This study analysed published data on the distributions of minimum inhibitory concentrations of a group of freshwater isolates classified as Aeromonas spp. with the aim of establishing whether they provided any evidence that epidemiological cut-off values set from these data would be unreliable. This group contained 233 isolates and included members of at least 11 species. The standard deviations (SDs) of the wild-type distributions for 10 antimicrobial agents were calculated for this multi-species group using the ECOFFinder and normalised resistance interpretation (NRI) algorithms. These were compared to the SDs of 110 distributions established for individual species published by the European Committee on Antimicrobial Susceptibility Testing. Fifty-one of these distributions had been generated by multiple laboratories and 59 by single laboratories. When the ECOFFinder algorithm was used to calculate the SDs, the mean for the multi-species group was 0.63 log2 µg ml-1, and the 51 individual species and multiple-laboratory groups were 0.68 and 0.65 log2 µg ml-1, respectively. When the NRI algorithm was used, the mean for the multi-species group was 0.79 log2 µg ml-1, and the 51 individual species and multiple-laboratory groups were 0.79 and 0.76 log2 µg ml-1, respectively. These comparisons indicate that the heterogeneity in the susceptibility to antimicrobial agents within the multi-species group of Aeromonas is not significantly different from that recorded for individual species. This analysis, therefore, suggests that epidemiological cut-off values designed to be applied to all members of the genus Aeromonas would not be inherently unreliable.

Mycobacteria infections are sporadically documented in wild sea turtles and are generally regarded as opportunistic pathogens. This case series describes infections by a Mycobacterium ulcerans ecovar in 2 imperiled species of sea turtle, the Kemp's ridley Lepidochelys kempii (n = 5) and loggerhead turtle Caretta caretta (n = 1). Most cases were stranded animals that presented with neurological abnormalities resulting from severe mycobacterial meningoencephalitis. In 4 instances, infected turtles were found in relative proximity to one another and without evident predisposing conditions, suggesting the potential for broader population health significance. Lesions were predominantly heterophilic and histiocytic, and were characterized by extensive leukocytic necrosis, absence of organized granuloma formation within the nervous system, fibrinoid vascular necrosis, and myriad extracellular and intrahistiocytic acid-fast bacilli. Except for one severely bacteremic animal, involvement of visceral organs was relatively mild and often paucibacterial. Multiple genetic loci were 100% identical in all 6 affected turtles and to multiple reported M. ulcerans ecovars; an ITS2 sequence amplified from each turtle was 100% identical only to M. pseudoshottsii, a pathogen of wild and farmed fish. The genetic relatedness of the organism to M. ulcerans ecovars known to produce mycolactones (polyketide toxins) suggests that the distinct pathological features among these cases are the result of a mycolactone-producing species of mycobacteria. This is the first report of M. ulcerans ecovar infection of a reptile. Mycobacterial meningoencephalitis should be considered as a differential etiological diagnosis for neurological disease in wild sea turtles.

Two supersaturation events caused gas bubble disease (GBD) in captive Melibe leonina (lion's mane sea slugs). For the first event (a), supersaturation spikes (114-127% total dissolved gas [TDG]) occurred on Days 1a, 4a, and 23a. On Day 5a, nearly all 77 animals developed grossly visible gas bubbles within vasculature. Two recompression treatments were performed on 2 cohorts: (1) 7 animals were placed at 8.5 m depth (103 kPa) and unmonitored for 5 d, after which they had resolution of gas bubbles; and (2) 12 animals were placed in a hyperbaric chamber (152 kPa) for 5 d and had resolution of gas bubbles within 2 h of treatment initiation. Untreated animals had slow, consistent improvement with complete resolution at Day 12a. Starting on Day 23a (date of a supersaturation spike) through Day 79a, 0-4 animals died per day, totaling 60 deaths (78% mortality), after which no further mortalities occurred. After the first supersaturation event, 17 animals remained, and 16 new animals were added to the tank. Two months later, during the second event (b), supersaturation spikes (106-110% TDG) occurred on Days 1b, 2b, and 6b-15b. On Day 15b, all M. leonina developed grossly visible bubbles and were placed in a hyperbaric chamber for 14 d; gas bubbles resolved, and no mortalities occurred in the second event. Histologically, gas emboli were in the hemolymphatic sinuses and caused soft tissue edema. The cause for GBD was unknown for the first event and, for the second event, was due to cracked plumbing valves.

