Association of ectoparasite Lepeophtheirus salmonis counts on farmed Atlantic salmon and wild sea trout in Scotland.

Parasitic sea lice (Copepoda: Caligidae) colonising marine salmonid (Salmoniformes: Salmonidae) aquaculture production facilities have been implicated as a possible pressure on wild salmon and sea trout populations. This investigation uses monitoring data from the mainland west coast and Western Isles of Scotland to estimate the association of the abundance of adult female Lepeophtheirus salmonis (Krøyer) colonising farmed Atlantic salmon Salmo salar L. with the occurrence of juvenile and mobile L. salmonis on wild sea trout, anadromous S. trutta L. The associations were evaluated using generalised linear mixed models incorporating farmed adult female salmon louse abundances which are temporally lagged relative to dependent wild trout values. The pattern of lags, which is consistent with time for L. salmonis development between egg and infective stage, was evaluated using model deviances. A significant positive association is identified between adult female L. salmonis abundance on farms and juvenile L. salmonis on wild trout. This association is consistent with a causal relationship in which increases in the number of L. salmonis copepodids originating from lice colonising farmed Atlantic salmon cause an increase of L. salmonis abundance on wild sea trout.

Determination of Raman spectrum under different culture conditions: preliminary research on bacterial fish pathogens.

The intensive labour and time required for conventional methods to identify bacterial fish pathogens have revealed the need to develop alternative methods. Raman spectroscopy has been used in the rapid optical identification of bacterial pathogens in recent years as an alternative method in microbiology. Strains of bacterial fish pathogens (Vibrio anguillarum, Lactococcus garvieae and Yersinia ruckeri) that often cause infectious diseases in fish were here identified and analyzed in terms of their biochemical structures in different media and at different incubation times, and the data were specified by using Raman spectroscopy. The results demonstrated that Raman spectroscopy presents species-specific Raman spectra of each disease-causing bacteria and that it would be more appropriate to choose general microbiological media over selective media for routine studies. Additionally, it was found that species-specific band regions did not differ in 24- and 48-hour cultures, but there could be a difference in peak intensity which may lead to difficult characterization of spectrum. The current study, conducted for the first time with bacterial fish pathogens under different incubation conditions, is believed to provide a basis for the routine use of Raman spectroscopy for quick pathogen identification and the precise determination of the methodology for further research.

Microbiome and network analysis reveal potential mechanisms underlying Carassius auratus diseases: The interactions between critical environmental and microbial factors.

Despite the rapid development of research on aquatic environment microbiota, limited attention has been paid to exploring the complex interactions between microbial communities and aquatic environments. Particularly, the mechanisms underlying fish diseases based on such dynamic interactions remain unknown. This study aimed to address the gap by conducting microbiome and co-occurrence network analyses on the typical freshwater aquaculture systems. High-throughput 16S rRNA gene sequencing results revealed significant differences in the microbiota between the disease and healthy groups. Notably, disease mortality varied consistently with the gradient of relative abundance of Proteobacteria (intestine, R2 = 0.46, p < 0.05) and Cyanobacteria (gill, R2 = 0.67, p < 0.01), indicating their potential use as diagnostic criteria. Furthermore, the elevated hepatosomatic index, NO3-N, COD and TC (sediment) were directly correlated with diseases (r > 0.54, p < 0.01). Mean concentrations of NO3-N, COD and TC were elevated by 78.87%, 25.63% and 44.2%, respectively, in ponds where diseases occurred. Quantitative analysis (qPCR) revealed that Aeromonas sobria infected hosts through a potential pathway of "sediment (4.4 × 105 copy number/g)-water (1.1 × 103 copy number/mL)-intestine (1.2 × 106 copy number/g)". Similarly, the potential route for Aeromonas veronii was sediment (4.9 × 106 copy number/g) to gill (5.1 × 105 copy number/g). Additionally, the complexity of microbial networks in the intestine, water, and sediment was significantly lower in the disease group, although no similar phenomenon was observed in the gill microbial network. In summary, these findings reveal that elevated concentrations of crucial environmental factors disrupt the linkages within microbiota, fostering the growth of opportunistic bacteria capable of colonizing fish gut or gills. This offers new insights into potential mechanisms by which environmental factors cause disease in fish.

First preliminary study on identification of bacterial fish pathogens with Raman spectroscopy.

