Immunological control of fish diseases

Probiotic supplementation influences the diversity of the intestinal microbiota during early stages of farmed senegalese sole (Solea Senegalensis, Kaup 1858)

Ingestion of bacteria at early stages results in establishment of a primary intestinal microbiota which likely undergoes several stages along fish life. The role of this intestinal microbiota regulating body functions is crucial for larval development. Probiotics have been proved to modulate this microbiota and exert antagonistic effects against fish pathogens. In the present study, we aimed to determine bacterial diversity along different developmental stages of farmed Senegalese sole (Solea senegalensis) after feeding probiotic (Shewanella putrefaciens Pdp11) supplemented diet for a short period (10-30 days after hatching, DAH). Intestinal lumen contents of sole larvae fed control and probiotic diets were collected at 23, 56, 87, and 119 DAH and DNA was amplified using 16S rDNA bacterial domain-specific primers. Amplicons obtained were separated by denaturing gradient gel electrophoresis (DGGE), cloned, and resulting sequences compared to sequences in GenBank. Results suggest that Shewanella putrefaciens Pdp11 induces a modulation of the dominant bacterial taxa of the intestinal microbiota from 23 DAH. DGGE patterns of larvae fed the probiotic diet showed a core of bands related to Lactobacillus helveticus, Pseudomonas acephalitica, Vibrio parahaemolyticus, and Shewanella genus, together with increased Vibrio genus presence. In addition, decreased number of clones related to Photobacterium damselae subsp piscicida at 23 and 56 DAH was observed in probiotic-fed larvae. A band corresponding to Shewanella putrefaciens Pdp11 was sequenced as predominant from 23 to 119 DAH samples, confirming the colonization by the probiotics. Microbiota modulation obtained via probiotics addition emerges as an effective tool to improve Solea senegalensis larviculture.

Carp edema virus/Koi sleepy disease: an emerging disease in Central-East Europe

Koi sleepy disease (KSD), also known as carp edema virus (CEV), was first reported from juvenile colour carp in Japan in the 1970s. Recently, this pox virus was detected in several European countries, including Germany, France and the Netherlands. In England, in addition to colour carp, outbreaks in common carp are reported. KSD/CEV is an emerging infectious disease characterized by a typical sleepy behaviour, enophthalmia, generalized oedematous condition and gill necrosis, leading to hypoxia. High mortality, of up to 80-100%, is seen in juvenile koi collected from infected ponds. In Austria, this disease had not been detected until now. In spring 2014, diagnostic work revealed the disease in two unrelated cases. In one instance, a pond with adult koi was affected; in the other, the disease was diagnosed in adult common carp recently imported from the Czech Republic. A survey was carried out on recent cases (2013/2014), chosen from those with similar anamnestic and physical examination findings, revealing a total of 5/22 cases positive for KSD/CEV. In this study, two paradigmatic cases are presented in detail. Results together with molecular evidence shaped the pattern of the first diagnosis of KSD/CEV in fish from Austrian ponds. In the light of the positive cases detected from archived material, and the spread of the disease through live stock, imported from a neighbouring country, the need for epidemiological investigations in Austria and surrounding countries is emphasized.

Effect of temperature and short chain fructooligosaccharides supplementation on the hepatic oxidative status and immune response of turbot (Scophthalmus maximus)

In this study the effect of diet supplementation with different levels of short-chain fructooligosaccharides (scFOS) on the hepatic oxidative status, hematology and innate immune parameters was evaluated in turbot reared at 15 °C and 20 °C. Four practical diets containing half of the protein provided by plant ingredients and the other half by fish meal were supplemented with scFOS at 0%, 0.5%, 1.0% and 2.0% and fed to turbot juveniles for 9 weeks. Independently of the rearing temperature, diet with 1% scFOS increased the haematocrit (Ht) while 2% scFOS augmented the mean corpuscular haemoglobin concentration (MCHC). Mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), white blood cells (%) and lysozyme were higher in fish reared at 15 °C, whereas red blood cells and neutrophil numbers increased in fish reared at 20 °C. Catalase (CAT) and glutathione peroxidase (GPX) activities were affected by rearing temperature being lower in fish reared at 20 °C. Compared to the control diet, at 15 °C, turbot fed 0.5 or 1% scFOS presented lower activities of CAT and glutathione reductase (GR). At 20 °C turbot fed the 2% scFOS diet presented lower activities of CAT and GPX. Lipid peroxidation (LPO) and glucose 6-phosphate dehydrogenase (G6PDH) activity were not affected by temperature nor dietary prebiotic incorporation. Results of this study suggest scFOS has no effect on innate immunology or hematology. High temperature (20 °C) does not induce turbot oxidative stress, but the recommended dietary scFOS incorporation level for counteracting oxidative stress may differ with other rearing temperature.

Study of the bile proteome of Atlantic cod (Gadus morhua): Multi-biological markers of exposure to polycyclic aromatic hydrocarbons

PAH metabolites present in bile are well-known biological markers of exposure in fish, and their investigation is recommended by the ICES (International Council for the Exploration of the Sea) and the OSPAR convention (Convention for the Protection of the Marine Environment of the North-East Atlantic) for monitoring purposes. Development of analytical strategies for fish bile is encouraged by the need for more sensitive and informative markers (e.g., capable of tracking the PAH composition of contamination sources) and strengthened by recent results in both fish genomics and proteomics. Herein, the study of the Atlantic cod bile proteome is presented. Preliminary testing for discovering new sensitive markers in the form of expressed proteins affected by PAH exposure (i.e., PAH-protein adducts) is reported. Protein markers were identified using LC-MS/MS analysis, as single biological indicators. Through multivariate analyses, the overall proteome was revealed to be a sensitive multi-biological marker of exposure to PAHs.

Molecular cloning and characterization of secretory and membrane-bound IgM of turbot

In recent years, increasing diseases especially bacterial diseases have brought a host of losses with the expansive cultivation of turbot (Scophthalmus maximus). In order to do more research about the immune system of turbot for better understanding the mechanism of resisting diseases, the immunoglobulin genes related to secretory and membrane-bound IgM (s-IgM and m-IgM) of turbot were cloned using homology sequences cloning and SMART RACE PCR method. The heavy chain of s-IgM cDNA is 1900 bp in length including a leader region, a variable region, four constant regions (CH1, CH2, CH3 and CH4) and a C-terminal while the cDNA of m-IgM is 1795 bp with the same leader region, variable region, three constant regions (CH1, CH2 and CH3) and two transmembrane regions (TM1 and TM2). The sequence of IgM gene was also obtained and the structure consisted of V-CH1-CH2-CH3-CH4-TM1-TM2 is similar to other fishes. The highest level of s-IgM expression was observed in spleen, followed by kidney, gills, eyes, skin of the healthy turbot whereas the same profile of m-IgM expression is found with low level. And s-IgM takes up dominant proportion of total IgM expression. Also the relative expressions of s-IgM and m-IgM were analyzed in turbot vaccinated with the live attenuated vaccine Vibrio anguillarum. Not only the transcriptions of both s-IgM and m-IgM in liver, spleen and kidney of turbot injected with V. anguillarum MVAV6203 were up-regulated but also the expressions of s-IgM and m-IgM in spleen, kidney, gut, skin and gills of bath-vaccinated turbot were increased. Comparing the ratio changes of relative expression of m-IgM and s-IgM in vaccinated turbot, we found that the proportion of m-IgM were increasing in both administration routes, which probably indicated that the increasing expression of m-IgM strengthen the phagocytic ability of B cells.

