scientific community to their potential use not only as an alternative to antibiotics but also as functional targets for immunostimulants in order to enhance the host immunity. Fish synthesize a great number of these peptides but in European sea bass, an important fish species in the Mediterranean aquaculture, only a few AMPPs have been studied and these surveys have highlighted their functional role as predictive markers of stressful conditions. Many aspects concerning AMPP mode of action in the host during bacterial infections are still unknown. In this work a 72 h time course experiment, performed on juvenile sea bass intraperitoneally (i.p.) injected with a sub-lethal dose of Vibrio anguillarum, was aimed to investigate the mRNA expression of four specific AMPP genes and interleukin-1β (IL-1β) in skin, gills, spleen, and head kidney. AMPP genes were: dicentracin (DIC), histone-like protein 1 (HLP-1), histone-like protein 2 (HLP-2) and hemoglobin-like protein (Hb-LP). The delta-delta C(T) method in real-time RT-PCR allowed to gain more knowledge about temporal dynamics, preferential sites of expression as well as immunological and physiological role of these molecular markers. DIC was significantly up-regulated mainly in head kidney at 1.5-3 h post-infection (p.i.). HLP-1 showed an extended-time overexpression in gills and a significant up-regulation in spleen. HLP-2 was interestingly overexpressed in gills at 24 h p.i., while Hb-LP showed a significant up-regulation in skin for all the 72 h trial as well as lower but always significant values either in gills or in spleen. Different was the response of IL-1β that showed a dramatic up-regulation in spleen and head kidney at 8 h p.i. whilst in gills it displayed a severe inhibition. During this survey the i.p. stimulus surely conditioned the AMPP expression in skin and gills, especially as regards the DIC that as piscidin-related gene has an important defensive role in the mucosal tissues. However, two unconventional AMPP genes such as HLP-2 and Hb-LP, strictly related to the physiological mechanisms of fish, were less affected in terms of expression by the route of infection, being more evident in peripheral loci. These findings might suggest them as potential markers to be analyzed within plans of health survey in fish farms.

Dietary tryptophan and methionine as modulators of European seabass (Dicentrarchus labrax) immune status and inflammatory response

Amino acids regulate key metabolic pathways important to immune responses and their nutritional supply may increase synthesis of immune-related proteins. The present study aimed to evaluate the effects of dietary supplementation of tryptophan and methionine on European seabass (Dicentrarchus labrax) cellular and humoral status. The immunomodulatory effects of tryptophan and methionine during an inflammatory insult was also evaluated after intraperitoneal injection with inactivated Photobacterium damselae subsp. piscicida (Phdp). A practical isonitrogenous (45% crude protein) and isolipidic (16% crude fat) diets was formulated to include fish meal and a blend of plant feedstuffs as protein sources and fish oil as the main lipid source (CRL diet). Two other diets were formulated similar to the control but including L-tryptophan or L-methionine at ×2 the requirement level (diets TRP and MET, respectively). European seabass weighing 275 g were fed the experimental diets for a period of 15 days before being sampled (trial 1). Then, fish were subjected to a peritoneal inflammation by intraperitoneally injecting UV killed Phdp (10(6) colony forming units ml(-1)) and sampled following 4 and 24 h post-injection (trial 2). Fish injected with a saline solution served as control. The haematological profile, peripheral cell dynamics and several plasma immune parameters were determined in trials 1 and 2, whereas cell migration to the inflammatory focus was also determined in trial 2. MET positively affected European seabass immune status by improving the peripheral leucocyte response, complement activity and bactericidal capacity, a stronger cellular recruitment to the inflammatory focus, and higher plasma peroxidase and bactericidal activities. TRP also seemed to improve immunostimulation, as there was a trend to augment both cell-mediated immunity and humoral capacity. However, TRP failed to improve an inflammatory response, verified by a decrease in blood phagocyte numbers and lack of immune cells recruitment. In summary, it is confirmed that MET has a pronounced influence on the innate immune response to inflammation, which is more evident than TRP, and raises its potential to incorporate in functional feeds to be used in prophylactic strategies against predictable unfavourable events.

Immune system and immune responses in fish and their role in comparative immunity study: a model for higher organisms

The basal position of fish in vertebrate phylogeny makes them very attractive for genomic and functional comparative immunity studies. Adaptive immunity arose early in vertebrate evolution, 450 million years ago between the divergence of cyclostomes and cartilaginous fish. The fundamental immune molecules, which include Ag-recognizing lymphocytes, immunoglobulins (Abs and Ig-family TCR), MHC products, and recombination-activating (RAG) 1 and 2 genes and the recombination mechanisms (cause of diversity in TCRs and Igs) are similar in fish and mammals. These molecules and their immune response mechanisms unravelled the primordial vertebrate immune system repertoire and adaptive radiations. Moreover, screening of animal models like zebrafish has a great importance to discover genes involved in T cell development, thymic organogenesis, and in immunity to infections. The zebrafish model may also be useful for cancer research due to its various features like rapid development, tractable genetics, ease in in vivo imaging and chemical screening.

