Journal of aquatic animal health最新文献

Objective: The objective of this study was to evaluate the potential influence of skeletal muscle mercury (Hg) concentrations on the biometric parameters and the frequency of lesions in Smallmouth Bass Micropterus dolomieu that were captured from three streams in Great Smoky Mountains National Park. By investigating the correlations between lesions, parasitism, and Hg concentrations, this study details the potential sublethal Hg contamination in fish in protected stream ecosystems.

Methods: Postmortem examinations with comprehensive histopathological analysis were performed on Smallmouth Bass (n = 62) that were collected from three streams in Great Smoky Mountains National Park, Abrams Creek (nAC = 27), Little River (nLR = 19), and Middle Prong Little Pigeon River (nMP = 16), from June to October 2022. Postmortem and histopathological data were matched to existing data on the concentrations of Hg in skeletal muscle to determine relationships between Hg concentration and pathology.

Results: Smallmouth Bass from Abrams Creek had higher total Hg concentrations, higher proportions of gill lesions, lymphohistiocytic epicarditis, and increased percentages of splenic pigmented macrophage aggregates but lower proportions of myxozoan cysts relative to the fish from other streams. Smallmouth Bass with high concentrations of Hg exhibited increased total length and body mass and more frequently showed the presence of glycogen-like vacuolation and increased pigmented macrophage aggregates in kidney tissue. Myxozoan cysts were more common in fish with lower total Hg levels, signifying the possible role of environmental impacts on myxozoan infection pressure.

Conclusions: These findings highlight the complex health profiles of Smallmouth Bass in a protected stream ecosystem, including high levels of Hg, parasitism, and lesions. Furthermore, this study underscores the importance of monitoring and mitigating heavy metal contaminants to safeguard wildlife health and recreational fishing resources.

Objective: Captive animals are exposed to various stressors originating from their artificial environment. Although stress can initially be an adaptive physiological response, persistent stress generally decreases immune function and makes animals more susceptible to pathogens. Environmental enrichment is a strategy that has been widely used to mitigate excessive stress and enhance animal welfare, but the effectiveness of individual enrichment components remains controversial. Hence, this study aimed to reveal the effect of shelter enrichment on stress levels and parasite infections in Masu Salmon Oncorhynchus masou. By using a single component, the study will help to provide a better understanding of the underlying mechanism of the enrichment effect.

Methods: We explored whether shelter-enriched conditions relieved stress in Masu Salmon by evaluating plasma cortisol levels. Fish provided with shelters were expected to experience less aggression from conspecifics and less stress from human disturbance. Moreover, we conducted a parasite challenge test using Ichthyobodo sp. to determine whether the presence of shelters inhibited infection by mitigating stress levels.

Results: Fish in enriched tanks had significantly lower basal cortisol levels than those in control tanks, suggesting that they were less affected by stressors. Although the difference was not significant, fish in enriched tanks also tended to experience less infection by the parasites than fish in control tanks.

Conclusions: Given these results, simple shelter enrichment appears to be an effective method for mitigating stress among captive fish and reducing stress intensity or frequency. In addition, shelter enrichment could be used to inhibit infectious diseases, although further work is needed to prove the effect. These findings confirm that shelter enrichment has measurable effects on the factors related to fish welfare, which should encourage the adoption of enrichment in fish farms.

Objective: Myxosporean parasites are worldwide-distributed cnidarians that infect the organs and tissues of marine and freshwater organisms, primarily fish. Based on morphological peculiarities, two myxosporean species, Myxidium gadi and Ceratomyxa merlangi, from the gallbladder content of Whiting Merlangius merlangus inhabiting four sampling localities (Kocaeli, Sinop, Ordu, and Trabzon) along the Black Sea coast of Türkiye have been identified.

Methods: Concordant with the morphological data, the first phylogenetic analyses on the nucleotide sequences of 18S ribosomal DNA confirmed our Myxidium specimens to be M. gadi. This study also provided the first molecular data on C. merlangi, which appeared to be the closest species to C. cretensis and C. arcuata on the phylogenetic trees. The infection prevalence (%) and density values of each parasite species were calculated according to season and sampling localities of Whiting.