Analysis of immune-related ESTs and differential expression analysis of few important genes in lines of rohu (Labeo rohita) selected for resistance and susceptibility to Aeromonas hydrophila infection

A total of 137,629 contigs generated via de novo transcriptome assembly from resistant and susceptible lines of rohu (first generation) raised against aeromoniasis were further analyzed in terms of defence-related genes. Out of 1,939 contigs showing homology to genes involved in immune processes, 1,866 were further categorised into different functional subgroups. Comparative analysis revealed five genes for the first time in any carp species out of which apolipoprotein h, septin 4 isoform 3 and septin isoform cra_c were identified for the first time in fish. Differential expression analysis of ten genes viz., heat shock proteins (Hsps) (Hsp30, Hsp70 and Hsp90), serum lectin isoform 1 (SLI1), linker histone H1M (LHH1M), NAD(P)H quinone 1 (NQO1), zona pellucida 2 (ZP2) and three unknown genes that were highly up-expressed in first generation resistant line fish from mRNA-seq coverage data, was carried out using susceptible and resistant individuals of the second generation selected populations in eight different tissues viz. liver, kidney, intestine, gill, brain, spleen, skin and muscle using qPCR. Significant up-regulation in Hsp90, NQO1, C_116914 and C_22454 in specific tissues of resistant line and variable expression in Hsp30 and LHH1M genes in different tissues of both lines were noticed. The expression of Hsp70 was lower in many tissues of the resistant line than in susceptible line rohu. The expression of ZP2, SLI1 and C_94589 genes was not significantly different in terms of fold difference between the two lines. Differentially expressed genes need further characterisation to explore their role in resistance to Aeromonas hydrophila infection in rohu.

Effect of dietary supplementation of probiotics and palm fruits extracts on the antioxidant enzyme gene expression in the mucosae of gilthead seabream (Sparus aurata L.)

Antioxidant activity is particularly important, since oxidation is an unavoidable reaction in all living bodies. At present, natural antioxidants to be used on food as an alternative to synthetic ones are being sought. Gilthead seabream (Sparus aurata L.) specimens were fed for 4 weeks with diets enriched with bacterial probiotics (Shewanella putrefaciens Pdp11 and Bacillus sp), single or in combination with Tunisian dates palm fruit extracts. The expression of the main antioxidant enzyme genes (superoxide dismutase, catalase and glutathione reductase) in the mucosae (gut, skin and gill) was evaluated after 2 and 4 weeks. Previously, free radical scavenging and several antioxidant assays were developed to know the antioxidant properties present on the palm fruits extracts. The results demonstrated that experimental diets alter the expression of the studied antioxidant genes, primarily in the gill and skin. Furthermore, the tested probiotics and mainly, the aqueous date palm fruits extracts had significant antioxidant properties based on their protective effect against the levels of intracellular reactive oxygen species, especially when administering during 4 weeks. For this reason, probiotics and date palm fruit extracts may serve as good natural antioxidants and could potentially be considered as a functional food ingredient for fish in farms.

Chronic stress due to high stocking density in open sea cage farming induces variation in biochemical and immunological functions in Asian seabass (Lates calcarifer, Bloch)

Stocking density is an important factor in cage aquaculture of finfish. Effects of high stocking density (35 fish cubic m(-1)) on a range of biochemical and immunological parameters in Asian seabass reared in open sea floating net cages were compared to fish held in relatively low density (15 fish cubic m(-1)). The results revealed that chronic stress due to high stocking density induced variations in most of the parameters studied as evidenced by increased cortisol and glucose levels and decreased activity of lysozyme, myeloperoxidase and complement. Production of reactive oxygen species, total leucocyte count and total serum protein were also decreased, whereas anti-protease, alkaline phosphatase and acid phosphatase activities were increased in high stocking-density group when compared to low stocking-density group. Effects of chronic stress due to high stocking density were discussed in relation to variations in these parameters.

Cloning and characterization of the Mx1, Mx2 and Mx3 promoters from gilthead seabream (Sparus aurata)

Mx proteins are main effectors of the antiviral innate immune response mediated by type I interferon (IFN I). Actually, diverse Mx proteins from fish proved highly active against fish viruses, standing out among them the Mx1, Mx2 and Mx3 from gilthead seabream (Sparus aurata), a species exhibiting a natural resistance to viral diseases. In this study, the structure and functional activity of their corresponding promoters (pMx1, pMx2 and pMx3) have been assessed. The three promoters present an identical 3' region of 157 bp, exhibiting a single canonical interferon-stimulated response element (ISRE), which is indispensible for the poli:IC induction of pMx1 and pMx3, while not for that of pMx2. In the remaining part of the three promoters other regulatory motifs were identified, as gamma IFN activated sites in variable number (1, 4 and 2 in pMx1, pMx2 and pMx3, respectively), as well as several independent GAAA elements or ISRE core sequences (13, 15 and 12 in pMx1, pMx2 and pMx3, respectively). The structural dissimilarities shown by the three promoters parallels with the differences observed in their response profiles, in terms of the time course of the induction, and basal and induced expression levels of each promoter. Altogether, these findings indicate that the expression of Mx1, Mx2 and Mx3 genes from the gilthead seabream might be specifically regulated, in accordance with the functional role of each Mx protein in the successful antiviral response shown by this species.

Probiotics in fish and shellfish culture: immunomodulatory and ecophysiological responses

Aquaculture is emerging as one of the most viable and promising enterprises for keeping pace with the surging need for animal protein, providing nutritional and food security to humans, particularly those residing in regions where livestock is relatively scarce. With every step toward intensification of aquaculture practices, there is an increase in the stress level in the animal as well as the environment. Hence, disease outbreak is being increasingly recognized as one of the most important constraints to aquaculture production in many countries, including India. Conventionally, the disease control in aquaculture has relied on the use of chemical compounds and antibiotics. The development of non-antibiotic and environmentally friendly agents is one of the key factors for health management in aquaculture. Consequently, with the emerging need for environmentally friendly aquaculture, the use of alternatives to antibiotic growth promoters in fish nutrition is now widely accepted. In recent years, probiotics have taken center stage and are being used as an unconventional approach that has numerous beneficial effects in fish and shellfish culture: improved activity of gastrointestinal microbiota and enhanced immune status, disease resistance, survival, feed utilization and growth performance. As natural products, probiotics have much potential to increase the efficiency and sustainability of aquaculture production. Therefore, comprehensive research to fully characterize the intestinal microbiota of prominent fish species, mechanisms of action of probiotics and their effects on the intestinal ecosystem, immunity, fish health and performance is reasonable. This review highlights the classifications and applications of probiotics in aquaculture. The review also summarizes the advancement and research highlights of the probiotic status and mode of action, which are of great significance from an ecofriendly, sustainable, intensive aquaculture point of view.

