Journal of fish diseases最新文献

Blood flukes cause serious health issues for farmed bluefin tuna worldwide. Their infection severity has been assessed by counting adult flukes in heart flushes. However, Cardicola orientalis adults reside in blood vessels in the gills. The aim of this study was to assess species composition, prevalence and intensity of adult blood fluke infection in gill blood vessels of ranched Southern Bluefin Tuna, Thunnus maccoyii. Based on molecular analysis, out of 41 adult blood flukes found in the gills of the tuna, 32 flukes were confirmed to be C. forsteri, while only 1 fluke was C. orientalis. There was a significant relationship between the number of adult C. forsteri in the heart and in the gills, with the heart having significantly greater prevalence. The presence of adult C. forsteri in the gills can cause blockage of the gill blood vessels and have a significant effect on the host. Furthermore, the presence of adult C. forsteri in gill blood vessels may have implications for the diagnosis of the infection and in particular identification of a negative host. The presence of adult C. forsteri in gill blood vessels should be recorded in the species description and considered when assessing the effects of this parasite on the host.

In the Norwegian aquaculture industry, opercular shortening has been ranked as an important cause of increased mortality, reduced welfare and growth. The aim of this study was to gather experience-based knowledge from fish health personnel and production staff involved in the commercial production of farmed Atlantic salmon and rainbow trout. A total of 29 semi-structured interviews with a predefined list of questions on the topic of opercular shortening were conducted in the period 22.04.24 to 10.12.24. Results showed that participants reported aggressive behaviour due to underfeeding, with subsequent nipping of gill lids as the main cause of shortened opercula in farmed salmonids. Inadequate feed allocation of fry was perceived to be the most important risk factor for aggression, in addition to starving fry. The prevalence of opercular shortening in the freshwater phase was reported to be between 0% and 70%. Opercular shortening was typically first detected in fry between 2 and 5 g, but sometimes already during first feeding (0.5 g) and in alevins. Damaged gill tissue, reduced growth rates and increased mortality were suggested as consequences of shortened opercula. Sufficient feed allocation in fry stages, optimization of environmental conditions, reducing fish density and culling of small fry were reported as preventive measures, while culling affected fish was the sole mitigating measure.

Lactococcus garvieae infection significantly affects the health of the white shrimp, Penaeus vannamei, particularly under low salinity conditions (5 ppt). Despite being a euryhaline species, shrimp become more vulnerable to stressors when exposed to low salinity, which can lead to disease outbreaks in aquaculture systems. In this study, we conducted RNA-Seq analysis on hepatopancreatic tissue from shrimp exposed to both low salinity and L. garvieae. The differential transcript analysis revealed 294 transcripts: 234 upregulated and 60 downregulated in shrimp under combined stress conditions. Gene Ontology (GO) analysis indicated that many differentially expressed genes were linked to biological processes, particularly peptidase inhibitory and regulatory activities. Additionally, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the ECM-receptor interaction pathway was upregulated, while pathways related to gluconeogenesis and metabolism were downregulated. The ECM-receptor pathway involved critical genes such as integrin β PS3, laminin, collagen and thrombospondins (THBS). This research provides insights into the molecular responses of shrimp to L. garvieae infection and low salinity stress.

Elasmobranchs, including sharks and rays, are commonly housed in public aquariums due to their ecological significance and educational value. The common guitarfish (Rhinobatos rhinobatos), currently listed as 'Critically Endangered' by the IUCN, is particularly susceptible to population declines due to overfishing and bycatch. While generally considered robust, individuals in captivity may experience stress-related health issues, increasing their susceptibility to infectious diseases. This study investigates a mortality event affecting three 20-year-old guitarfish kept in a public aquarium. The fish exhibited respiratory distress and ataxia before sudden death. Necropsy findings included external hemorrhages and severe hemorrhagic enteritis. Bacteriological analyses identified Photobacterium damselae subsp. damselae in all specimens through MALDI-TOF and PCR sequencing, while parasitological tests and RT-PCR for Betanodavirus were negative. Histopathology revealed bacterial aggregates in the gills, heart and kidney, consistent with systemic bacterial septicemia. P. damselae subsp. damselae is an opportunistic marine pathogen known to cause hemorrhagic septicemia in various fish species. This case represents the first documented occurrence of fatal P. damselae subsp. damselae septicemia in captive guitarfish. Understanding the impact of infectious diseases in confined environments is essential for improving the health management of endangered elasmobranchs in aquariums and conservation programs.

