Diseases of aquatic organisms最新文献

Microcystis spp. blooms in fish ponds can lead to fluctuations in water parameters, and the microcystin-LR (MC-LR) toxin they produce may pose health risks for fish, as well as consumers. Hydrogen peroxide (H2O2) treatment has been demonstrated to reduce populations of Microcystis spp. in aquaculture ponds. This study conducted 2 trials to investigate whether these treatments result in the release of MC-LR under laboratory conditions. We applied 7 mg l-1 of H2O2 to a Microcystis sp. culture and assessed the MC-LR level post-treatment. In the first trial, no MC-LR was detected in the H2O2 treatment group nor the negative control group, while 0.933 ± 0.381 ppb of MC-LR was extracted from 2344230 Microcystis sp. cells in 5 ml of media stock in our positive control group (where all cells were destroyed). In our second trial, where we added almost 30 times more Microcystis sp. to the culture media (i.e. 64125000 cells in 5 ml of stock), 19.333 ± 0.742 ppb of MC-LR were detected in the positive control on average. At this concentration of algae, our negative control (no treatment) and our H2O2 treatment group had 16.933 ± 0.303 ppb and 16.933 ± 0.109 ppb of MC-LR, respectively. The toxin levels were similar between the treated and untreated groups, but significantly less than the positive control group (p = 0.003). The results suggest that 7 mg l-1 H2O2 treatment to Microcystis sp. did not increase the level of MC-LR in the solution, but MC-LR was also not removed by the treatment. The low-dose 7 mg l-1 H2O2 treatment against Microcystis sp. bloom is unlikely to cause extra toxin (MC-LR) release to the medium.

A novel dinoflagellate is described from bluegill Lepomis macrochirus, rock bass Ambloplites rupestris, largemouth bass Micropterus nigricans, and yellow perch Perca flavescens collected from Lundgren Lake and Townsend Flowage, Wisconsin, USA. A new genus, Dermisichthinium gen. nov., is established for this species, D. pseudosporum sp. nov., which produces white spots grossly similar to those caused by Ichthyophthirius multifiliis. Microscopically, however, the vegetative cysts of D. pseudosporum closely resemble Haidadinium ichthyophilum, a parasite of threespine stickleback Gasterosteus aculeatus. Haidadinium ichthyophilum was collected from Haida Gwaii, British Columbia, Canada, for morphological and molecular comparison. Molecular analysis of the small subunit (18S), large subunit (28S), and internal transcribed spacer rDNA regions supports the novel species description and erection of a new genus. Pairwise comparisons of partial 18S and 28S sequences revealed divergence levels approximately 3 times greater than those among congeneric suessiacean dinoflagellates. Dermisichthinium pseudosporum sp. nov. lacks a 25 bp insertion in 28S unique to H. ichthyophilum, providing a molecular character for distinguishing the 2 species and supporting their placement in separate genera. Phylogenetic analyses consistently place D. pseudosporum sp. nov. and H. ichthyophilum in distinct clades. This study enhances our understanding of parasitic dinoflagellate diversity, underscores the importance of integrating morphological, molecular, and other diagnostic characteristics in their taxonomic classification, and offers valuable diagnostic insight for fish health professionals and parasitologists encountering this unusual group of cyst-forming dinoflagellates.

Infectious pancreatic necrosis virus (IPNV) poses a significant economic threat to aquaculture, yet understanding of the host-virus interaction remains limited. This study investigates the impact of IPNV on proteasomal response within rainbow trout kidneys during both subclinical (5 days post-infection, dpi) and clinical (10 dpi) stages of infection. Our results reveal a biphasic response: an initial stimulation of proteasomal activity at 5 dpi followed by inhibition at 10 dpi. Transcript analysis of proteasomal subunits in individual fish shows predominantly a correlation between their expression and proteasomal activity at 5 dpi, but this correlation was not seen by 10 dpi. Additionally, it was observed that the upregulation of immunoproteasome subunits by gamma interferon (γIFN) did not consistently cause a rise in proteasomal activity. Notably, a significant increase in free ubiquitin and ubiquitinated proteins was detected at 5 dpi, followed by a decrease at 10 dpi, indicative of dynamic changes in protein degradation, which agrees with proteasomal activity. The biphasic proteasome response suggests that early activation aids viral protein clearance, while later inhibition triggers cellular stress, potentially driving symptom development. Overall, this study underscores the significant impact of IPNV on proteasome activity in rainbow trout.