Modulation of cellular innate immunity by Lepeophtheirus salmonis secretory products

Lepeophtheirus salmonis produces pharmacologically active substances that have been shown to modify genetic expression of inflammatory mediators in SHK-1 cells and head kidney macrophages of salmon. Differences in genetic expression among genera of Oncorhynchus and Salmo reflect different susceptibilities to L. salmonis. This study was conducted to determine if the presence of L. salmonis secretory products (SEPs)(1) alters the cellular innate immune response (specifically macrophage function) among several salmonids. Phagocytic assays were performed using SHK-1 cells and macrophages isolated from pink (Oncorhynchus gorbuscha), chum (Oncorhynchus keta) and Atlantic (Salmo salar) salmon following incubation with SEPs and Aeromonas salmonicida. Respiratory burst assays were analyzed using pink, chum and Atlantic salmon macrophages after exposure to SEPs. For SHK-1 cells, incubation with SEPS led to dose-dependent increases in phagocytosis. Following incubation with SEPs, chum salmon macrophages had the highest phagocytic index (55.1%) followed by Atlantic (26.4%) and pink (15.8%) salmon. In contrast, respiratory burst response was greatest in pink salmon and minimal in the other two species. Our results suggest that the cellular innate immune response of salmon is modified in the presence of L. salmonis secretions and differences observed among species provide insight into species-specific consequences of sea lice infection.

Gram-negative marine bacteria: structural features of lipopolysaccharides and their relevance for economically important diseases

Gram-negative marine bacteria can thrive in harsh oceanic conditions, partly because of the structural diversity of the cell wall and its components, particularly lipopolysaccharide (LPS). LPS is composed of three main parts, an O-antigen, lipid A, and a core region, all of which display immense structural variations among different bacterial species. These components not only provide cell integrity but also elicit an immune response in the host, which ranges from other marine organisms to humans. Toll-like receptor 4 and its homologs are the dedicated receptors that detect LPS and trigger the immune system to respond, often causing a wide variety of inflammatory diseases and even death. This review describes the structural organization of selected LPSes and their association with economically important diseases in marine organisms. In addition, the potential therapeutic use of LPS as an immune adjuvant in different diseases is highlighted.

Co-infection of Atlantic salmon (Salmo salar), by Moritella viscosa and Aliivibrio wodanis, development of disease and host colonization

Two species of bacteria are repeatedly isolated from farmed fish with winter-ulcer disease. Moritella viscosa is the aetiological agent of the disease; the significance of Aliivibrio wodanis is uncertain but has not been related to the primary pathogenesis. A cell culture infection model showed that A. wodanis adhered to, but did not invade the fish cells. Exposure to culture supernatant of A. wodanis caused the fish cells to vacoulate, retract, round up and detach from the surface, and rearrange the actin filaments of the cytoskeleton. These observations suggest that the bacterium secretes toxins into the extracellular environment. Any pathologic effect of A. wodanis and the effect of co-culturing with M. viscosa was studied in Atlantic salmon (Salmo salar) bath challenged with; only M. viscosa or only A. wodanis or both bacteria together. Both M. viscosa and A. wodanis were re-isolated from external surfaces and internal organs from live and deceased co-infected fish. It is further hypothesized that A. wodanis colonization might influence the progression of a M. viscosa infection. This is to our knowledge the first study that reproduces field observations where both bacteria infect Atlantic salmon.

Comparative skin mucus and serum humoral defence mechanisms in the teleost gilthead seabream (Sparus aurata)

Mucosal surfaces of fish, including skin, gill and gut, contain numerous immune substances poorly studied that act as the first line of defence against a broad spectrum of pathogens. This study aimed to identify and characterize for the first time different constitutive humoral defence mechanisms of the skin mucus of gilthead seabream (Sparus aurata). To do this, the levels of total immunoglobulin M, several enzymes and proteins (peroxidase, lysozyme, alkaline phosphatase, esterases, proteases and antiproteases), as well as the bactericidal activity against opportunist fish pathogens (Vibrio harveyi, Vibrio angillarum, Photobacterium damselae) and non-pathogenic bacteria (Escherichia coli, Bacillus subtilis) were measured in the skin mucus and compared with those found in the serum. This study demonstrates that gilthead seabream skin mucus contains lower levels of IgM, similar levels of lysozyme, alkaline phosphatase and proteases, and higher esterase, peroxidase and antiprotease activities than serum. In addition, skin mucus revealed stronger bactericidal activity against tested fish pathogen bacteria compared to the serum activity, while human bacteria can even grow more in the presence of mucus. The results could be useful for better understanding the role of the skin mucus as a key component of the innate immune system with potential application for the aquaculture.

Functional analysis of a dietary recombinant fatty acid binding protein 10 (FABP10) on the Epinephelus coioides in response to acute low temperature challenge

The effect of Ec-FABP10 (Epinephelus coiodes-FABP10) on growth performance, enzyme activity, respiratory burst, MDA level, ATP content, immune-related gene expression of juvenile orange-spotted grouper (E. coioides). The commercial diet supplemented with FABP10 protein was feed to orange-spotted grouper for six weeks. No significant difference was observed in the specific growth rates, while the survival rate in the FABP10 additive group was significantly higher. After the feeding trial, the groupers were exposed to acute low temperature challenge. The decreased level of respiratory burst activity was observed in the FABP10 additive group after the exposure to the acute low temperature stress, while the blood cell count increased significantly at 15 °C and a significant increase of ATP content was observed at 10 °C. Higher enzymatic activities of CAT and SOD were observed at 20 °C and 15 °C, respectively. Meanwhile, the lower level of MDA was observed after the exposure to acute low temperature challenge by comparing with the controls. Further transcript expression analyses of FABP10, SOD2, GPX4, HSPA4 and LIPC in liver by quantitative real-time PCR demonstrated that the up-regulated transcript expression of FABP10, SOD2, HSPA4 and LIPC was observed in FABP10 additive group at 15 °C, while the transcript expression of GPX4 increased significantly at 20 °C. Western blotting analysis confirmed that FABP10 protein expression strongly increased at 15 ± 0.5 °C in FABP10 additive group. These results showed that FABP10 additive diet could moderate the metabolic and immune abilities mainly via ROS pathway in the orange-spotted grouper.

A fibrinogen-related protein (TfFREP2) gene involving in the immune response of Trachidermus fasciatus against Vibrio anguillarum

Fibrinogen-related proteins play important roles in the immune responses. We have obtained a cDNA encoding a novel fibrinogen-related protein from roughskin sculpin Trachidermus fasciatus (T. fasciatus) and named it as TfFREP2. The N and C terminus of TfFREP2 contain a putative 21-amino acid signal peptide and a typical 217-amino acid fibrinogen-like domain, which is conserved in all fibrinogen-related proteins. TfFREP2 has three glycosylation sites and two potential calcium-binding sites that are possibly involved in calcium coordination. The results of tissue specific checking showed that the mRNA and protein of TfFREP2 were particularly abundant in skin and gill among all the tested tissues. TfFREP2 mRNA and protein expression changed significantly after being challenged by Vibrio anguillarum pathogen in those immune-barrier tissues, such as skin and gill. Furthermore, recombinant TfFREP2 is able to agglutinate and bind V. anguillarum in the presence of calcium ion. The above results suggest that TfFREP2 might be involved in the host defense of fish against V. anguillarum infection.

Immunomodulatory effects of the aromatic geranyl derivative filifolinone tested by the induction of cytokine expression

Fish farming crops are constantly exposed to infectious diseases due to intensive production conditions under which microorganisms develop and spread easily, resulting in severe economic losses. The massive use of antibiotics to control these diseases has lead to the accumulation of residues and the development of drug resistance. Consequently, it is urgent to develop new pharmacological tools to stimulate protective immune responses in salmonids to combat infectious diseases. We evaluated the immunostimulant activity of terpenoid derivatives isolated from species of the Heliotropium genus, which had previously shown antiviral activity in salmon. The immunomodulatory effects of the 3 H-spiro [1-benzofuran-2,1'-ciclohexane] derivative called filifolinone, were studied in vitro using the SHK-1 cell line derived from leucocytes of salmon head kidney and in vivo in Atlantic salmon. For the evaluation, we studied the effect of this compound in the expression of various cytokines. The results showed that Filifolinone increases the levels of expression of pro-inflammatory and anti-inflammatory cytokines. This suggests that Filifolinone is a potential alternative immunomodulator for veterinary purposes.