Results: Ceratomyxa merlangi had a higher overall prevalence value (39.6%) than M. gadi (25.7%). The density values of both parasite species ranged between 2+ and 3+ in all fish samples. When the infection indices in sampling localities were compared for both parasite species, C. merlangi and M. gadi had the highest infection prevalence values in Sinop samples (66.3%); the highest density of infection (3+) was recorded in Sinop samples for C. merlangi and in Ordu samples for M. gadi.

Conclusions: This study provides the first molecular data on M. gadi and C. merlangi, revealing their phylogenetic positions. In addition, seasonal and regional infection data for these species in the southern Black Sea region are reported for the first time, and it has been determined that both species can occur together.

Objective: Renibacterium salmoninarum, the causative agent of bacterial kidney disease, poses a major threat to both wild and aquaculture salmonid populations. Traditional detection methods typically involve lethal sampling to collect kidney tissues but are often impractical for species of conservation concern. This study evaluates nonlethal sampling techniques for detecting R. salmoninarum in Greenback Cutthroat Trout Oncorhynchus clarkii stomias by comparing mucus, blood, and ovarian fluid samples to conventional kidney tissue.

Methods: During the 2019 spawning season, we collected samples from 781 adult fish and tested for R. salmoninarum via direct fluorescent antibody test (DFAT) and quantitative polymerase chain reaction (qPCR).

Results: A total of 25 and 256 kidney tissues were positive by DFAT and qPCR, respectively. Of the three nonlethal samples tested, mucus swabs showed the highest percent correlation for detection with positive kidney tissues (DFAT = 47.6%, qPCR = 41.7%). Blood and ovarian fluid samples showed a lower percent correlation with positive kidney tissues (blood: DFAT = 12.0%, qPCR = 1.2%; ovarian fluid: DFAT = 12.5%, qPCR = 21.4%).

Conclusions: Our results suggest that nonlethal mucus swabbing could serve as a practical alternative for monitoring R. salmoninarum, especially in conservation efforts where minimizing fish mortality is critical.

Objective: We sought to establish a current understanding of the histopathology of bivalves following exposure to heavy metal and to standardize the related terminology and microscopic diagnostic techniques, highlight limitations that hinder understanding, and discuss future research perspectives.

Methods: We conducted a literature review, looking for studies that implemented histopathological analyses to describe the damage that is caused by heavy metal bioaccumulation. For further description, we categorized lesions as regressive, defensive, or progressive.

Results: We analyzed 49 articles that employed histopathological techniques to describe the morphological changes that are associated with heavy metal bioaccumulation in bivalves. Since the 1980s, a growing interest in understanding how heavy metals affect bivalves has been evident, given the increasing number of published articles. Most studies were descriptive, although some contained experimental methods. The descriptive studies described damage to the digestive gland, gonads, gills, and kidneys. Defensive lesions were the most common response in the literature, with inflammation events reported in most cases. Regressive and progressive lesions were also documented, with necrosis (regressive change) and fibrosis (progressive change) being the most commonly reported, although not always correctly identified using microscopy.

Conclusions: Histopathological studies on the effects of heavy metals on bivalve health are abundant, and the resulting morphologic lesions have been described extensively. However, most studies on heavy metal accumulation in bivalves have not followed a microscopic approach, focusing instead on using bivalves solely as sentinel or bioindicator species. A histopathologic evaluation is a common and important facet of pathologic analyses; however, we identified inconsistencies among diagnoses and misleading use of pathological terms. Therefore, we highlight the need to establish a systematic and standardized characterization of lesions at the microscopical level and their subsequent categorization to reduce the ambiguity of pathological descriptions. Implementing other methodological approaches in combination with histopathological analysis will improve our understanding of how heavy metals affect the health of bivalves.

Objective: This study presents a juvenile green sea turtle Chelonia mydas case of fishing line ingestion during artisanal fishing monitoring, highlighting the importance of imaging and complementary diagnostics in detecting clinical alterations and managing marine debris-related injuries.