This work was performed to generate the data needed to set epidemiological cut-off values for inhibition zone data of 8 antimicrobial agents against Vibrio parahaemolyticus determined using standardised disc diffusion protocols with incubation at 35 ± 2°C for 16 to 20 h and at 28 ± 2°C for 24 to 28 h. The zone diameter data aggregated from 3 to 5 laboratories were analysed by the normalised resistance interpretation algorithm. Cut-off values calculated from data obtained at 35 and 28°C were ≥23 and ≥24 mm for ceftazidime, ≥18 and ≥20 mm for enrofloxacin, ≥28 and ≥29 mm for florfenicol, ≥14 and ≥14 mm for gentamicin, ≥29 and ≥32 mm for meropenem, ≥17 and ≥18 mm for oxolinic acid, ≥22 and ≥24 mm for oxytetracycline, as well as ≥19 and ≥21 mm for trimethoprim/sulfamethoxazole. The influence of the incubation temperature on inhibition zone sizes was investigated by calculating the difference between the zones obtained at 35 and 28°C for a specific antimicrobial agent with a particular isolate by an individual laboratory. The mean of the differences calculated for 1314 paired observations was 0.38 mm with a standard deviation of 2.68 mm. The data generated in this work will be submitted to the Clinical and Laboratory Standards Institute and the European Committee on Antimicrobial Susceptibility Testing for consideration in their setting of internationally agreed-upon epidemiological cut-off values for V. parahaemolyticus that are essential for interpreting antimicrobial susceptibility testing data of this species.

Edwardsiella ictaluri is a pathogenic bacterium that poses a significant threat to the economic viability of aquaculture. However, the effects of E. ictaluri infection on the non-specific immune response of hybrid grouper and the regulatory mechanisms of oligochitosan in modulating the infection are poorly understood. We investigated the impact of oligochitosan supplementation on the growth performance, biochemical parameters, immune response, and apoptosis in hybrid grouper infected with E. ictaluri. The results showed that oligochitosan significantly improved the weight and length of hybrid grouper, whereas E. ictaluri infection reduced their growth performance. Histopathological analysis of the head kidney showed no significant differences among the groups. Biochemical analysis revealed that E. ictaluri significantly increased the activity of serum glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT), while decreasing the activities of catalase (CAT) and superoxide dismutase (SOD), with oligochitosan ameliorating these effects. E. ictaluri infection also significantly elevated the GOT activity in the head kidney while reducing CAT and SOD activities. The analysis of inflammatory factor expression revealed that E. ictaluri significantly increased the levels of IL-8, TNF-α, and IKKα, whereas oligochitosan effectively decreased these inflammatory markers. Apoptosis gene expression analysis indicated that E. ictaluri infection significantly upregulated bax, caspase-3, and caspase-8, while supplementation with oligochitosan reduced their expression levels. TdT-mediated dUTP nick-end labeling signals were significantly increased following E. ictaluri infection, while supplementation with oligochitosan notably reduced them. In conclusion, oligochitosan can regulate growth, immune response, and apoptosis, potentially protecting hybrid grouper infected with E. ictaluri.

We tested the antiviral activity of aqueous extract of star anise Illicium verum (AEIV) against striped jack nervous necrosis virus (SJNNV) in vitro as well as in vivo using the Sahul Indian Seabass Spleen (SISS) cell line and Asian seabass Lates calcarifer. Preliminary results from GC-MS profiling and polyphenol content estimation of AEIV revealed the antiviral potential of the extract. Before testing the compound, the extract was assessed for its toxic potential in an in vitro model (SISS cell line) using 4 different concentrations (50, 75, 100 and 200 µg ml-1) of AEIV through MTT and neutral red assays. The tested concentrations were not toxic (≥90% survival). Subsequently, the same concentrations of AEIV were tested for their antiviral potential against SJNNV in SISS cells. The results showed that AEIV at higher concentration (100 and 200 µg ml-1) effectively inhibited SJNNV replication in the SISS cells. RT-PCR and qPCR confirmed the inhibition of the virus. The same concentrations were then used to evaluate their antiviral efficacy in vivo by intraperitoneal injection in Asian seabass. We observed 100% mortality only in the fish injected with SJNNV (control), which confirms that AEIV possesses the potency to control the replication of SJNNV under both in vitro and in vivo conditions. The present study indicates that medication with plant extracts having antiviral activity could be a potentially beneficial alternative to the usage of chemotherapeutics in aquaculture.

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.

Shellfish fisheries and aquaculture within the Chesapeake Bay (hereafter 'the Bay') and its tributaries have been historically impacted by disease and climate events. Climate-driven shifts in temperature and salinity can alter host-parasite dynamics, influencing outbreaks. Here, we explore the relationship between temperature, salinity and parasite distribution and abundance in the eastern oyster Crassostrea virginica-Perkinsus marinus system. We use long-term (30 yr) environmental data and P. marinus surveys in the Bay to identify (1) how climate affects P. marinus prevalence and intensity, (2) seasonal and climate-driven infection patterns, and (3) regional environmental influences on disease. We found significant relationships between P. marinus infection intensity, prevalence, increasing temperature and decreasing salinity. Our results indicated that there is an overall decreased abundance of P. marinus prevalence and intensity throughout the Bay driven by decreases in salinity over time, most prominently from 2003-2020. However, these temporal trends in prevalence and intensity vary largely by region, with some regions still experiencing high disease burden. Examining monthly environmental parameters reinforced the dominant role of salinity in driving disease patterns. Salinity had significant relationships with prevalence and intensity year-round, with the largest effects in late spring/early summer. Monthly temperatures had fewer significant relationships to prevalence and intensity, but the largest significant effects were seen in late winter/early spring. Notably, this study is the first to document that winter salinity influences fall parasite prevalence, sometimes exerting a greater effect than temperature. Continued and expanded monitoring of marine disease is crucial to understand how the changing climate is impacting disease.