Accurate and rapid determination of bacterial disease agents of fish is an important step for sustainable and efficient aquaculture production. In general, biochemical and molecular methods are used for pathogen detection but they are usually time-consuming and required qualified personnel. Recently spectroscopic methods are preferred in clinical and food microbiology and declared as a promising alternative method for pathogens diagnosis with many advantages. In this study, the significant spectra of three important bacterial fish pathogens (Lactococcus garvieae, Vibrio anguillarum and Yersinia ruckeri) were determined by Raman spectroscopy. The first data of the pathogens were obtained and the distinctive differences in polysaccharides, nucleic acids, fatty acids and amino acids were identified. This preliminary study aimed to be pioneer for further studies in aquaculture and veterinary microbiology toward developing an alternative method for routine identification.

Effect of dietary celery (Apium graveolens) on the growth performance, immune responses, and bacterial resistance against Vibrio anguillarum of European seabass (Dicentrarchus labrax).

In this study, we evaluated to reveal the effects of aqueous methanolic extract of celery (Apium graveolens) on the growth performance, immune responses, and resistance against Vibrio anguillarum in European seabass (Dicentrarchus labrax). For this purpose, twenty fish (initial mean weight of 4.80 ± 0.06 g) were placed into twelve tanks (400 L) in triplicate and fish were fed with control (C) and three different levels (0.01, 0.05, and 0.1 g/kg) of A. graveolens (AG) extract-containing diets (AG0.01, AG0.05, and AG0.1) for 30 days. Blood and tissue (kidney, spleen, and intestine) samples were taken from the fish every 10 days during the study to determine the immune responses of the fish. Respiratory burst activity (RBA) was significantly decreased in the AG0.1 group compared to all other groups on the 10th day of the study (P < 0.05). Significance was noticed in the RBA of fish in all AG groups compared to the C group (P < 0.05) on the 30th day of the experiment Lysozyme activity (LYS) was raised on the 10th day of the study in all celery groups compared to the C group (P < 0.05). No differences in the myeloperoxidase activity (MPO) were observed among the experimental groups (P > 0.05). The final mean weight (FMW) was not affected in any experimental groups (P > 0.05). However, in the AG0.05 group, the specific growth rate (SGR) increased, and the feed conversion ratio (FCR) decreased compared to other groups (P < 0.05). IL-1ß in the kidney was highly elevated in the AG0.01 group on the 20th day of the study (P < 0.05). Similar results were observed on IL-6, IL-8, and TNF-α expression in the kidney (P < 0.05). Anti-inflammatory responses (IL-10 and TGF-ß) also increased in all experimental groups and tissues compared to the C group (P < 0.05). COX-2 was upregulated on the 20th day of the study in all tissues (P < 0.05). At the end of the feeding trial, the survival rate of the AG0.1 group in fish infected with Vibrio anguillarum infection was higher than the C group. Dietary celery extract did not affect growth performance directly but increased innate immune responses and a high survival rate. Overall, compared to the control group, the growth, immunity, and resistance of European seabass fed with a diet containing 0.05 g/kg celery aqueous methanolic extract has been improved, and this could be used as an immunostimulant feed additive.

The effects of two dietary synbiotics on growth performance, haematological parameters, and non-specific immune responses in Japanese eel (Anguilla japonica).

Feed additives have attracted increased attention in aquaculture due to their ability to modulate fish gut microbiota, resulting in improved fish growth and immunity. This study assessed two synbiotics' effects in Japanese eels: Bacillus subtilis with mannooligosaccharide (MOS) and Enterococcus faecium with fructooligosaccharide (FOS). Six diets, including a control (CON), oxytetracycline (OTC), and four synbiotic diets - B.subtilis at 1 × 106 and 107 CFU/g with 5 g/kg MOS (BS6MO and BS7MO) and E. faecium at 1 × 106 and 107 CFU/g with 5 g/kg FOS (EF6FO and EF7FO) - were fed to triplicate groups of 20 fish averaging 6.00 ± 0.07g for eight weeks. Fish fed the BSMOS diets showed significantly higher weight gain (WG), specific growth rate (SGR), and feed efficiency (FE) compared to the CON and OTC diets (P < 0.05), but not significantly different from those fed the EFFOS diets. Weight gain, SGR of fish fed EFFOS were not significantly different from those fed all other diets (P > 0.05). Fish fed the OTC diet showed a higher mean aspartate aminotransferase (AST) level, though the difference was not statistically significant. The myeloperoxidase (MPO) activity of fish fed the BS7MO diet was significantly higher than in all other diets, and the superoxide dismutase (SOD) activity of fish fed the BS7MO diet was also significantly higher than in the EF7FO diet. Overall, the BSMOS synbiotic diets were significantly more effective than the CON diet in enhancing fish survival against Vibrio anguillarum. Our findings suggest that synbiotics can be a preferable alternative to antibiotics in aquaculture.

