Journal of fish diseases最新文献

Pacific pink salmon (Oncorhynchus gorbuscha) were deliberately introduced to rivers surrounding the White Sea and has spread to Norway and several other countries surrounding the North Atlantic Ocean. In August 2021, a female pink salmon displaying pale gills and abnormal behaviour was captured in River Lakselva in Northern Norway and later submitted to the Norwegian Veterinary Institute (NVI) for post-mortem examination. Histological examination of organ samples revealed structures indicative of systemic ichthyophoniasis, caused by Ichthyophonus sp. The parasites appeared to be especially abundant in the heart and skeletal musculature, and local tissue responses were assessed to be absent or very mild. Sequences of the ribosomal 18S rRNA and the mitochondrial cytochrome oxidase 1 (CO1) genes confirmed the diagnosis and identified the pathogen as Ichthyophonus sp. The CO1 sequence further established that the isolate from pink salmon was most similar to sequences of Ichthyophonus sp. from Atlantic salmon, Salmo salar, from the Atlantic Ocean on the east coast of the US and from Atlantic herring, Clupea harengus, from Iceland. We here report the first detection of Ichthyophonus sp. in pink salmon in the North Atlantic Ocean.

Fish meal (FM) replacement is essential for the sustainable expansion of aquaculture. This study focussed on the feasibility of replacing FM with a single-cell protein (SCP) derived from methanotrophic bacteria (Methylococcus capsulatus, Bath) in barramundi fry (Lates calcarifer). Three isonitrogenous and isoenergetic diets were formulated with 0%, 6.4% and 12.9% inclusion of the SCP, replacing FM by 0%, 25% and 50%. Barramundi fry (initial body weight 2.5 ± 0.1 g) were fed experimental diets for 21 days to assess growth performance, gut microbiome composition and gut histopathology. Our findings revealed that both levels of SCP inclusion induced detrimental effects in barramundi fry, including impaired growth and reduced survival compared with the control group (66.7% and 71.7% survival in diets replacing FM with SCP by 25% and 50%, respectively; p < .05). Both dietary treatments presented mild necrotizing enteritis with subepithelial oedema and accumulation of PAS positive, diastase resistant droplets within hepatocytes (ceroid hepatopathy) and pancreatic atrophy. Microbiome analysis revealed a marked shift in the gut microbial community with the expansion of potential opportunistic bacteria in the genus Aeromonas. Reduced overall performance in the highest inclusion level (50% SCP) was primarily associated with reduced feed intake, likely related to palatability issues, albeit pathological changes observed in gut and liver may also play a role. Our study highlights the importance of meticulous optimization of SCP inclusion levels in aquafeed formulations, and the need for species and life-stage specific assessments to ensure the health and welfare of fish in sustainable aquaculture practices.

Edwardsiella anguillarum, a highly virulent species within the Edwardsiella genus, causes significant mortality in milkfish farms in Taiwan. This study aimed to investigate the comparison of milkfish susceptibility, a newly identified host species in Taiwanese aquaculture, with other species Nile tilapia (Oreochromis niloticus) and Asian seabass (Lates calcarifer), to E. anguillarum, elucidating its pathogenicity across both seawater and freshwater aquaculture environments. The results showed milkfish exhibited the highest mortality rate of 85% within 48 h of infection, whereas Nile tilapia exhibited a mortality rate of 70% between the second- and tenth-day post challenge, and seabass exhibited a mortality rate of 25% between the second- and sixth-day post challenge. Gross lesions observed in milkfish included splenomegaly and haemorrhage, whereas Nile tilapia exhibited signs of ascites, exophthalmia and brain haemorrhage. Seabass displayed spleen granulomas and haemorrhage at the injection site. Histopathological analysis revealed common features across all three species, including multifocal necrosis, bacterial presence in the necrotic areas, serositis and oedema. Asian seabass also exhibited chronic lesions in the form of splenic granulomas. This study highlights the high susceptibility of milkfish and Nile tilapia to E. anguillarum, emphasizing the urgent need for further investigation into targeted vaccine development for these fish species. These results not only deepen our understanding of the differing levels of pathogenicity among the three species but also offer valuable insights for improving disease prevention and management strategies in aquaculture, including those applied within polyculture systems and for the maintenance of aquaculture water environments.