Status and future perspectives of vaccines for industrialised fin-fish farming

Fin fish farming is developing from extensive to intensive high industrial scale production. Production of fish in high-density growth conditions requires effective vaccines in order to control persistent and emerging diseases. Vaccines can also have significant positive impact on the reduced usage of antibiotics. This was demonstrated when vaccines were introduced in Norway for Atlantic salmon (Salmo salar) in the late eighties and early nineties, resulting in a rapid decline of antibiotics consumption. The present review will focus on current vaccine applications for farmed industrialized fish species such as Atlantic salmon, coho salmon (Oncorhynchus kisutch), rainbow trout (Oncorhynchus mykiss), ayu (Plecoglossus altivelis), cod (Gadus morhua), sea bass (Dicentrarchus labrax), gilt-head sea bream (Sparus aurata), yellowtail (Seriola quinqueradiata), great amberjack (Seriola dumerili), barramundi (Lates calcarifer), japanese flounder (Paralichythys olivaceus), turbot (Scophthalmus maximus), red sea bream (Pagrus major), rock bream (Oplegnathus fasciatus), seven band grouper (Epinephelus septemfasciatus), striped catfish (Pangasianodon hypophthalmus), channel catfish (Ictalurus punctatus) and tilapia (Oreochromis niloticus). This paper will review the current use of licensed vaccines in fin fish farming and describe vaccine administration regimes including immersion, oral and injection vaccination. Future trends for inactivated-, live attenuated - and DNA - vaccines will also be discussed.

Impact of Ichthyophonus infection on spawning success of Yukon River Chinook salmon Oncorhynchus tshawytscha

We examined the impacts of Ichthyophonus infection on spawning success of Yukon River Chinook salmon Oncorhynchus tshawytscha at spawning grounds of the Chena and Salcha Rivers, Alaska, USA. During the period 2005 to 2006, 1281 salmon carcasses (628 male, 652 female) were collected throughout the spawning season and from the entire spawning reaches of the Chena and Salcha Rivers. For each fish, infection status was determined by culture method and visual inspection of lesions of heart tissue as uninfected (culture negative), infected without lesions (culture positive with no visible lesions), and infected with lesions (culture positive with visible lesions), and spawning status was determined by visually inspecting the percentage of gametes remaining as full-spawned (<10%), partial-spawned (10-50%), and unspawned (>50%). Among the 3 groups, the proportion of full-spawned (i.e. spawning success) females was lower for those infected without lesions (69%) than those uninfected (87%) and infected with lesions (86%), but this did not apply to males (uninfected 42%, infected without lesions 38%, infected with lesions 41%). At the population level, the combined (infected and uninfected) proportion of female spawning success was 86%, compared to 87% when all females were assumed uninfected. These data suggest that while Ichthyophonus infection slightly reduces spawning success of infected females, its impact on the spawning population as a whole appears minimal.

Combined effects of dietary fructooligosaccharide and Bacillus licheniformis on innate immunity, antioxidant capability and disease resistance of triangular bream (Megalobrama terminalis)

This study was conducted to investigate the effects of fructooligosaccharide (FOS) and Bacillus licheniformis (B. licheniformis) and their interaction on innate immunity, antioxidant capability and disease resistance of triangular bream Megalobrama terminalis (average initial weight 30.5 ± 0.5 g). Nine experimental diets were formulated to contain three FOS levels (0, 0.3% and 0.6%) and three B. licheniformis levels (0, 1 × 10(7), 5 × 10(7) CFU g(-1)) according to a 3 × 3 factorial design. At the end of the 8-week feeding trial, fish were challenged by Aeromonas hydrophila (A. hydrophila) and survival rate was recorded for the next 7 days. The results showed that leucocyte counts, alternative complement activity as well as total serum protein and globulin contents all increased significantly (P < 0.05) as dietary B. licheniformis levels increased from 0 to 1 × 10(7) CFU g(-1), while little difference (P > 0.05) was observed in these parameters in terms of dietary FOS levels. Both plasma alkaline phosphatase and phenoloxidase activities were significantly (P < 0.05) affected only by dietary FOS levels with the highest values observed in fish fed 0.6 and 0.3% FOS, respectively. Both immunoglobulin M content and liver superoxide dismutase (SOD) activity were significantly affected (P > 0.05) by both FOS and B. licheniformis. Liver catalase, glutathione peroxidase as well as plasma SOD activities of fish fed 1 × 10(7) CFU g(-1)B. licheniformis were all significantly (P < 0.05) higher than that of the other groups, whereas the opposite was true for malondialdehyde content. After A. hydrophila challenge, survival rate was not affected (P > 0.05) by either FOS levels or B. licheniformis contents, whereas a significant (P < 0.05) interaction between these two substances was observed with the highest value observed in fish fed 0.3% FOS and 1 × 10(7) CFU g(-1)B. licheniformis. The results of this study indicated that dietary FOS and B. licheniformis could significantly enhance the innate immunity and antioxidant capability of triangular bream, as well as improve its disease resistance. The best combination of these two prebiotics and/or probiotics was 0.3% FOS and 1 × 10(7) CFU g(-1)B. licheniformis.

Genotype-specific vs. cross-reactive host immunity against a macroparasite

Vertebrate hosts often defend themselves against several co-infecting parasite genotypes simultaneously. This has important implications for the ecological dynamics and the evolution of host defence systems and parasite strategies. For example, it can drive the specificity of the adaptive immune system towards high genotype-specificity or cross-reactivity against several parasite genotypes depending on the sequence and probability of re-infections. However, to date, there is very little evidence on these interactions outside mammalian disease literature. In this study we asked whether genotype-specific or cross-reactive responses dominate in the adaptive immune system of a fish host towards a common macroparasite. In other words, we investigated if the infection success of a parasite genotype is influenced by the immunization genotype. We reciprocally immunized and re-exposed rainbow trout (Oncorhynchus mykiss) to a range of genotypes of the trematode eye fluke Diplostomum pseudospathaceum, and measured infection success of the parasite. We found that the infection success of the parasite genotypes in the re-exposure did not depend on the immunization genotype. While immunization reduced average infection success by 31%, the reduction was not larger against the initial immunization genotype. Our results suggest significant cross-reactivity, which may be advantageous for the host in genetically diverse re-exposures and have significant evolutionary implications for parasite strategies. Overall, our study is among the first to demonstrate cross-reactivity of adaptive immunity against genetically diverse macroparasites with complex life cycles.