Natural history of SLC11 genes in vertebrates: tales from the fish world

BACKGROUND

The SLC11A1/Nramp1 and SLC11A2/Nramp2 genes belong to the SLC11/Nramp family of transmembrane divalent metal transporters, with SLC11A1 being associated with resistance to pathogens and SLC11A2 involved in intestinal iron uptake and transferrin-bound iron transport. Both members of the SLC11 gene family have been clearly identified in tetrapods; however SLC11A1 has never been documented in teleost fish and is believed to have been lost in this lineage during early vertebrate evolution. In the present work we characterized the SLC11 genes in teleosts and evaluated if the roles attributed to mammalian SLC11 genes are assured by other fish specific SLC11 gene members.

RESULTS

Two different SLC11 genes were isolated in the European sea bass (Dicentrarchus. labrax), and named slc11a2-α and slc11a2-β, since both were found to be evolutionary closer to tetrapods SLC11A2, through phylogenetic analysis and comparative genomics. Induction of slc11a2-α and slc11a2-β in sea bass, upon iron modulation or exposure to Photobacterium damselae spp. piscicida, was evaluated in in vivo or in vitro experimental models. Overall, slc11a2-α was found to respond only to iron deficiency in the intestine, whereas slc11a2-β was found to respond to iron overload and bacterial infection in several tissues and also in the leukocytes.

CONCLUSIONS

Our data suggests that despite the absence of slc11a1, its functions have been undertaken by one of the slc11a2 duplicated paralogs in teleost fish in a case of synfunctionalization, being involved in both iron metabolism and response to bacterial infection. This study provides, to our knowledge, the first example of this type of sub-functionalization in iron metabolism genes, illustrating how conserving the various functions of the SLC11 gene family is of crucial evolutionary importance.

Antigen-dependent T lymphocytes (TcRβ+) are primarily differentiated in the thymus rather than in other lymphoid tissues in sea bass (Dicentrarchus labrax, L.)

All jawed vertebrates share lymphocyte receptors that allow the recognition of pathogens and the discrimination between self and non-self antigens. The T cell transmembrane receptor (TcR) has a central role in the maturation and function of T lymphocytes in vertebrates via an important role in positive selection of the variable region of TcR αβ/γδ chains. In this study, the TcRβ transcript expression and TcRβ(+) cell distribution during the ontogeny of the immune system of sea bass (Dicentrarchus labrax, L.) were analysed. RT-PCR analysis of larvae during early development demonstrated that the β chain transcript is expressed by 19 days post-fertilisation (p.f.). RNA probes specific for the β chain were synthesised and used for in situ hybridisation experiments on 30 day p.f. to 180 day old juvenile larvae. A parallel immunohistochemical study was performed using the anti-T cell monoclonal antibody DLT15 developed in our laboratory [Scapigliati et al., Fish Shellfish Immunol 1996; 6:383-401]. The first thymus anlage was detectable at 32-33 days p.f. (Corresponding to about 27 days post-hatch). DLT15(+) cells were detected at day 35 p.f. in the thymus whereas TcRβ(+) cells were recognisable at day 38 p.f. in the thymus and at day 41 p.f. in the gut. TcRβ(+) cells were observed in capillaries from 41 to 80 days p.f. At day 46 p.f., TcRβ(+) cells were identified in the head kidney and were detected in the spleen 4 days later. The present results demonstrate that TcRβ(+) cells can be differentiated first in the thymus and then in other organs/tissues, suggesting potential TcRβ(+) cell colonisation from the thymus to the middle gut. Once the epithelial architecture of the thymus is completed with the formation of the cortical-medullary border (around 70-75 days p.f.), DLT15(+) cells or TcRβ(+) cells are confined mainly to the cortex and cortical-medullary border. In particular, a large influx of TcRβ(+) cells was observed at the cortical-medullary border from 72 to 90 days p.f., suggesting a role in positive selection for this thymic region during the ontogeny of the fish immune system. This study provides novel information about the primary differentiation and distribution of TcRβ(+) cells in sea bass larvae and juveniles.

A variant of the interleukin-1beta gene in European sea bass, Dicentrarchus labrax L., is associated with increased resistance against Vibrio anguillarum

Vibriosis caused by the pathogenic bacterium Vibrio (Listonella) anguillarum leads to serious losses in European sea bass, Dicentrarchus labrax. Because of its pleiotropic activity in controlling immune and inflammatory responses against various pathogens, interleukin-1beta (IL-1beta) is an attractive candidate for resistance to bacterial vibriosis. Four polymorphisms c.76 + 52C>T, c.76 + 157A>G, c.76 + 215A>and c76 + 310A>G of IL1B were genotyped in progeny of four families of wild sea bass captured in geographically distinct regions of the Black Sea and Sea of Azov and challenged with V. anguillarum. In the transmission disequilibrium test, the TGGG haplotype of IL1B showed significant overtransmission from parents to surviving progeny, thereby suggesting an association with higher resistance to V. anguillarum infection (Odds Ratio 0.38, P < 10(-7)). Using a luciferase reporter assay, we found a 1.4-fold increase in transcription activity of the protective IL1B TGGG variant compared to the susceptible CAAA variant of IL1B. The higher transcriptional activity of IL1B TGGG may arise from the functional effects of c.76 + 157A>G and c.76 + 215A>G polymorphisms disrupting potential binding sites for glucocorticoid receptor and YY1, both are negative transcription regulators.