Adult salmon enteritis (ASE), characterised by severe ulcerative enteritis, has been linked to prespawn mortality (PSM) in spring Chinook salmon (Oncorhynchus tshawytscha) in certain rivers in Oregon, USA. Catastrophic losses of spring Chinook salmon have resulted from PSM, a significant threat to their population stability. Understanding the causes of ASE is therefore critical for mitigating PSM and supporting conservation. This study investigates the potential infectious aetiology of ASE using a juvenile Chinook salmon model. Fish were immunocompromised with dexamethasone implants, fasted, and exposed to intestinal tissues from ASE-affected adult Chinook. Histopathology of recipient fish revealed mid-intestinal lesions consistent with ASE. The microsporidium Enterocytozoon schreckii, which is observed in ASE-affected adults from rivers, was transmitted for the first time to juvenile Chinook Salmon, making E. schreckii a potential new pathogen of juvenile salmon. Additionally, intranuclear inclusions were identified in enterocytes by histopathology and viral particles were detected by electron microscopy in recipient fish. The study demonstrates that intestinal lesions consistent with ASE can be experimentally induced in juvenile Chinook salmon through oral exposure to infected tissues, supporting an infectious aetiology. Further research is needed to isolate specific pathogens, including viruses and E. schreckii, and to elucidate their roles in ASE development.

Mariculture, a significant component of the maritime industry that focuses on marine food production, faces challenges in maintaining productivity during bacterial disease outbreaks, particularly in high-value aquaculture such as the four-finger threadfin fish in Taiwan. Streptococcosis, caused by Streptococcus iniae, is a major contributor to the mortality of the four-finger threadfin (Eleutheronema tetradactylum). Recurrent streptococcosis outbreaks have highlighted the pressing need for highly effective vaccination strategies. Given its safety, environmental friendliness, and protective effects, vaccination is widely acknowledged as an effective means of preventing aquatic diseases. An innovative approach involves using biofilm-forming S. iniae as vaccine candidates for aquaculture. This study presents an effective approach for developing a biofilm-based vaccine by cultivating S. iniae on chitosan particles, facilitating robust biofilm formation and enhancing immune responses in four-finger threadfin fish. For comparison, a formalin-killed cell (FKC) vaccine, prepared from whole-cell S. iniae, was evaluated. Immune responses were examined in the blood, mucus, and gut lavage from both the vaccinated and control groups. These responses include immune-related gene expression, antibody titers, and lysozyme activity. At 30 days post-vaccination, the biofilm vaccine group exhibited elevated antibody titers, with values of 0.23 ± 0.02 in serum, 0.09 ± 0.01 in mucus, and 0.16 ± 0.01 in gut lavage. Following vaccination, both the FKC and biofilm vaccines significantly upregulated the expression of key proinflammatory cytokines (tumour necrosis factor-α, interleukin [IL]-10, IL-12) in the spleen and kidney, indicating robust activation of the innate immune response. However, the biofilm vaccine induced markedly higher expression of these cytokines, highlighting its stronger stimulation of innate immune responses. These results suggest that the biofilm-based formulation stimulates early immune signalling pathways that are critical for protection against S. iniae infection. In the challenge experiments, the relative percent survival was of 22.85% for the biofilm and 42.8% for the FKC vaccine groups. This study demonstrates that while both FKC and biofilm vaccines activated innate and adaptive immunity, the FKC vaccine provided higher protection (RPS 42.8% vs. 22.85%), indicating that strong immunogenicity does not always translate into effective protection and that oral vaccine strategies require further refinement. Further optimisation of oral vaccine formulations is required to improve the protective efficacy of biofilm-based vaccines in aquaculture.