Characterization of PAMP/PRR interactions in European eel (Anguilla anguilla) macrophage-like primary cell cultures

The eel (Anguilla anguilla) has been identified as a vulnerable species with stocks dramatically declining over the past decade. In an effort to support the species from overfishing of wild stocks increased interest in eel aquaculture has been notable. In order to expand the scarce knowledge concerning the biology of this species significant research efforts are required in several fields of biology. The development of cell culture systems to study the immune response is a key step towards an increased understanding of the immune response and to develop resources to support further study in this threatened species. Macrophages are one of the most important effector cells of the innate immune system. The capacity to engulf pathogens and orchestrate the immune response relies on the existence of different surface receptors, such as scavenger receptors and toll-like receptors. We have developed and described an eel macrophage-like in vitro model and studied its functional and transcriptomic responses. Macrophage-like cells from both head kidney and purified peripheral blood leukocytes were obtained and phagocytic activity measured for different whole bacteria and yeast. Moreover, based on PAMP-PRR association the innate immune response of both head kidney and PBL derived macrophage-like cells was evaluated against different pathogen-associated molecular patterns (PAMPs). Results highlight that peptidoglycan stimulation strongly induces inflammatory mRNA expression reflected in the up-regulation of pro-inflammatory genes IL1β and IL18 in PBL derived cells whereas IL8 is upregulated in head kidney derived cells. Furthermore TLR2 mRNA abundance is regulated by all stimuli supporting a multifunctional role for this pathogen recognition receptor (PRR) in eel macrophage-like cells.

Innate and adaptive immune responses of Arctic charr (Salvelinus alpinus, L.) during infection with Aeromonas salmonicida subsp. achromogenes and the effect of the AsaP1 toxin

Aeromonas salmonicida subsp. achromogenes, the causative agent of atypical furunculosis in many fish species, secretes the toxic metalloendopeptidase AsaP1. This study aimed to analyze innate and adaptive immune parameters induced in Arctic charr (Salvelinus alpinus, L.) infected with wild type (wt) A. salmonicida subsp. achromogenes and its isogenic asaP1 deletion mutant (AsaP1-deficient). Head-kidney, liver and spleen were obtained from i.p. infected charr (wt, AsaP1-deficient), during a time schedule of 7 d post infection. Reverse transcription quantitative real-time PCR (RT-qPCR) was applied to study the expression of immune parameters: pro-inflammatory cytokines IL-1β and TNF-α; anti-inflammatory cytokine IL-10; chemokines CXCL-8 (IL-8) and CC-chemokine; the cytokines IFN-γ and IL-4/13A as tracers for Th1 and Th2 immune responses, respectively; and the cell markers CD8α and CD83. In addition, lymphoid organs were histopathologically examined at days 3 and 7 post infection, including B (IgM) and T (CD3ε) cell staining. The detected immune responses were initially driven by innate mechanisms represented by the up-regulation of pro-inflammatory cytokines and chemokines and later on by adaptive Th2 related responses cumulating in B-cell recruitment as shown by regulation of immune parameters in spleen and head-kidney, with significant differences between mutant and wt infected fish. Histological sections revealed IgM-positive cells around ellipsoid arterioles in spleen, while CD3ε positive cells were found in clusters scattered all over the section. However, histopathological differences were only detected between infected and non-infected fish, but not between AsaP1-deficient mutant and wt infected fish. This work represents the first study on innate and adaptive immune responses of Arctic charr induced by a bacterial infection.

Fish cell cultures as in vitro models of inflammatory responses elicited by immunostimulants. Expression of regulatory genes of the innate immune response

We report the differential expression of various genes related to the regulation of the innate immune responses, including pro-inflammatory (IL-1β1, IL-8, TNF-α1, TNF-α2) and immune-suppressing (IL-10) cytokines, interferon-induced Mx-1 protein, enzymes regulating nitric oxide (inducible nitric oxide synthase, arginase-2) and eicosanoid (COX-2) production, and Toll-like pathogen pattern-recognition receptors TLR-3, TLR-5 and TLR-9, in two lympho-haematopoietic stromal cell lines derived from the spleen (trout splenic stroma, TSS) and the pronephros (trout pronephric stroma-2, TPS-2) of rainbow trout (Oncorhynchus mykiss), as well as in primary cultures of rainbow trout head kidney macrophages, after their exposure to the well-known immunostimulants LPS, levamisole and poly I:C. Although there were differences in the responses between the two stromal cell lines, using reverse transcription followed by real time polymerase chain reaction (RT-qPCR) we demonstrated that exposure to the immunostimulants, particularly poly I:C and LPS, resulted in significant changes in the expression of the immunoregulatory genes in the two stromal cell lines in many cases their responses resembling in fold change magnitudes and in response profiles to those observed in the primary macrophage cultures. Exposure to poly I:C and, with lower fold change values, to LPS produced upregulation of the pro- (IL-1β, IL-8, TNF-α) and anti-inflammatory (IL-10) cytokine genes, as well as of the Mx-1 gene. Furthermore, the immunostimulation elicited the upregulation of COX-2, iNOS and arginase-2 genes in the cell lines. Likewise, the TSS and TPS-2 cell lines significantly upregulated the expression of TLR-3, TLR-5 and TLR-9 genes after exposure to the immunostimulants, thus explaining the ability of the stromal cells to recognise and respond to the immunostimulants. Such results give support to an important role of lympho-haematopoietic stromal cells in the development and control of pro-inflammatory responses in fish. The upregulation of genes of pro-inflammatory cytokines and of mediators of the innate immune responses correlates well with the previously demonstrated functional capacities, including phagocytosis, microbicidal activity and NO production, exhibited by the TSS and TPS-2 stromal cell lines when exposed to the same immunostimulants. On the other hand, the expression of immunosuppressing genes (IL-10, COX-2 and arginase-2) demonstrate that the lympho-haematopoietic stromal cells are also able to contribute to the control of inflammatory responses. This study reinforce the possibility of using histotypic cell cultures, as those formed by the TSS and TPS-2 cell lines, formed by heterogeneous cell populations that partially replicates the cell-cell and cell-extracellular matrix interactions, to develop cost-effective and repetitive in vitro systems for the screening of immunostimulant candidates for aquaculture, as they are able to replicate in vitro immune regulatory networks occurring in vivo.

Differential regulation of cathelicidin in salmon and cod

Antimicrobial peptides (AMPs) are an important component of innate immunity in vertebrates. The cathelicidin family of AMPs is well characterized in mammals and has also been reported in several fish species. In this study we investigated the regulation of cathelicidin expression in a gadoid and a salmonid cell-line in order to dissect the signalling pathways involved. For this, fish cells were treated with microbial lysates, purified microbial components and commercial signalling inhibitors and expression of cathelicidin was assessed with quantitative real-time PCR (qPCR). We found that cathelicidin expression was induced in both cell lines in response to microbial stimuli, but the response patterns differed in these evolutionary distant fish species. Our data suggest that in salmonids, pattern recognition receptors such as TLR5 may be involved in the stimulation of cathelicidin expression and that the signalling cascade can include PI3-kinase and cellular trafficking compartments. A detailed knowledge of the regulating factors involved in AMP-related defence responses, including cathelicidin, could help in developing strategies to enhance the immune defence of fish.