Prevalence of bacterial infections and the use of multiplex PCR assay for rapid detection of pathogens in cultured fish in Ghana.

The modern and rapid avenue for detecting pathogens provided by molecular genetic techniques including polymerase chain reaction (PCR) was explored in the present study to identify prevalent disease pathogens, from six aquaculture farms and in two commonly cultured fish in Ghana. The specific detection was carried out directly on clinical samples of naturally infected fish (O. niloticus and C. gariepinus) based on syber-mix reaction protocol in traditional PCR. Molecular diagnostic techniques allowed the detection of the six most common and important bacterial pathogens in aquaculture farms in Ghana. Also, three of the pathogens (Streptococcus agalactiae, Streptococcus iniae, and Staphylococcus aureus) were simultaneously isolated in a multiplex reaction. The results indicated 90-100% sensitivity and specificity for each of the six bacterial pathogens tested. Streptococcosis and motile aeromonad septicemia were found to be highly prevalent in most aquaculture farms in Ghana with severity in infections traced to the 85.7% and 14.9% co-infections with all six target pathogens in catfish and tilapia respectively. The prevalence rate of infections significantly correlated with variations in salinity, conductivity, and dissolved oxygen concentrations in the thermal stressed condition of the culture water. Multiplex techniques employed in this study represent one of the first to be used by a fish health laboratory in Ghana for rapid detection of pathogens in diseased fish and could be a useful alternative to the culture-based method for routine diagnosis of fish diseases in Ghana.

The effective components of herbal medicines used for prevention and control of fish diseases.

The increasing demand for fish consumption has promoted the rapid development of fish aquaculture. With the continuous expansion of culture scale and the deterioration of culture environment, various diseases have broken out frequently, leading to huge economic losses to fish farming. Antibiotics and chemicals are common options to prevent and control of fish diseases, but their use is now restricted or even banned due to serious problems such as drug residues, pathogen resistance, and environmental pollution. Herbs and their extracts have increasingly become promising supplements and alternatives, because of their effectiveness, safety, environmental friendliness and less drug resistance. The application of herbal medicines in prevention and control of fish diseases is mainly attributed to the powerful immune enhancement, antioxidation or direct anti-pathogenic efficacies of their effective components, including mainly polyphenols, polysaccharides, saponins, flavonoids, alkaloids, and essential oils. Recently these herbal active ingredients have been extensively studied for their efficacies in prevention and control of viral, bacterial, parasitic, and fungal diseases in fish. In the present paper, we comprehensively summarize the research progress of the active ingredients of herbal medicines used for prevention and control of fish diseases, especially of their action mechanisms, and highlight the potential application of the herbal medicines in fish aquaculture.

Clinico-pathological findings and expression of inflammatory cytokines, apoptosis, and oxidative stress-related genes draw mechanistic insights in Nile tilapia reared under ammonia-N exposure and Aeromonas hydrophila challenge.