Methods: During artisanal fishing monitoring in Rio Grande do Sul, Brazil, a juvenile green sea turtle with a protruding fishing line was captured. Clinical evaluation included physical examination, ultrasonography, radiography, and hematological-biochemical analyses (e.g., red blood cell count, hemoglobin, white blood cell count, urea).

Results: Radiography and ultrasonography revealed a fishing line extending consecutively through the oral cavity, esophagus, and stomach without associated hooks, enabling manual line removal. Hematological findings indicated systemic responses to gastrointestinal trauma-regenerative macrocytic anemia (red blood cell count = 0.18 × 10⁶/µL; hemoglobin = 8.3 g/dL; hematocrit = 25%; mean corpuscular volume = 1,388 fL), leukocytosis (white blood cell count = 10,600 cells/µL), and elevated urea (232.59 mg/dL), suggesting dehydration and catabolic stress. Coelomic fluid accumulation indicated localized inflammation, though intestinal motility remained intact. Successful manual extraction avoided surgical intervention.

Conclusions: This case underscores the role of diagnostic tools (imaging, hematology) in assessing debris-related health impacts in aquatic species. The findings align with broader evidence of fishing gear as a pervasive stressor in marine ecosystems, contributing to anemia, metabolic dysregulation, and inflammatory sequelae. This work emphasizes the need to integrate clinical diagnostics into fisheries management and expand health-monitoring protocols to address anthropogenic threats across aquatic taxa.

Objective: This study aimed to characterize the effects of Prochristianella sp. infection (Cestoda: Trypanorhyncha) in the Octopus maya, with focus on tissue pathology, immune response, and potential implications for host health.

Methods: Molecular analyses of 28S ribosomal DNA were performed to confirm the identity of collected parasites from the buccal mass of octopus hosts. Macro- and microscopic observations of O. maya tissues, hemocyte counts, and histological analyses were conducted to assess the damage caused by the infection. Comparisons were made between naturally infected octopuses from Río Lagartos, Yucatán (the affected group), and minimally infected octopuses from Campeche (the control group) to establish a reference baseline for health and tissue morphology.

Results: Prochristianella sp. 1 was the only parasitic species infecting the buccal mass of octopuses collected from Río Lagartos, contrasting with the absence of the parasite in octopuses from Campeche, which were used as a reference group to characterize the infection. The affected group exhibited an undescribed capsular structure on the superior mandibular muscle of the buccal mass, containing cestodes and mucus and associated with tissue alterations, such as fibrosis, hemocyte infiltration, and focal necrosis. These findings led to the provisional designation of this condition as "myocestodiasis in cephalopods."

Conclusions: This work provides new findings on helminth-induced pathologies, generating hypotheses about the underlying mechanisms in infected cephalopods. The study highlights the importance of multidisciplinary approaches to understanding host-parasite interactions. Furthermore, it lays the groundwork for managing and conserving the O. maya, an important marine resource of the Yucatán Peninsula.

Objective: Flavobacterium columnare is a common pathogen of Chinook Salmon Oncorhynchus tshawytscha in the Klamath River. Elevated water temperatures invoke congregation behavior within thermal refugia and are associated with columnaris disease. A flowing-water F. columnare challenge system was compared with the standard static-bath challenge as an initial step in simulating a riverine exposure.

Methods: Juvenile Chinook Salmon were exposed to 103 CFU/mL F. columnare for 20 h either in an aerated static bath or within a recirculation swim chamber set at one body length per second. Fish were held at a constant 20°C or exposed to short-term temperature fluctuations to a maximum of 24°C prior to the challenge. Mucus and gill samples were collected at the end of the 20-h challenge and from fish held up to 96 h postchallenge. Samples were assayed for detection of F. columnare by quantitative PCR and conventional plate culture method.

Results: In static-bath challenge groups, F. columnare was detected in asymptomatic (38%) and moribund Chinook Salmon (29%). In contrast, F. columnare was detected in only one asymptomatic (4%) and one moribund (4%) Chinook Salmon in the flowing-water challenge groups. Prechallenge temperature conditions had no effect on infection. Other yellow-pigmented bacteria were isolated from the Chinook Salmon (particularly static-bath challenge) but were not associated with morbidity or amplified in the F. columnare quantitative PCR.