Ergasilids are an important group of parasitic copepods that occur globally in some coastal, estuarine, and freshwater habitats, including the south coast of the island of Newfoundland, Canada. Generally, males and developing females are not parasitic and remain in plankton. Adult females, however, become parasitic and seek a host following mating. Few studies have focused on detection and/or quantification of planktonic stages, and of those, all have utilized microscopic techniques. This method is time consuming and dependent on a specific parasitological skill set. In recent years, quantitative PCR (qPCR) techniques have become common in the detection and relative quantification of various invertebrate larval stages within plankton, including many metazoan parasites. In the present study, a qPCR assay using TaqMan™ minor groove binder probe technology, based on the Ergasilus labracis mitochondrial cytochrome c oxidase subunit I sequence, was developed for the first time to detect this parasite in mixed plankton samples taken near active salmonid aquaculture sites in a Northwest Atlantic coastal estuary. Ultimately, the technique can be used for tracking seasonal variability and abundance of planktonic stages of this parasite and thus illustrate patterns of seasonal infestation for both wild and cultured species in this region.

Protozoan parasites Perkinsus marinus (dermo) and Haplosporidium nelsoni (MSX) are associated with extensive epizootic mortality in eastern oyster Crassostrea virginica populations along the coastlines of the Atlantic Ocean and Gulf of Mexico. For decades, both diseases have resulted in substantial losses to ecological functioning of natural oyster habitat and have undermined the economic stability of wild oyster fisheries and mariculture industries in the USA. Both pathogens are widespread in coastal Georgia and are established regionally within native oyster populations, yet a clear timeline of transmission is not defined. Here, high frequency sampling was used to investigate when disease transmission is most probable relative to oyster lifecycle stage based in a localized region of the South Atlantic Bight (SAB). Dermo was present in the water column throughout the year with peaks in abundance concurrent with spawning activity, resulting in significant positive correlations among P. marinus concentration and the number of spawning females, egg yield, and shell height per spawning female. Detection of MSX in water samples appeared during 3 punctuated periods throughout the year but was not significantly associated with any environmental or life cycle metric. Overall, this research indicates that spawning events may be a mechanism for P. marinus transmission in oyster populations of the SAB.

Ostreid herpesvirus-1 (OsHV-1) is a threat to the global production of Pacific oysters Crassostrea gigas, often resulting in nearly complete mortality in affected stocks. A sentinel monitoring program was conducted between June and October 2020, to characterize OsHV-1 outbreaks in Pacific oysters along the west coast of the USA. Deployment of sentinel oysters at 5 commercial growing locations, coupled with frequent sampling, allowed measurement of the spatial and temporal occurrence of OsHV-1 outbreaks as well as the viral load and pathogenesis of OsHV-1 during C. gigas mortality events. In addition, 2 divergent oyster families were deployed at sites that have historically tested positive for OsHV-1 to measure the effect of oyster genotype on the severity of OsHV-1-induced mortality in the field. Mortality events at California test sites were associated with elevated levels of OsHV-1 in oyster tissue. OsHV-1 was not detected in oysters at Oregon and Washington test sites. In Tomales Bay, California, high variation among replicate culture units was observed in cumulative field survival and peak viral load. A negative relationship was observed between peak OsHV-1 load in oyster tissues and shell height at the time of peak viral load, suggesting larger seed may be less vulnerable during periods of OsHV-1 infection risk. Cumulative survival over the duration of the growing season in Tomales Bay was related to peak viral load and differed by family. These results corroborate previous findings suggesting selective breeding may effectively increase survival of oyster families during OsHV-1 outbreaks along the US west coast.

Globally, Marteilia spp. parasites have been associated with significant mass mortality events in populations of commercially important bivalve molluscs, frequently resulting in large-scale fishery collapses and substantial socio-economic impacts. The Wash Estuary, UK, supports several bivalve fisheries, and among these, common cockles Cerastoderma edule have suffered unusually high mortalities since 2008. We investigate potential causes of these mortalities, and confirm infection with M. cocosarum, strongly associated with cockle moribundity, also confirming its presence in archived samples collected in 2009. Molecular and light microscopy screening of samples collected during mortality events in 2021, including healthy (buried) and moribund (weak, unable to bury) cockles, indicated high prevalence of M. cocosarum in moribund cockles (PCR incidence up to 95%) in contrast to healthy cockles (up to 42%), suggesting an association between cockle moribundity and Marteilia infection. Analysis of the full ribosomal RNA array identified consistently different nucleotides between M. cocosarum infections in the Wash (denoted as genotype WE1) and those in Wales (denoted genotype WA1). A total of 83% of infections in the Wash could be identified as M. cocosarum WE1 and 12% as M. cocosarum WA1, with both genotypes recovered from 5% of infected animals. Histopathologically, M. cocosarum WE1 infects the gill, mantle and connective tissues, identical to observations of M. cocosarum infecting Welsh cockles. Ongoing cockle mortalities in the Wash raise concerns regarding the sustainability of this resource ecologically and economically. Additional measures may be required to reduce the spread of this pathogen, noting that its distribution beyond the Wash and Wales is currently unknown.