Fish diseases have a "stress-related" nature, whereas fish exposure to stressors will increase their susceptibility to infections. It was also noted that fish exposure to biotic and abiotic stressors would exaggerate the disease signs, elicit high mortalities, and cause severe economic losses. Motile aeromonad septicemia (MAS) is a major bacterial disease affecting a variety of finfish species throughout the globe and is caused by Aeromonas hydrophila. Herein, we have evaluated the impacts of ammonia-N stress and/or Nile tilapia challenge with pathogenic A. hydrophila on the clinical picture of MAS disease. Clinical signs, postmortem lesions, histoarchitectural changes, and gene transcription analysis were studied. Fish experimentally infected with A. hydrophila were exophthalmic and showed darkened skin. Moreover, opercular hyperemia, petechial hemorrhages, and gill congestion alongside dermal ulcerations were noticed in ammonia-exposed fish. On the other side, fish exposed to both stressors exhibited exophthalmia, corneal opacity, severe dropsy, and hemorrhagic dermal ulcerations. At the tissue levels, the histopathological lesions were exaggerated in the fish group exposed to ammonia stress and challenged with A. hydrophila than fish group exposed to each one alone. At the molecular levels, the mRNA expression analysis reveals significant upregulation of inflammatory cytokines such as interleukin-1 beta, CXC chemokine, and tumor necrosis factor-alpha in the kidney tissues of Nile tilapia exposed to ammonia and/or challenged with A. hydrophila. In a similar trend, the mRNA expression values of heat shock protein 70 (HSP70), oxidative stress related genes (SOD and CAT) and apoptosis-related genes (caspase 3, BAX, and cytochrome P450) were also increased in the hepatic tissues of fish exposed to singular or dual stressors. Interestingly, the highest expression levels of the above-mentioned genes were found in the fish group exposed to both stressors. Taken together, these findings indicate the occurrence of severe inflammatory and apoptotic changes in fish exposed to ammonia and infected with A. hydrophila more than each one alone. In contrast, there was a significant decrease in the expression values of the antioxidant enzyme glutathione-S-transferase (GST) in stressed fish, suggesting the occurrence of oxidative stress. This study will be helpful to draw mechanistic insights into the exposure of fish to ammonia stress and infection with A. hydrophila.

In vitro modulation of gilthead seabream (Sparus aurata L.) leukocytes by Bacillus spp. extracellular molecules upon bacterial challenge.

Stimulation of the fish immune system using immunostimulants is an environmentally friendly strategy to minimize bacterial outbreaks in aquaculture. Different biological and synthetic immunostimulants can enhance non-specific innate immune responses by directly activating immune cells. An example are Bacillus spp., known for their immunostimulatory effects, although the exact mechanisms by which Bacillus spp. offer protection against diseases remains to be elucidated. Furthermore, most studies have focused on Bacillus spp. cells, while the immunostimulant effect of their extracellular metabolome, known to harbour biologically important metabolites, including antimicrobial molecules, has been scarcely evaluated. Here, we evaluated the in vitro immune-modulatory properties of extracellular extracts of three Bacillus spp. strains (B. subtilis FI314, B. vezelensis FI436 and B. pumilus FI464), previously isolated from fish-guts and characterized for their in vitro and in vivo antimicrobial activity against a wide range of fish pathogens. Bacillus spp. extracellular extracts did not affect immune cells viability, but remarkably increased pathogens' phagocytosis when seabream head-kidney leukocytes were challenged with Vibrio anguillarum and Edwardsiella tarda. All extracts significantly increased the engulfment of bacterial pathogens 1 h post-infection. Cells stimulated with the extracellular extracts showed an up-regulation of the expression of immune-relevant genes associated with inflammation, including IL-1ß, IL-6, and COX-2. In cells challenged with E. tarda, FI314 extracellular extract significantly increased the expression of IL-1ß, IL-6, and COX-2, while FI436 and FI464 significantly increased IL-6 expression. The results of this study revealed that the extracellular molecules from Bacillus spp. fish isolates improved the in vitro response of gilthead seabream immune cells and are thus promising candidates to act as immunostimulants, helping fish fight diseases.

Therapeutic Intervention with Dietary Chitosan Nanoparticles Alleviates Fish Pathological and Molecular Systemic Inflammatory Responses against Infections.

Marine bio-sourced chitosan nanoparticles (CSNP) are antimicrobial and immunomodulatory agents beneficial for fish medicine. Herein, dietary CSNP was investigated for the amelioration of the systemic inflammatory responses of an induced fish model. One hundred and forty-four rainbow trout were assigned to one pathogen-free and non-supplemented group (negative control), and three challenged groups: non-supplemented (positive control), CSNP-preventive, and CSNP-therapeutic. After a feeding experiment extended for 21 days, the organosomatic indices (OSI) and molecular aspects were assessed. After a challenge experiment extended for further 28 days, CSNP-therapeutic intervention was assessed on fish survival and systemic inflammatory responses on pathology, histo-morphology, and molecular aspects. With CSNP administration, OSI nonsignificantly decreased and the relative expression of targeted inflammatory-mediator genes was significantly increased. The CSNP-therapeutic fish showed an RPS of 80% as compared to the positive control group, and CSNP-therapeutic administration retained the highest gene expression augmentation up to 28 days after the challenge. Notably, the splenic reticulin fibers framework of the CSNP-therapeutic group retained the highest integrity among the groups during the infection. After recovery, reticulin fibers density in the CSNP-therapeutic samples was significantly higher than in the negative control group, which indicates high innate immunity. Thus, CSNP showed promising biotherapeutic features enhancing fish resistance against infections.