Emerging infectious diseases (EIDs) pose a major threat to global amphibian populations, contributing to widespread mortality and species extinctions. Among EIDs, those caused by the fungal pathogens Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal), and viruses in the genus Ranavirus (Rv), represent the most significant threats to amphibian biodiversity. Here, we tested for occurrence of Rv in 3 different locations in southeastern Sweden. Using a quantitative PCR assay, complemented by a secondary PCR-based validation method targeting the viral major capsid protein gene and additional 5 partial sequences, we detected Rv in 2 of 3 locations and in 5 out of 43 individuals tested. This is the first record of Rv occurrence reported at such high latitudes in northern Europe and the first from the Scandinavian peninsula, contributing important insights into infection prevalence in northern amphibian populations. These findings establish a basis for the conservation of vulnerable populations.

This report describes a severely emaciated adult female bottlenose dolphin Tursiops truncatus found dead in September 2021 with numerous traumatic injuries. The animal stranded in coastal Alabama, USA, a hotspot in the Gulf of Mexico for trauma-related marine mammal strandings. A combination of traditional and advanced diagnostic techniques including postmortem examination, histopathology, and computed tomography revealed trauma from multiple events, including rib and vertebral fractures of varying chronicity and a more recent catfish barb penetrating the diaphragm with associated tissue necrosis. Tooth growth layer group analysis indicated this individual was ~40 yr old, despite a total straight length notably less than is typically reported for an adult female T. truncatus in the region. Advanced age was also supported by tooth wear, evidence of multiple pregnancies, fusion of sternal bones, and age-related changes in the heart and liver. This case illustrates a multifactorial cause of death in a coastal bottlenose dolphin and highlights the value of combining traditional postmortem examination with advanced imaging techniques to more accurately determine cause of death in the presence of multiple traumatic injuries.

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.

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.

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.

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.

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.

NK-lysin is an effective antimicrobial peptide secreted by natural killer (NK) cells and cytotoxic T lymphocytes. Although numerous studies have been conducted on NK-lysin, its biological functions have not yet been comprehensively catalogued. In this study, a novel NK-lysin peptide, NKLj27, located in the SapB domain of Japanese seabass Lateolabrax japonicus, was identified and synthesized, and its antibacterial and chemotactic activities were investigated. Bioinformatic analyses showed that NKLj27 shared 66.67-79.17% sequence homology with known teleost NK-lysin peptides, and the spatial structure prediction of NKLj27 indicated that it was mainly composed of α-helices. A subsequent antibacterial assay demonstrated that NKLj27 exhibits potent activity against Staphylococcus aureus, Micrococcus luteus, Vibrio litoralis, V. alginolyticus, Listonella anguillarum, Escherichia coli, V. harveyi, and V. scophthalmi. During the interaction with V. alginolyticus, NKLj27 changed the cell membrane permeability, causing leakage of cellular contents, while the cell membrane structure remained basically intact; subsequently, NKLj27 penetrated into the cytoplasm and acted on bacterial nucleic acids. It first bound to bacterial genomic DNA and RNA, then caused their retardation and degradation, and following incubation, it changed the physical conformation of the DNA molecules. The in vivo experiments showed that NKLj27 significantly reduced V. alginolyticus load in fish tissues. At the cellular level, NKLj27 also exhibited chemotactic activity on epithelioma papulosum cyprini cells. In summary, these results provide new insights into the functions of NK-lysin peptides in teleosts and show the potential of using NKLj27 in aquaculture for bacterial disease control.

Domoic acid (DA) is a naturally occurring amino acid structurally analogous to kainic acid (KA). DA, a neurotoxin commonly associated with toxigenic Pseudo-nitzschia species, enters the food chain via filter feeders and poses a potential threat to predators such as sea stars. To assess the presence of DA, wild-collected sea stars (Pisaster ochraceus and Asterias spp.) were analyzed for DA. Although there were no signs of a recent Pseudo-nitzschia bloom prior to collection, both species had low levels of detectable DA, primarily concentrated in the pyloric caeca. DA concentrations in P. ochraceus tissues ranged from 0 to 1033 ng g-1 tissue, averaging (±SE) 614 ± 93 ng g-1 in pyloric caeca, and were negatively correlated with body mass. DA concentrations in Asterias spp. averaged 123 ± 34 ng g-1 in pyloric caeca. Subsequently, to assess neurotoxic impacts-behaviorally and physiologically-we challenged Asterias spp. with KA, as a stand-in for DA, using intraperitoneal injections of 0, 3, or 30 μg KA g-1 body mass. Immediately following exposure, 11 out of 12 sea stars injected with 30 μg KA g-1 failed to right themselves within 30 min and their arm circumference was reduced by 19.7 ± 3.5%. Righting time, but not arm circumference, recovered within 2 d. We hypothesize that these responses precipitated from KA binding to glutamate receptors in the mutable collagenous tissue. These findings reveal that DA accumulates in sea star tissues, and that KA can cause significant yet reversible behavioral changes, raising concerns about the impact of repeated, long-term, or higher-dose exposures of wild sea stars to these neurotoxins.

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.