Understanding the role of environmental factors such as pollution and infectious diseases on the health and well-being of free-ranging beluga whales Delphinapterus leucas is essential for their conservation. As part of this effort, 2 novel papillomaviruses (PVs) were identified in urogenital swabs of 2 free-ranging female beluga whales in Bristol Bay, Alaska, USA. Their genomes were 7825 and 7713 nucleotides (nt) in length with 84.6% nt and 82.5% amino acid identities for the L1 gene, generally used for classifying papillomaviruses. Both PV genomes contained an early region of E6, E1, E2 and E4 genes, a late region containing L2 and L1 genes, and a non-coding regulatory region. The carboxy end of the E6 oncoprotein of both PVs did not contain the PDZ-binding motif, known to have a strong correlation with oncogenicity. BLAST NCBI nt analyses of the L1 gene of 1 PV revealed highest identity (91.2%) with a PV of a short-beaked common dolphin Delphinus delphis, while the other PV showed highest identity (85.5%) with a PV from a Yangtze River finless porpoise Neophocaena asiaeorientalis. The PVs identified in this study share the highest identity with PV members of the genus Upsilonpapillomavirus, subfamily Firstpapillomavirinae, family Papillomaviridae. Also, 2 herpesviruses were isolated in primary beluga whale kidney cell cultures and identified by sequencing the glycoprotein B and E genes. Both herpesviruses corresponded to the species Varicellovirus monodontidalpha1. Our findings confirm the necessity to expand studies on the occurrence, dissemination and virus diversity that may be adversely affecting the well-being and preservation of beluga whales in Alaska.

The fluted kidneyshell Ptychobranchus subtentus is an endangered freshwater mussel that, as of 2012, has experienced nearly 70% decline from its historical range in the Cumberland and Tennessee River drainages of the southeastern USA. Understanding the factors contributing to morbidity and mortality is essential for the long-term conservation of the species and the development of effective recovery plans. In this study, we incorporated morphological, histological, and molecular techniques to identify and describe parasites and associated lesions in 18 P. subtentus collected from the Clinch River, USA, in 2018 and 2021-2023. We identified several parasites, including metacercariae of Homalometron sp. (Homalometridae; 6/7 case mussels, 7/11 controls), sporocysts of putative Phyllodistomum sp. (Gorgoderidae; 4/7 case mussels, 2/11 controls), adult Aspidogastridae, and gonadotropic microsporidia (2/7 case mussels, 6/11 controls). Notably, this is the first report of P. subtentus as the first intermediate host for Phyllodistomum sp. and second intermediate host for Homalometron sp. Additionally, we report the first documentation of Unionicola sp. mites and gonadotropic microsporidia in P. subtentus. Our findings contribute to the understanding of parasites in mussel populations and emphasize the need for further research on the role of parasitism in mussel mortality, especially in endangered species.

To better understand the relative contributions of sea lice Lepeophtheirus salmonis and Caligus clemensi from farmed and non-farmed sources, infestations with sea lice are described on juvenile chum salmon Oncorhynchus keta and pink salmon O. gorbuscha from the Broughton Archipelago (BA) in coastal British Columbia, Canada, during a period of declining salmon aquaculture presence. A total of 2868 salmon were collected by beach seine from 14 sites between 2016 and 2024 and examined for sea lice infestation by microscope. During this time, production of Atlantic salmon in open netpens in the BA declined from a high of 21645 metric tonnes (t) in 17 facilities in 2019 to 614 t in 2 facilities in 2024. The annual prevalence of all sea lice on chum salmon ranged from 53.7% in 2022 to 12.5% in 2023 and on pink salmon from 62.9% in 2022 to 7.3% in 2023. In 2024, the prevalence of L. salmonis and C. clemensi on both salmon species increased and was similar to or higher than annual prevalence values measured between 2016 and 2021, indicating the importance of natural reservoirs as sources of sea lice infestation in the BA.