Differentiation at the MHCIIα and Cath2 loci in sympatric Salvelinus alpinus resource morphs in Lake Thingvallavatn

Northern freshwater fish may be suitable for the genetic dissection of ecological traits because they invaded new habitats after the last ice age (∼10.000 years ago). Arctic charr (Salvelinus alpinus) colonizing streams and lakes in Iceland gave rise to multiple populations of small benthic morphotypes, often in sympatry with a pelagic morphotype. Earlier studies have revealed significant, but subtle, genetic differentiation between the three most common morphs in Lake Thingvallavatn. We conducted a population genetic screen on four immunological candidate genes Cathelicidin 2 (Cath2), Hepcidin (Hamp), Liver expressed antimicrobial peptide 2a (Leap-2a), and Major Histocompatibility Complex IIα (MHCIIα) and a mitochondrial marker (D-loop) among the three most common Lake Thingvallavatn charr morphs. Significant differences in allele frequencies were found between morphs at the Cath2 and MHCIIα loci. No such signal was detected in the D-loop nor in the other two immunological genes. In Cath2 the small benthic morph deviated from the other two (FST  = 0.13), one of the substitutions detected constituting an amino acid replacement polymorphism in the antimicrobial peptide. A more striking difference was found in the MHCIIα. Two haplotypes were very common in the lake, and their frequency differed greatly between the morphotypes (from 22% to 93.5%, FST  = 0.67). We then expanded our study by surveying the variation in Cath2 and MHCIIα in 9 Arctic charr populations from around Iceland. The populations varied greatly in terms of allele frequencies at Cath2, but the variation did not correlate with morphotype. At the MHCIIα locus, the variation was nearly identical to the variation in the two benthic morphs of Lake Thingvallavatn. The results are consistent with a scenario where parts of the immune systems have diverged substantially among Arctic charr populations in Iceland, after colonizing the island ∼10.000 years ago.

Gene expression profiling in live attenuated Edwardsiella tarda vaccine immunized and challenged zebrafish: insights into the basic mechanisms of protection seen in immunized fish

Despite the importance and success of vaccine immunization against bacterial diseases in fish, little is known about the molecular mechanisms of vaccine-induced immune protection in teleost fish. In this study, the live attenuated Edwardsiella tarda vaccine strain WED, which has been shown to evoke efficacious protection against edwardsiellosis and ascites diseases in fish, was extensively evaluated for multiple parameters in a 5-week immunization and challenge experiment in zebrafish. The parameters evaluated included the immunologic potency (relative percent survival, RPS), the specific IgM antibody titers and the expression profiles of multiple immune-related gene markers at multiple time points following immunization and challenge. During the 4-week immunization phase, the toll-like receptor (TLR) 5 signaling pathway, the MHC-I antigen processing pathway and cytotoxic T lymphocyte (CTL) responses were activated in succession. In contrast, the MHC-II antigen processing pathway and the markers of CD4(+) T lymphocyte activation were down-regulated, and IgM transcription and specific IgM antibody titers were not significantly induced following immunization. During the 1-week challenge phase, the induction of MHC-I and CTL responses and the inhibition of MHC-II and CD4(+) T cell responses were similarly observed in immunized zebrafish following challenge with wild E. tarda. With the 5-week immunization and challenge model, our data suggest the basic mechanism that underlying the long-lasting protective immunity elicited by WED in zebrafish. This mechanism involved the induction of the TLR-5 signaling pathway, the MHC-I antigen processing pathway and CTL effector function, and CTL function seems play a major role in the protection against E. tarda infection in zebrafish.

Beta-glucan: an ideal immunostimulant in aquaculture (a review)

The major hindrance in the development and sustainability of aquaculture industry is the occurrence of various diseases in the farming systems. Today, preventive and management measures are central concern to overcome such outbreak of diseases. Immunostimulants are considered as an effective tool for enhancing immune status of cultured organisms. Among different immunostimulants used in aquaculture practices, β-glucan is one of the promising immunostimulant, which is a homopolysaccharide of glucose molecule linked by the glycoside bond. It forms the major constituents of cell wall of some plants, fungi, bacteria, mushroom, yeast, and seaweeds. Major attention on β-glucan was captivated with the gain in knowledge on its receptors and the mechanism of action. The receptor present inside the animal body recognizes and binds to β-glucan, which in turn renders the animal with high resistance and enhanced immune response. This review highlights β-glucan as an immunostimulant, its effective dosages, and route of administration and furthermore provides an outline on role of β-glucan in enhancing growth, survival, and protection against infectious pathogens pertaining to fishes and shellfishes. Study also summarizes the effect of β-glucan on its receptors, recognition of proteins, immune-related enzymes, immune-related gene expression and their mechanisms of action.

Changes in intestinal morphology and microbiota caused by dietary administration of inulin and Bacillus subtilis in gilthead sea bream (Sparus aurata L.) specimens

Changes produced in gilthead sea bream (Sparus aurata L.) intestinal morphology and microbiota caused by dietary administration of inulin and Bacillus subtilis have been studied. Gilthead sea bream specimens were fed diets containing 0 (control), inulin (10 g kg(-1)), B. subtilis (10(7) cfu g(-1)), or B. subtilis + inulin (10(7) cfu g(-1) + 10 g kg(-1)) for four weeks. Curiously, fish fed the experimental diets (inulin, B. subtilis, or B. subtilis + inulin) showed the same morphological alterations when studied by light and electron microscopy, while significant differences in the signs of intestinal damage were detected by the morphometric study. All of the observed alterations were present only in the gut mucosa, and intestinal morphometric study revealed no effect of inulin or B. subtilis on the intestinal absorptive area. Furthermore, experimental diets cause important alterations in the intestinal microbiota by significantly decreasing bacterial diversity, as demonstrated by the specific richness, Shannon, and range-weighted richness indices. The observed alterations demonstrate that fish fed experimental diets had different signs of gut oedema and inflammation that could compromise their body homeostasis, which is mainly maintained by the epithelial lining of the gastrointestinal tract. To our knowledge, this is the first in vivo study regarding the implications of the use of synbiotics (conjunction of probiotics and prebiotics) on fish gut morphology and microbiota.

Acute aerocystitis in Piaractus mesopotamicus: participation of eicosanoids and pro-inflammatory cytokines

A total of 360 pacus (Piaractus mesopotamicus) were used to study vascular permeability (VP) and inflammatory cell component (CC) in induced aerocystitis in P. mesopotamicus through inoculation of inactivated Aeromonas hydrophila, and the effect of steroidal and nonsteroidal anti-inflammatory drugs. It was observed that after inoculation of A. hydrophila, the maximum VP occurred 180 min post-stimulus (MPS). Pretreatment with anti-inflammatory drugs inhibited VP, and the inhibitory effect of dexamethasone was seen earlier than the effects caused by meloxicam and indomethacin. Inoculation of the bacterium caused a gradual increase in the accumulation of cells, which reached a maximum 24 h post-stimulus (HPS). Pretreatment with dexamethasone, indomethacin and meloxicam reduced the accumulation of lymphocytes, thrombocytes, granulocytes and macrophages. There was no significant difference between the different doses of the drugs tested. The results suggest that eicosanoids and pro-inflammatory cytokines participate in chemical mediation in acute inflammation in pacus.

Aeromonas spp. whole genomes and virulence factors implicated in fish disease

It is widely recognized that Aeromonas infections produce septicaemia, and ulcerative and haemorrhagic diseases in fish, causing significant mortality in both wild and farmed freshwater and marine fish species that damage the economics of the aquaculture sector. The descriptions of the complete genomes of Aeromonas species have allowed the identification of an important number of virulence genes that affect the pathogenic potential of these bacteria. This review will focus on the most relevant information derived from the available Aeromonas genomes in relation to virulence and on the diverse virulence factors that actively participate in host adherence, colonization and infection, including structural components, extracellular factors, secretion systems, iron acquisition and quorum sensing mechanisms.