Identification of Key Functions Required for Production and Utilization of the Siderophore Piscibactin Encoded by the High-Pathogenicity Island irp-HPI in Vibrionaceae.

Piscibactin is a widespread siderophore system present in many different bacteria, especially within the Vibrionaceae family. Previous works showed that most functions required for biosynthesis and transport of this siderophore are encoded by the high-pathogenicity island irp-HPI. In the present work, using Vibrio anguillarum as a model, we could identify additional key functions encoded by irp-HPI that are necessary for piscibactin production and transport and that have remained unknown. Allelic exchange mutagenesis, combined with cross-feeding bioassays and LC-MS analysis, were used to demonstrate that Irp4 protein is an essential component for piscibactin synthesis since it is the thioesterase required for nascent piscibactin be released from the NRPS Irp1. We also show that Irp8 is a MFS-type protein essential for piscibactin secretion. In addition, after passage through the outer membrane transporter FrpA, the completion of ferri-piscibactin internalization through the inner membrane would be achieved by the ABC-type transporter FrpBC. The expression of this transporter is coordinated with the expression of FrpA and with the genes encoding biosynthetic functions. Since piscibactin is a major virulence factor of some pathogenic vibrios, the elements of biosynthesis and transport described here could be additional interesting targets for the design of novel antimicrobials against these bacterial pathogens.

Bacillus spp. Inhibit Edwardsiella tarda Quorum-Sensing and Fish Infection.

The disruption of pathogen communication or quorum-sensing (QS) via quorum-quenching (QQ) molecules has been proposed as a promising strategy to fight bacterial infections. Bacillus spp. have recognizable biotechnology applications, namely as probiotic health-promoting agents or as a source of natural antimicrobial molecules, including QQ molecules. This study characterized the QQ potential of 200 Bacillus spp., isolated from the gut of different aquaculture fish species, to suppress fish pathogens QS. Approximately 12% of the tested Bacillus spp. fish isolates (FI). were able to interfere with synthetic QS molecules. Ten isolates were further selected as producers of extracellular QQ-molecules and their QQ capacity was evaluated against the QS of important aquaculture bacterial pathogens, namely Aeromonas spp., Vibrio spp., Photobacterium damselae, Edwardsiela tarda, and Shigella sonnei. The results revealed that A. veronii and E. tarda produce QS molecules that are detectable by the Chr. violaceum biosensor, and which were degraded when exposed to the extracellular extracts of three FI isolates. Moreover, the same isolates, identified as B. subtilis, B. vezelensis, and B. pumilus, significantly reduced the pathogenicity of E. tarda in zebrafish larvae, increasing its survival by 50%. Taken together, these results identified three Bacillus spp. capable of extracellularly quenching aquaculture pathogen communication, and thus become a promising source of bioactive molecules for use in the biocontrol of aquaculture bacterial diseases.

A commercial autogenous injection vaccine protects ballan wrasse (Labrus bergylta, Ascanius) against Aeromonas salmonicida vapA type V.