A radiation hybrid map of the European sea bass (Dicentrarchus labrax) based on 1581 markers: Synteny analysis with model fish genomes

The selective breeding of fish for aquaculture purposes requires the understanding of the genetic basis of traits such as growth, behaviour, resistance to pathogens and sex determinism. Access to well-developed genomic resources is a prerequisite to improve the knowledge of these traits. Having this aim in mind, a radiation hybrid (RH) panel of European sea bass (Dicentrarchus labrax) was constructed from splenocytes irradiated at 3000 rad, allowing the construction of a 1581 marker RH map. A total of 1440 gene markers providing ~4400 anchors with the genomes of three-spined stickleback, medaka, pufferfish and zebrafish, helped establish synteny relationships with these model species. The identification of Conserved Segments Ordered (CSO) between sea bass and model species allows the anticipation of the position of any sea bass gene from its location in model genomes. Synteny relationships between sea bass and gilthead seabream were addressed by mapping 37 orthologous markers. The sea bass genetic linkage map was integrated in the RH map through the mapping of 141 microsatellites. We are thus able to present the first complete gene map of sea bass. It will facilitate linkage studies and the identification of candidate genes and Quantitative Trait Loci (QTL). The RH map further positions sea bass as a genetic and evolutionary model of Perciformes and supports their ongoing aquaculture expansion.

Cellular and molecular immune responses of the sea bass (Dicentrarchus labrax) experimentally infected with betanodavirus

Naïve sea bass juveniles (38.4 + or - 4.5 g) were intramuscularly infected with a sublethal dose of betanodavirus isolate 378/I03, followed after 43 days by a similar boosting. This infection resulted in an overall mortality of 7.6%. At various intervals, sampling of fish tissues was performed to investigate: i) B and T lymphocyte content in organs and tissues; ii), proliferation of leucocytes re-stimulated in vitro with inactivated virus; iii) presence of serum antibody specific for betanodavirus; iv) expression of genes coding for the following immunoregulatory molecules involved in innate and acquired responses: type I IFN, Mx, IL-1, Cox-2; IL-10, TGF-beta, TCRbeta, CD4, CD8alpha, IgM, by using a quantitative PCR array system developed for sea bass. The obtained results showed a detectable increase of T cells and B cells in PBL during betanodavirus infection. Furthermore, leucocytes obtained from blood, head kidney, and gills showed a detectable "in vitro" increase in viability upon addition of inactivated viral particles, as determined by measuring intracellular ATP concentration. ELISA analysis of sera showed that exposure to nodavirus induced a low, but specific antibody titer measured 43 days after infection, despite the presence of measurable levels of natural antibody. Finally, a strong upregulation of genes coding for type I IFN, Mx, and IgM was identified after both infection and boosting. Interestingly, an upregulation of Cox-2 until boosting, and of TGF-beta and IL-10 after boosting was also observed, while the other tested genes did not show any significant variations with respect to mock-treated fish. Overall, our work represents a first comprehensive analysis of cellular and molecular immune parameters in a fish species exposed to a pathogenic virus.

A combined AFLP and microsatellite linkage map and pilot comparative genomic analysis of European sea bass Dicentrarchus labrax L

European sea bass (Dicentrarchus labrax L., Moronidae, Teleostei) sustains a regional fishery and is commonly farmed in the Mediterranean basin, but has not undergone much long-term genetic improvement. An updated genetic linkage map of the European sea bass was constructed using 190 microsatellites, 176 amplified fragment length polymorphisms and two single nucleotide polymorphisms. From the 45 new microsatellite markers (including 31 type I markers) reported in this study, 28 were mapped. A total of 368 markers were assembled into 35 linkage groups. Among these markers, 28 represented type I (coding) markers, including those located within the peptide Y, SOX10, PXN1, ERA and TCRB genes (linkage groups 1, 7, 16, 17 and 27 respectively). The sex-averaged map spanned 1373.1 centimorgans (cM) of the genome. The female map measured 1380.0 cM, whereas the male map measured 1046.9 cM, leading to a female-to-male (F:M) recombination rate ratio of 1.32:1. The intermarker spacing of the second-generation linkage map of the European sea bass was 3.67 cM, which is smaller than that of the first-generation linkage map (5.03 cM). Comparative mapping of microsatellite flanking regions was performed with five model teleosts and this revealed a high percentage (33.6%) of evolutionarily conserved regions with the three-spined stickleback.