Aeromonas veronii is an important pathogen found in various aquatic environments and products, posing a threat to public health. The Hanks-like serine/threonine protein kinase is closely linked to the pathogenesis of pathogenic bacteria, but the exact role of YihE in A. veronii remains still unknown. To study the specific function of the YihE kinase, we constructed a knockout mutant of the yihE gene in A. veronii. The deletion of the yihE gene resulted in changes to the metabolism of L-arginine-AMC and acetic acid, as well as enhanced resistance to ampicillin and kanamycin in A. veronii. Additionally, the ΔyihE strain demonstrated a 1.4-fold increase in biofilm formation ability and a 1.8-fold decrease in adhesion and invasion to EPCs when compared to the wild-type strain. A significant decrease in cytotoxicity was observed at 2 and 3 h post-infection with EPCs compared to the wild-type strain. Additionally, the deletion of the yihE gene was associated with a significant decrease in motility of the strain. Furthermore, the deletion of the yihE gene resulted in a 1.44-fold increase in the LD₅₀ of A. veronii in zebrafish. These findings offer valuable insights into the pathogenic mechanisms of A. veronii.

The increasing significance of the aquaculture sector and commercially valuable species underscores the need to develop alternatives for controlling diseases such as Ichthyophthirius multifiliis-induced ichthyophthiriasis. This ciliated protozoan parasite threatens nearly all freshwater fish species, causing substantial losses in the fishery industry. Despite this, effective large-scale treatments are lacking, emphasizing the necessity of adopting preventive strategies. While the pathogenesis of ichthyophthiriasis and its immune stimulation allows for vaccination strategies, precise adjustments are crucial to ensure the production of an effective vaccine compound. Therefore, this study aimed to evaluate the impact of immunizing Astyanax lacustris with a genetic vaccine containing IAG52A from I. multifiliis and the molecular adjuvant IL-8 from A. lacustris. Transcript analysis in immunized A. lacustris indicated mRNA production in fish muscles, demonstrating an expression of this mRNA. Fish were divided into five groups, receiving different vaccine formulations, and all groups received a booster dose 14 days after the initial immunization. Samples from vaccinated fish showed increased IL-1β mRNA expression in the spleen within 6 h post the second dose and after 14 days. In the head kidney, IL-1β mRNA expression showed no significant difference at 6 and 24 h but an increase was noted in fish injected with IAG and IAG + IL-8 after 14 days. IL-8 mRNA expression in the spleen and kidney did not significantly differ from the control group. Histological analysis revealed no variation in leukocyte concentration at 6 and 24 h post-vaccination; however, after 14 days, the groups injected with IAG and IAG + IL-8 exhibited a higher leukocyte density at the application sites than the control. The obtained data suggest that the used vaccine is transcribed, indicating its potential to stimulate innate immune response parameters through mRNA cytokine expression and leukocyte migration.

The introduced salmonid ectoparasite Gyrodactylus salaris has been detected on Atlantic salmon in 53 Norwegian rivers and in 39 Norwegian fish farms. In affected rivers, the mortality of Atlantic salmon juveniles is very high, estimated to a mean of 86%. G. salaris has been considered one of the biggest threats to wild Norwegian Atlantic salmon stocks. With various measures, the authorities have reduced the potential for further spread of the parasite to new rivers and fish farms, and G. salaris has been eradicated from 43 rivers and all fish farms. Furthermore, the eradication process is almost completed in five affected rivers located at the Norwegian west coast, while preparations for the eradication in the remaining five rivers in the southeastern part of Norway have begun. The goal of Norwegian management is to eradicate the introduced pathogenic G. salaris strains from all occurrences in Norway. In fish farms, the parasite has been removed by mandatory slaughter of infected fish. In rivers, G. salaris has mostly been removed by killing all the fish hosts with rotenone. The indigenous genetic Atlantic salmon stocks are re-established after eradication of the parasite. New methods are developed using chemicals that kill the parasite without killing fish in the rivers. Norwegian authorities have so far used more than NOK 1.5 billion on research, monitoring and combating G. salaris. However, the benefits are considered many times greater than the spending. Without control measures, G. salaris would likely have spread to new Atlantic salmon rivers where the same catastrophic outcome had to be expected. The Norwegian authorities seem to meet the goal in their long-term work to halt the spread of G. salaris and to eradicate the parasite in affected rivers.