Conclusions: Low transmission of F. columnare occurred among juvenile Chinook Salmon under flowing-water conditions simulating a thermal refugia during early summer (20°C, flow of one body length per second, 20-h exposure to 103 CFU/mL). The flowing-water system is sufficient to examine the environmental factors (velocity, temperature, host density, duration, and bacterial concentration of exposure) of riverine exposures on F. columnare transmission to juvenile Chinook Salmon.

Objective: We investigated viral hemorrhagic septicemia virus dynamics in wild fish populations of the St. Lawrence River to compare host competency among five abundant native species and the invasive Round Goby Neogobius melanostomus following two decades of host-pathogen coevolution. To examine species' responses to the virus and identify principal hosts as viral reservoir species, we used viral surveillance among Round Gobies, Yellow Perch Perca flavescens, Rock Bass Ambloplites rupestris, Pumpkinseed Lepomis gibbosus, Bluegill L. macrochirus, and Brown Bullhead Ameiurus nebulosus collected from the nearshore fish community in the upper St. Lawrence River during spring 2020-2021.

Methods: Reverse-transcription quantitative PCR was used to detect and quantify viral nucleoprotein gene genetic material in pooled organ (i.e., liver, kidney, and spleen) and brain tissues of wild fish belonging to several susceptible host species.

Results: Reverse-transcription quantitative PCR detected viral hemorrhagic septicemia virus genetic material in each species during both sampling years. There was significant variation between species in both infection prevalence and median viral titer. Invasive Round Gobies exhibited significantly higher prevalence and titers compared to any of the native species. However, some native fishes (e.g., Yellow Perch and sunfishes Lepomis spp.) presented higher infection prevalence and viral concentrations compared to the others (e.g., Rock Bass and Brown Bullhead).

Conclusions: Multiple species remain susceptible to viral hemorrhagic septicemia virus under enzootic conditions; however, viral infections are distributed unevenly among host species. Invasive Round Gobies have amplified reservoir competence compared to native fish species.

Objective: The Spotted Scat Scatophagus argus, particularly in aquaculture, is commonly affected by intestinal parasitic infections that impact its health and growth. Filisoma spp., an acanthocephalan parasite, and Cryptosporidium spp. cause intestinal inflammation in various marine fish; however, infections with Cryptosporidium spp. or co-infection with these parasites have not been identified in Spotted Scat.

Methods: Host-parasite interactions in fish, including the inflammatory responses of the intestine, were investigated in 32 cultured Spotted Scat from Songkhla, Thailand. The study used parasitological examination, including polymerase chain reaction and nucleotide sequencing of the ITS1 and ITS2 regions of the ribosomal RNA gene for acanthocephalans and the 18S ribosomal RNA gene for Cryptosporidium. Additionally, histopathology and immunohistochemistry for interleukin-4 expression were performed.

Results: Most of the infected fish showed no significant clinical signs, with postmortem findings of hemorrhagic, congested, and edematous intestines. Parasitological analysis revealed that 84.37% of the fish were infected, with 9.37% having a single helminth infection, 40.62% being infected with coccidia, 34.37% having mixed infections with both parasites, and 15.62% of the fish being free from intestinal parasites. Polymerase chain reaction and nucleotide sequencing indicated that F. argusum and C. bollandi were the parasites involved. Histopathology showed increased inflammatory cell infiltrations, particularly eosinophilic granule cells and mononuclear cells, as well as higher levels of histopathological changes (vascular congestion, tissue necrosis, and epithelial desquamation) in the single F. argusum infection and co-infection with F. argusum and C. bollandi compared with C. bollandi infection alone. Similarly, significantly elevated interleukin-4 expression in the intestines, indicating a strong proinflammatory immune response, was observed in these groups.

Conclusions: This study highlights the detrimental effects of F. argusum, regardless of whether it is a single or concomitant infection, which may impact the health of fish.