A combined strategy involving Sanger and 454 pyrosequencing increases genomic resources to aid in the management of reproduction, disease control and genetic selection in the turbot (Scophthalmus maximus)

Background

Genomic resources for plant and animal species that are under exploitation primarily for human consumption are increasingly important, among other things, for understanding physiological processes and for establishing adequate genetic selection programs. Current available techniques for high-throughput sequencing have been implemented in a number of species, including fish, to obtain a proper description of the transcriptome. The objective of this study was to generate a comprehensive transcriptomic database in turbot, a highly priced farmed fish species in Europe, with potential expansion to other areas of the world, for which there are unsolved production bottlenecks, to understand better reproductive- and immune-related functions. This information is essential to implement marker assisted selection programs useful for the turbot industry.

Results

Expressed sequence tags were generated by Sanger sequencing of cDNA libraries from different immune-related tissues after several parasitic challenges. The resulting database (“Turbot 2 database”) was enlarged with sequences generated from a 454 sequencing run of brain-hypophysis-gonadal axis-derived RNA obtained from turbot at different development stages. The assembly of Sanger and 454 sequences generated 52,427 consensus sequences (“Turbot 3 database”), of which 23,661 were successfully annotated. A total of 1,410 sequences were confirmed to be related to reproduction and key genes involved in sex differentiation and maturation were identified for the first time in turbot (AR, AMH, SRY-related genes, CYP19A, ZPGs, STAR FSHR, etc.). Similarly, 2,241 sequences were related to the immune system and several novel key immune genes were identified (BCL, TRAF, NCK, CD28 and TOLLIP, among others). The number of genes of many relevant reproduction- and immune-related pathways present in the database was 50–90% of the total gene count of each pathway. In addition, 1,237 microsatellites and 7,362 single nucleotide polymorphisms (SNPs) were also compiled. Further, 2,976 putative natural antisense transcripts (NATs) including microRNAs were also identified.

Conclusions

The combined sequencing strategies employed here significantly increased the turbot genomic resources available, including 34,400 novel sequences. The generated database contains a larger number of genes relevant for reproduction- and immune-associated studies, with an excellent coverage of most genes present in many relevant physiological pathways. This database also allowed the identification of many microsatellites and SNP markers that will be very useful for population and genome screening and a valuable aid in marker assisted selection programs.

Early response of gene expression in the distal intestine of Atlantic salmon (Salmo salar L.) during the development of soybean meal induced enteritis

Plant products in general and soybeans in particular can challenge the function and health of the intestinal tract. Salmonids develop an intestinal inflammation when fed diets containing soybean meal (SBM) and certain other legume ingredients. In the present study a 44K oligonucleotide salmonid microarray, qPCR and histology were used to investigate early response mechanisms in the distal intestine of Atlantic salmon (Salmo salar L.) during the first week of oral exposure to a diet containing 20% extracted SBM. The distal intestine transcriptome was profiled on days 1, 2, 3, 5 and 7 and compared to a control group fed fishmeal as the sole protein source. Histological evaluation of the distal intestine revealed the first signs of inflammation on day 5. The most prominent gene expression changes were seen on days 3 and 5. Up-regulation in immune-related genes was observed during the first 5 days, including GTPase IMAP family members, NF-kB-related genes and regulators of T cell and B cell function. Many functional genes involved in lipid metabolism, proteolysis, transport, metabolism and detoxification were initially up-regulated on days 1-3, possibly as an attempt by the tissue to compensate for the initiating immune response. Cell repair and extracellular matrix remodeling genes were up-regulated (heparanase, collagenase) on days 3 and 5. Down regulation of genes related to endocytosis, exocytosis, detoxification, transporters and metabolic processes from day 5 indicated initiation of dysfunction of digestive and metabolic functions that may occur as a result of inflammation or as a response to the introduction of soybean meal in the diet. This is the first study conducting transcriptomic profiling to characterize early responses during the development of SBMIE. Switching Atlantic salmon from a fishmeal to a 20% SBM diet resulted in rapid changes to the intestinal transcriptome, indicating an immune reaction with subsequent impaired epithelial barrier function and other vital intestinal functions.

Alteration of immune function endpoints and differential expression of estrogen receptor isoforms in leukocytes from 17β-estradiol exposed rainbow trout (Oncorhynchus mykiss)

While the endocrine system is known to modulate immune function in vertebrates, the role of 17β-estradiol (E2) in cellular immune function of teleosts is poorly understood. The cellular and molecular responses of juvenile rainbow trout (Oncorhynchus mykiss) to E2 treatment were evaluated by exposing fish to 0.47±0.02μg/L E2 (mean±SEM) for either 2 or 7d, with a subsequent 14d recovery period. After 2 and 7d of exposure to E2, hematocrit was significantly lower than in control fish. Lipopolysaccharide-induced lymphocyte proliferation was elevated on day 2 and concanavalin A-induced lymphocyte proliferation was reduced following 7d of E2 exposure. Four estrogen receptor (ER) transcripts were identified in purified trout head kidney leukocytes (HKL) and peripheral blood leukocytes (PBL). While the mRNA abundance of ERβ1 and ERβ2 was unaffected by treatment, ERα1 was up-regulated in HKL and PBL following 7d of E2 exposure. ERα2 was up-regulated in HKL after 7d of E2 exposure, but down-regulated in PBL after 2 and 7d of treatment. All parameters that were altered during the E2 exposure period returned to baseline levels following the recovery period. This study reports the presence of the full repertoire of ERs in purified HKL for the first time, and demonstrates that ERα transcript abundance in leukocytes can be regulated by waterborne E2 exposure. It also demonstrated that physiologically-relevant concentrations of E2 can modulate several immune functions in salmonids, which may have widespread implications for xenoestrogen-associated immunotoxicity in feral fish populations inhabiting contaminated aquatic environments.

An Overview of the Immunological Defenses in Fish Skin

The vertebrate immune system is comprised of numerous distinct and interdependent components. Every component has its own inherent protective value, and the final combination of them is likely to be related to an animal’s immunological history and evolutionary development. Vertebrate immune system consists of both systemic and mucosal immune compartments, but it is the mucosal immune system which protects the body from the first encounter of pathogens. According to anatomical location, the mucosa-associated lymphoid tissue, in teleost fish is subdivided into gut-, skin-, and gill-associated lymphoid tissue and most available studies focus on gut. The purpose of this paper is to summarise the current knowledge of the immunological defences present in skin mucosa as a very important part of the fish immune system, serving as an anatomical and physiological barrier against external hazards. Interest in defence mechanism of fish arises from a need to develop health management tools to support a growing finfish aquaculture industry, while at the same time addressing questions concerning origins and evolution of immunity in vertebrates. Increased knowledge of fish mucosal immune system will facilitate the development of novel vaccination strategies in fish.

The molecular cloning and characteristics of a fibrinogen-related protein (TfFREP1) gene from roughskin sculpin (Trachidermus fasciatus)

Fibrinogen-related proteins are a family of glycoproteins containing fibrinogen-like domains. Many members of these proteins play important roles in innate immune responses. We isolated a fibrinogen-related protein gene (TfFREP1) from roughskin sculpin (Trachidermus fasciatus). The TfFREP1 encoded a protein of 264 amino acids, including 231 amino acids with fibrinogen-like domains. Both quantitative real-time polymerase chain reaction and western blot analysis showed that TfFREP1 was mainly expressed in skin and gill tissues of T. fasciatus. The expression level of TfFREP1 was upregulated at both mRNA and protein levels after stimulation of lipopolysaccharide. These results suggest that TfFREP1 may be involved in T. fasciatus immune reaction.