Atypical Aeromonas salmonicida (aAs) and Vibrionaceae related species are bacteria routinely recovered from diseased ballan wrasse used as cleaner fish in the Atlantic salmon farming industry. Autogenous (i.e. farm specific inactivated) multivalent vaccines formulated from these microorganisms are widely used to protect farmed wrasse despite limited experimental proof that they are primary pathogens. In this study, the components of a commercial multivalent injection vaccine containing four strains of Aeromonas salmonicida and one strain of Vibrio splendidus previously isolated from ballan wrasse in Scotland, were tested for infectivity, pathogenicity and virulence via intra peritoneal injection at pre-deployment size (25-50 g) and the efficacy of the vaccine for protection against aAs assessed. Injection with 3.5 × 109, 8 × 109 1.8 × 109 and 5 × 109 cfu/fish of Vibrio splendidus, V. ichthyoenteri, Aliivibrio logeii and A. salmonicida, respectively, did not cause significant mortalities, lesions or clinical signs after a period of 14 days. IP injection with both aAs and Photobacterium indicum successfully reproduced the clinical signs and internal lesions observed during natural outbreaks of the disease. Differences in virulence (LD50 at day 8-post infection of 3.6 × 106 cfu/fish and 1.6 × 107 cfu/fish) were observed for two aAs vapA type V isolates. In addition, the LD50 for Photobacterium indicum was 2.2 × 107 cfu/fish. The autogenous vaccine was highly protective against the two aAs vapA type V isolates after 700-degree days of immunisation. The RPSFINAL values for the first isolate were 95 and 91% at 1 × 106 cfu/fish and 1 × 107 cfu/fish, respectively, and 79% at 1 × 107 cfu/fish for the second isolate tested. In addition, significantly higher anti aAs seral antibodies (IgM), were detected by ELISA in vaccinated fish in contrast with control (mock vaccinated) fish. These results suggest wrasse can be effectively immunised and protected against aAs infection by injection with oil adjuvanted vaccines prepared with inactivated homologous isolates.

Efficacy of silver nanoparticles to control flavobacteriosis caused by Flavobacterium johnsoniae in common carp Cyprinus carpio.

Flavobacterial infections are among the causes of fish losses in farms with the emergence of antibiotic-resistant isolates. Silver nanoparticles (AgNPs) are known for their potent antimicrobial activity against different types of bacteria. In this study, we evaluated the antibacterial properties of AgNPs (diameter: 23 nm) against Flavobacterium johnsoniae infection in common carp Cyprinus carpio. The assays included both in vitro and in vivo antibacterial tests in addition to evaluation of cell toxicity effects on the fish cell lines. The in vitro results revealed potent inhibitory effects of AgNPs on the growth of F. johnsoniae with a minimum inhibitory concentration of 34 µg ml-1. Fish cell (epithelioma papulosum cyprini and koi carp fin) viability was 95-100% after exposure to 500 ng ml-1 (and lower concentrations) of AgNPs. In the exposure experiment, mortality rates decreased from 45% in the infected non-treated group to 30 and 15% in the intraperitoneal injection and immersion-treated groups, respectively. Neither of the treated groups showed any clinical signs or histopathological lesions. The single-dose treatment with AgNPs during early infection with F. johnsoniae aided in minimizing fish losses.

Experimental transmission of Caligus rogercresseyi between two different fish species.

Caligus rogercresseyi is the dominant sea louse parasite affecting the salmon and trout industry in southern Chile. This parasite has a wide range of native and endemic fish hosts. The Patagonian blenny Eleginops maclovinus, which is parasitized mostly by the caligid species Lepeophtheirus spp. and C. rogercresseyi, is presumably responsible for the transmission of C. rogercresseyi to salmonids. The aim of this study was to characterize the transmission of parasites between different fish species and parasite cohort development under laboratory conditions. Parasite abundances and intensities were quantified. Transmission of parasites from Patagonian blenny to Atlantic salmon Salmo salar was lower (~9%, mainly corresponding to C. rogercresseyi) than from salmon to Patagonian blenny (14.7-26.9%, where only C. rogercresseyi were observed). This suggests that the transmission of C. rogercresseyi from salmon individuals is higher than the transmission from a native fish. Parasite cohorts developed successfully on both fish species, but apparently under different developmental rates. Water temperature, oxygen, and juvenile abundances were the variables that better explained cohort development success and variation in C. rogercresseyi adult abundances over time.

Review of diseases and health management in zebrafish Danio rerio (Hamilton 1822) in research facilities.

The use of zebrafish (Danio rerio) in biomedical research has expanded at a tremendous rate over the last two decades. Along with increases in laboratories using this model, we are discovering new and important diseases. We review here the important pathogens and diseases based on some 20 years of research and findings from our diagnostic service at the NIH-funded Zebrafish International Resource Center. Descriptions of the present status of biosecurity programmes and diagnostic and treatment approaches are included. The most common and important diseases and pathogens are two parasites, Pseudoloma neurophilia and Pseudocapillaria tomentosa, and mycobacteriosis caused by Mycobacterium chelonae, M. marinum and M. haemophilum. Less common but deadly diseases are caused by Edwardsiella ictaluri and infectious spleen and kidney necrosis virus (ISKNV). Hepatic megalocytosis and egg-associated inflammation and fibroplasia are common, apparently non-infectious, in zebrafish laboratories. Water quality diseases include supersaturation and nephrocalcinosis. Common neoplasms are spindle cell sarcomas, ultimobranchial tumours, spermatocytic seminomas and a small-cell carcinoma that is caused by a transmissible agent. Despite the clear biosecurity risk, researchers continue to use fish from pet stores, and here, we document two novel coccidia associated with significant lesions in zebrafish from one of these stores.