Rock bream iridovirus (RBIV), a member of the Megalocytivirus genus, causes systemic infection and high mortality in rock bream (Oplegnathus fasciatus). Although enlarged basophilic cells are diagnostically relevant, their developmental trajectory and structural changes remain insufficiently characterised. This study provides the first quantitative morphometric and cytological characterisation of these cells, focusing on cytoplasmic and nuclear alterations, multinucleation and anucleation. Following oral administration of virus-containing tissue (200 mg; 6.12 × 10⁸ MCP copies), enlarged basophilic cells appeared from 11 dpi, only in fish with viral loads > 10⁶ copies/mg. Among 1664 cells analysed, mononucleate (A-1), multinucleated (two nuclei) (A-2), multinucleated (three nuclei) (A-3) and anucleate (B) types were identified. Mononucleate cells predominated at lower viral loads (over 83.1%), whereas anucleate cells comprised > 39.9% at higher loads. Exceptionally large cells with cytoplasmic axes of 50-60 μm were frequently observed. Cell and nuclear dimensions increased progressively with viral load, and multinucleate and anucleate forms predominated in fish with higher viral burdens. A schematic sequence of morphological progression from nuclear enlargement to nuclear loss is proposed as a working model, based solely on morphological evidence. Our study provides the first quantitative description of RBIV-induced enlarged basophilic cells and establishes a morphometric framework for future investigations into RBIV pathogenesis.

Aeromonas veronii, a prevalent Gram-negative bacterium in aquaculture, poses significant health risks to economically important freshwater fish species such as largemouth bass (Micropterus salmoides). This study investigates the role of pyroptosis, a highly inflammatory programmed cell death, in the immune response of largemouth bass to A. veronii infection. We characterised key pyroptosis-associated proteins, MsGSDMEa and MsGSDMEb, which harbour two conserved Gasdermin domains and are crucial in mediating pyroptosis. Following A. veronii infection, largemouth bass exhibited a robust upregulation of inflammatory cytokines (IL-1β, IL-8, TNF-α) and increased lactate dehydrogenase (LDH) activity in serum, indicating extensive cellular damage and inflammation. Quantitative real-time PCR analysis revealed a significant upregulation of pyroptosis-related genes, including NLRP3, ASC, and caspases (Caspase-1/-3/-7), in both spleen tissue and GF-1 cell line post-infection. Western blot analysis confirmed the cleavage of GSDME, a critical step in pyroptosis execution. These findings underscore the role of pyroptosis in the immune response of largemouth bass to A. veronii infection and suggest that modulating pyroptosis could be a potential strategy for disease management in freshwater fish species.

This study assessed the functional potential of autochthonous lactic acid bacteria isolated from the gastrointestinal tract of tambaqui (Colossoma macropomum) as larviculture probiotics. Five strains were selected and identified as belonging to the genus Weissella. In vitro assays revealed high tolerance to acidic pH (2.0-3.0), resistance to bile salts (10%), biofilm formation capacity, hydrophobicity and direct Aeromonas hydrophila inhibition. In in vivo tests, strains M13 and M14 promoted significant increases in tambaqui survival (72.2% and 68.7%; p < 0.05) and growth (standard length and eye diameter), as well as water quality (nitrite reduction), highlighting multiple beneficial effects. Innate immunity was activated, with total protein level (I3 and M14) and agglutinating titre (M13 and M14) increases. Intestinal colonisation was confirmed by bacterial counts, and the observed effects were consistent with adhesive and antimicrobial strain properties. The findings demonstrate a synergistic interaction between probiotics, hosts and pathogens, with integrated health, performance and environmental stability benefits. Strains M13 and M14 are, thus, promising alternatives to the use of antibiotics in intensive aquaculture systems, contributing to sustainable and safe tropical fish production strategies.

Mycobacterium ulcerans pseudoshottsii is a mycolactone-producing bacterium previously isolated from Striped Bass (Morone saxatilis (Walbaum)) from Chesapeake Bay and adjacent waters of the Atlantic Coast of North America. We report the first molecular detection of this pathogen in the native Gulf strain of Morone saxatilis collected from the Pearl River, Mississippi (USA). Molecular identification was conducted using a novel PCR assay targeting the parA-625 intergenic spacer of the virulence-associated pMUM plasmid. The isolate was unambiguously assigned to M. u. pseudoshottsii based on diagnostic single nucleotide polymorphisms (SNPs) and phylogenetic analysis. This report expands the known range of M. u. pseudoshottsii to include Gulf Coast watersheds and highlights the need for enhanced surveillance in wild and aquacultured fish populations of the southern United States.