Fish cell cultures as in vitro models of pro-inflammatory responses elicited by immunostimulants

We have tested the elicitation of innate defence-related responses in two stromal cell lines derived from the spleen (trout splenic stroma, TSS) and the pronephros (trout pronephric stroma-2, TPS-2) of rainbow trout (Oncorhynchus mykiss) after they were exposed to different concentrations of lipopolysaccharide (LPS), levamisole, or polyinosinic polycytidylic acid (poly-I:C). For comparison, cultures of rainbow trout head kidney macrophages were also included in the study, and the effect of the immunostimulants on the phagocytic activity, the intracellular and extracellular reactive oxygen species and nitric oxide production were assayed. Although the responses varied depending upon the concentration of the immunostimulants and the particular cell line, our results demonstrate that those activities were enhanced in the TSS and TPS-2 cell lines after exposure to any of the immunostimulants. These results indicate that the stromal cells of the main lympho-haemopoietic organs of O. mykiss develop innate defence responses, which are enhanced by well-known immunostimulants. In addition, such enhancement of the defence responses in the TSS and TPS-2 cell lines could be also elicited when they were exposed to conditioned supernatants from levamisole- or poly I:C-stimulated HK macrophage cultures, thus demonstrating that the haemopoietic stromal cells respond to macrophage-derived factors. Moreover, we demonstrate that the stromal cell lines constitutively expressed the Toll-like receptors TLR3, TLR5 and TLR9 genes. The results are discussed considering the role of the lympho-haemopoietic stromal cells in the innate immune responses, and the possibility of using histiotypic cell cultures of non-leucocyte cells of the haemopoietic organs to develop in vitro methods to select new immunostimulant candidates for aquaculture.

Effects of dietary Bacillus subtilis, Tetraselmis chuii, and Phaeodactylum tricornutum, singularly or in combination, on the immune response and disease resistance of sea bream (Sparus aurata L.)

Combined or individual effects of two microalgae (Phaeodactylum tricornutum and Tetraselmis chuii) and Bacillus subtilis on immune response, gene expression, and survival to challenge with Photobacterium damselae subsp. piscicida of gilthead sea bream were investigated. To test the capacity of B. subtilis to grow employing the microalgae polysaccharides as energy and carbon source, an in vitro assay was defined, and demonstrated that the digestion product of microalgae, mainly P. tricornutum, supported the growth of B. subtilis much better than glucose. For the in vivo study, fish were distributed in six equal groups (each of two replicates) and received one of the following experimental diets: C) control, non-supplemented diet; T) T. chuii 100 g kg(-1); P) P. tricornutum 100 g kg(-1); B) B. subtilis (10(7) cfu g(-1)); BT) B. subtilis (10(7) cfu g(-1))+T. chuii (100 g kg(-1)); and BP) B. subtilis (10(7) cfu g(-1))+P. tricornutum (100 g kg(-1)). The complement activity, serum IgM level, respiratory burst, phagocytic activity, and expression of seven selected immune-related genes in head-kidney were evaluated following two and four weeks of treatment. At the end of the feeding trial, fish were challenged by intraperitoneal injection of LD(50) concentration of P. damselae subsp. piscicida and mortality was recorded. This is the first study testing the immunomodulatory capacity of the microalgae used in the present work. The dietary applications of B. subtilis, T. chuii, and P. tricornutum, singly or in combination, may exhibit up-regulating effects on gilthead sea bream immune parameters. P. tricornutum demonstrated the highest immunostimulant activity. There were no significant differences between combination feeding and feeding ingredients separately. Our results demonstrated the potential of microalgae as immunostimulants for fish, although further studies regarding the implications and effects of a stimulated immune system against pathogens, especially the protective capacity against specific diseases, are necessary.

Evolution of the immune system in the lower vertebrates

The evolutionary emergence of vertebrates was accompanied by the invention of adaptive immunity. This is characterized by extraordinarily diverse repertoires of somatically assembled antigen receptors and the facility of antigen-specific memory, leading to more rapid and efficient secondary immune responses. Adaptive immunity emerged twice during early vertebrate evolution, once in the lineage leading to jawless fishes (such as lamprey and hagfish) and, independently, in the lineage leading to jawed vertebrates (comprising the overwhelming majority of extant vertebrates, from cartilaginous fishes to mammals). Recent findings on the immune systems of jawless and jawed fishes (here referred to as lower vertebrates) impact on the identification of general principles governing the structure and function of adaptive immunity and its coevolution with innate defenses. The discovery of conserved features of adaptive immunity will guide attempts to generate synthetic immunological functionalities and thus provide new avenues for intervening with faulty immune functions in humans.

Increases in immune parameters by inulin and Bacillus subtilis dietary administration to gilthead seabream (Sparus aurata L.) did not correlate with disease resistance to Photobacterium damselae

The present work evaluates the effects of inulin and Bacillus subtilis, single or combined, on immune parameters, immune-related gene expression and protection against Photobacterium damselae subsp. piscicida in gilthead seabream (Sparus aurata). Three trials were conducted. In the first trial, different concentrations of inulin (10, 15 and 30 g kg(-1)) (as a prebiotic) were administered to determine the optimal concentration for stimulating the seabream's immune system. In the second trial, the optimum concentration of inulin (10 g kg(-1)) was combined with B. subtilis (as a probiotic). Following two and four weeks of the treatment, the main immune parameters, as well as the expression of seven immune-related genes, were measured. In the final trial, fish fed the same diet as in the second trial were challenged intraperitoneally with P. damselae subsp. piscicida (10(9) cfu g(-1)). Treatment groups for the second and third trial were control (non-supplemented diet), inulin (10 g kg(-1)), B. subtilis (10(7) cfu g(-1)) and inulin + B. subtilis (10 g kg(-1) and 10(7) cfu g(-1) respectively). Dietary administration of inulin or B. subtilis for two weeks stimulated the serum complement activity and the IgM level, as well as leucocyte phagocytic activity; furthermore, inulin stimulated leucocyte respiratory burst activity. When inulin and B. subtilis were administered together (as a synbiotic), only the serum complement activity and the IgM level increased in a statistically significant manner. Furthermore, the complement activity showed a significant increase in fish fed the three experimental diets for four weeks. The challenge experiment showed that the fish fed inulin or the synbiotic diet had non-significantly lower or significantly higher cumulative mortality, respectively, compared with the control group (non-supplemented diet). These results suggest that inulin and B. subtilis modulate the immune response of the gilthead seabream, although the combined administration increases susceptibility to infection by P. damselae subsp. piscicida.

Hilyses®, fermented Saccharomyces cerevisiae, enhances the growth performance and skin non-specific immune parameters in rainbow trout (Oncorhynchus mykiss)

Effects of Hilyses(®), fermented Saccharomyces cerevisiae (S. cerevisiae), on growth, body composition and skin mucus immune components in rainbow trout were quantified. Ninety rainbow trout (105 ± 5 g) were randomly assigned to 2 groups in triplicates and fed dietary Hilyses(®) (5 g kg(-1)) or control diet without Hilyses(®) for 50 days. Results of this study demonstrated that growth performance increased significantly by the dietary yeast supplement; however body composition was not affected in treatment group. At the 45th and 50th day of feeding trial, results of mucus samples demonstrated that yeast supplementation in treatment group significantly promoted enzyme activities, namely lysozyme, protease, alkaline phosphatase and esterase compared to control group. Significant increases were also observed in hemagglutination and antibacterial activity against Yersinia ruckeri in fish fed treatment diet. The present study suggests that fermented S. cerevisiae may effectively promote the growth performance and skin non-specific immune parameters in rainbow trout.