Sphaerothecum destruens, the rosette agent, is a unicellular, obligate intracellular, mesomycetozoan pathogen at the phylogenetic intersection between animals and fungi (Combe et al., 2022; Paley et al., 2012). First associated with diseased North American (NA) salmonids, the parasite has increasingly been documented in European cyprinids where spread is attributed to introduction of the invasive East Asian topmouth gudgeon (Pseudorasbora parva) (Andreou et al., 2011; Arkush et al., 1998; Combe et al., 2022; Combe & Gozlan, 2018; Spikmans et al., 2019). Impacts of the parasite can be high, with mortalities exceeding 80% in diseased net pen reared chinook salmon (Onchorhynchus tshawytscha) (Harrell et al., 1986). However, infected chinook have lived 3–5 years and spawned successfully (Arkush et al., 1998). Losses among susceptible wild fish species are more difficult to document and the disease appears more insidious, resulting in low-level mortalities and population declines over time, including the disappearance of sunbleak (Leucaspius delineates) from much of Europe (Gozlan & Combe, 2023).

Formerly a D.R.I.P. clade member (Ragan et al., 1996), class Ichthyosporea, organisms were grouped according to shared morphological features and 18S rRNA molecular analyses (Gozlan & Combe, 2023). Members included Dermocystidium spp., the rosette agent, Ichthyophonus hoferi, and Psorospermium haeckeli (Ragan et al., 1996). Subsequent phylogenetic investigation reclassified the group under the class Mesomycetozoa (Herr et al., 1999; Mendoza et al., 2001, 2002), placing S. destruens, Dermocystidium spp. and Rhinosporidium seeberi in the order Dermocystida (Cavalier-Smith, 1998; Gozlan & Combe, 2023). Today, S. destruens is within the super-group Opisthokonta with eukaryotic fungi, choanoflagellates and animals (Gozlan & Combe, 2023).

The S. destruens lifecycle is poorly understood but includes distinctive 2–4 μm (undivided) and 4–6 μm (dividing) spores, and 2 μm uniflagellate zoospores (Arkush et al., 1998; Gozlan & Combe, 2023). Infection presumptively occurs through ingestion or adherence of motile zoospores to gills or skin, followed by asexual replication intracellularly in host tissues. Disease can be disseminated or nodular, corresponding to necrotizing lesions with numerous eosinophilic spores and little inflammation or with spores limited to granulomas primarily within visceral organs, respectively (Arkush et al., 1998). Cell rupture ultimately releases spores via bodily fluids. Zoosporulation, completed in freshwater, exhibits broad temperature toler

Piscine orthoreovirus-1 (PRV-1) is a prevalent agent in Atlantic salmon (Salmo salar) and the causative agent of heart and skeletal muscle inflammation (HSMI), an important disease in farmed Atlantic salmon. Investigations into the introduction and dissemination routes of PRV-1 in a field setting have been limited. This study aimed to better understand PRV-1 infections and HSMI-associated mortality under field conditions. We tracked introduction and spread of PRV-1 over one production cycle in a geographically isolated region in Norwegian aquaculture. From five sites, a total of 32 virus isolates were sequenced and genogrouped. The results indicated multiple introductions of PRV-1 to the area, but also revealed a high level of genetic homogeneity among the virus variants. The variants differed from that of the previous production cycle at two out of three sites investigated, suggesting that synchronized fallowing can be a useful tool for preventing dissemination of PRV-1 between generations of fish. Exposure to PRV-1 at the freshwater stage was identified as a potential source of introduction. A low level of HSMI-associated mortality was observed at all sites, with the onset of mortality showing some variation across PRV-1 genogroups. However, the study highlighted the complexity of associating viral genogroups with mortality in a field setting. Overall, this study contributes valuable insights into PRV-1 dynamics in a real-world aquaculture setting, offering potential strategies for disease management and prevention.