Current status of fish vaccines in Japan.

Aquaculture is an important industry in Japan for the sustainable production of fish. It contributes to the diversity of Japanese traditional food culture, which uses fish such as "sushi" and "sashimi". In the recent aquaculture setting in Japan, infectious diseases have been an unavoidable problem and have caused serious economic losses. Therefore, there is an urgent need to overcome the disease problem to increase the productivity of aquaculture. Although our country has developed various effective vaccines against fish pathogens, which have contributed to disease prevention on fish farms, infectious diseases that cannot be controlled by conventional inactivated vaccines are still a problem. Therefore, other approaches to developing effective vaccines other than inactivated vaccines are required. This review introduces the vaccine used in Japan within the context of the current status of finfish aquacultural production and disease problems. This review also summarizes the current research into vaccine development and discusses the future perspectives of fish vaccines, focusing on the problems associated with vaccine promotion in Japan.

Effect of catecholamine stress hormones (dopamine and norepinephrine) on growth, swimming motility, biofilm formation and virulence factors of Yersinia ruckeri in vitro and an in vivo evaluation in rainbow trout.

In this study, we evaluated the impact of the catecholamines on growth, swimming motility, biofilm formation and some virulence factors activities of pathogenic Yersinia ruckeri. Norepinephrine and dopamine (at 100 µM) significantly increased the growth of Y. ruckeri in culture media containing serum. An increase in swimming motility of the pathogen was found following the exposure to the hormones; however, no effect was seen on caseinase, phospholipase and haemolysin productions. Further, antagonists for the catecholamine receptors were observed to block some of the influences of the catecholamines. Indeed, the effects of catecholamines were inhibited by chlorpromazine (the dopaminergic receptor antagonist) for dopamine, labetalol (α-and ß-adrenergic receptor antagonist) and phenoxybenzamine (the α-adrenergic receptor antagonist) for norepinephrine, but propranolol (the ß-adrenergic receptor antagonist) showed no effect. Pretreatment of Y. ruckeri with the catecholamines resulted in a significant enhancement of its virulence towards rainbow trout and the antagonists could neutralize the effect of the stress hormones in vivo. In summary, our results show that the catecholamines increase the virulence of Y. ruckeri which is pathogenic to trout through increasing the motility, biofilm formation and growth.

Morphological and molecular characterization of Myxobolus dibombensis sp. n. (Myxozoa: Myxobolidae), a parasite of the African carp Labeobarbus batesii (Teleostei: Cyprinidae) from Dibombe River, Cameroon.

Myxobolus dibombensis sp. n. (Cnidaria: Myxosporea: Bivalvulida) is described from the fins of the African carp, Labeobarbus batesii, based on morphological and molecular data. Prevalence of infection was 51.9% (67/129). Ovoid to spherical cyst-like plasmodia were found in the intrasegmental region and among the fin rays. No pathological changes were found in the fish host tissue surrounding the cyst-like plasmodia. Mature myxospores were ovoid in frontal view and lenticular in lateral view, with slightly truncated anterior and rounded posterior ends. Myxospores measured 16.8 (15.8-18.0) µm long and 11.4 (10.0-13.0) µm wide. There was a triangular intercapsular appendix measuring 3.8 (2.6-4.5) µm long. Polar capsules were ovoid and slightly unequal in size, occupying approximately one-third of the myxospore length. The larger polar capsule measured 7 (6-8) µm long and 3.6 (3-4) µm wide, while the smaller one measured 5.8 (4.8-7.0) µm long and 3 (2-4) µm wide. The larger polar capsule contained nine to 11 filament coils, whereas the smaller one contained seven to nine coils. SSU rDNA gene sequence of M. dibombensis sp. n. did not match any sequences available in the GenBank. The similarity with available Myxobolus spp. sequences ranged from 65 to 81%. The novel species clustered with M. algonquinensis, which infects the cyprinid Luxilus cornutus from Canada.