Journal of fish diseases最新文献

Saprolegnia sp., a water mold causing significant economic losses in aquaculture, necessitates sustainable alternatives to chemical treatments. This study investigated the resinous exudate of Psoralea glandulosa and its derivatives as inhibitors of Saprolegnia parasitica and S. australis . Through in vitro assays and in silico molecular docking, the research aimed to determine the inhibitory efficacy and mechanism of action of these natural compounds. The results identified 3-hydroxybakuchiol (2) as the most potent agent. It demonstrated superior minimum inhibitory concentration (MIC) values of 50 μg/mL against S. parasitica and 25 μg/mL against S. australis , surpassing the commercial control, bronopol. Its minimum oomyceticidal concentration (MOC) was also confirmed at low levels (50-75 μg/mL). Molecular docking analysis revealed that compound 2 has a high binding affinity for two crucial proteins in Saprolegnia: host-targeting protein 1 (Htp-1) and plasma membrane ATPase. These findings suggest that compound 2 acts as a potent dual inhibitor, with its free hydroxyl group being critical for its activity. This study positions 3-hydroxybakuchiol as a promising lead compound for developing new, safer, natural-based therapies to control saprolegniasis in the aquaculture industry.

Vibrio infections cause enteritis in grouper fish, leading to high mortality and stunted growth, which is a major challenge for aquaculture. Oligochitosans, marine prebiotics with bioactive properties, have proven their potential for growth promotion and immune regulation. However, the impacts of Vibrio harveyi on the gut microbiome of grouper fish and the potential of oligochitosans to modulate these effects remain poorly understood. This study investigates the influence of oligochitosan on the gut morphology, microbiota and metabolic patterns of hybrid grouper following low-dose infection with V. harveyi. After 8 weeks of feeding, infected groupers exhibited histopathological changes in the intestine that were mitigated by oligochitosan, as evidenced by improved villus height and intestinal wall thickness. Microbiome sequencing revealed that oligochitosan enhanced α-diversity and shifted bacterial communities, particularly increasing the abundance of Fusobacteriota and Actinobacteriota. Furthermore, the prevalence of Shewanella and Vibrio, which were more abundant in infected groupers, was reduced upon oligochitosan treatment. Metabolomic analysis indicated that lipid metabolism pathways were significantly altered in response to infection and oligochitosan intervention. Overall, oligochitosan modulates the gut microbiome and metabolite profiles, potentially protecting against V. harveyi-induced intestinal dysbiosis and metabolic disorders in hybrid groupers.

The white spot syndrome virus (WSSV) is a major threat to shrimp farming and causes substantial economic losses in aquaculture. The VP28 envelope protein of WSSV facilitates initial systemic infection in shrimp. Although mammalian-derived antibodies are used for diagnostic tests, high costs and animal welfare concerns necessitate alternative strategies. This study produced specific yolk immunoglobulin (IgY) by immunising laying hens with the VP28 envelope protein as a cost-effective alternative for WSSV detection. IgY antibody titres and specificity were assessed using ELISA and western blotting, and their performance was compared with that of IgG rabbit antibodies. Stability was tested under various pH and salinity conditions. A time-course infectivity experiment analysed infection progression. Western blot analysis using IgY detected WSSV in shrimp samples at 6 h post-infection (h p.i.) in the haemolymph and eyestalk. By 12 h p.i., the gills, head soft tissue, appendages and other organs showed positive. Shrimp mortality occurred at 36 h p.i. Western blot findings matched those of IgG rabbit antibodies, proving that IgY antibodies were viable. Based on these findings, a validation study was conducted using 55 field samples collected from various regions of India. IgY serves as an innovative biological recognition component for early diagnosis of WSSV, offering an ethical and economical option for disease management in aquaculture.

Aeromonas hydrophila can cause disease in various aquatic animals, but there exist no effective alternatives to control its outbreak. In this study, diseased largemouth bass were collected from the breeding farm Lake Dahong (Chongqing, China), a strain SK-2 was isolated and identified as A. hydrophila. In order to investigate the pathogenicity of the strain and the protective efficacy of the inactivated vaccine, we firstly evaluated the virulence factors including hemolytic, proteolytic, and amylolytic activities. The results displayed that the diameters of hemolytic, proteolytic, and amylolytic circles reached 0.94 ± 0.10, 2.15 ± 0.16, and 1.51 ± 0.14 cm respectively. Median lethal dose (LD₅₀) was tested and the LD₅₀ value was calculated as 1.39 × 10⁵ CFU/g. Besides, a challenge test was conducted and two levels (LD₅₀ and 1/10 LD₅₀) were set for intraperitoneal injection. Significant immune responses were found in the serum and head kidney samples, with the higher superoxide dismutase (SOD), peroxidase (POD) and malondialdehyde (MDA) levels (p < 0.05). The results of qPCR revealed that tumour necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β) and interferon-γ (IFN-γ) expression levels were elevated in the liver and head kidney samples, reaching a stable state at 48 h. Furthermore, the inactivated vaccine of SK-2 was prepared using formalin and 0.85% saline (CG) and the inactivated vaccine of SK-2 (AHIV) was intraperitoneally injected for 28-d immunisation. The results indicated the SOD and lysozyme (LZM) activities in the serum of the AHIV group were dramatically higher (p < 0.05) than those in the CG group, the catalase (CAT) and MDA levels were remarkably increased (p < 0.05) compared with the CG group, and these immune-related genes exhibited conspicuous upregulation (p < 0.05), suggesting the inactivated vaccine of SK-2 could bring about subdued oxidative stress in the innate immunity of largemouth bass. The wide-type SK-2 was challenged into the largemouth bass post 28-d immunisation, and the relative protection was calculated as 86.21%. These findings provide theoretical support for the bacterial disease control of largemouth bass.

A previous study in our laboratory revealed that microRNA-33 (miR-33) regulated autophagy initiation and inflammatory response by targeting Atg5; furthermore, in this study, chloroquine (CQ), lipopolysaccharide (LPS) and the miR-33 inhibitor were transfected into Ctenopharyngodon idella kidney (CIK) cells to explore whether miR-33 regulated late-stage autophagy and inflammatory response induced by LPS. The results showed that CQ inhibited the fusion of autophagosome and lysosome and significantly increased the secretion of pro-inflammatory cytokines (p < 0.05). Interestingly, miR-33 was also significantly upregulated after CQ incubation (p < 0.05). However, compared with the CQ group, the expression of beclin-1, atg5, atg7 and atg12 did not recover after inhibiting miR-33 (p > 0.05). But the expression of tnf-α, il-6, il-1β, il-8 and nf-κb, as well as the secretion of TNF-α, IL-6, IL-12 and IL-1β, were significantly downregulated, and the activities of ALP, SOD and CAT were significantly increased (p < 0.05). Furthermore, CIK cells were treated with LPS to construct an inflammation model, and miR-33 expression was significantly upregulated (p < 0.05). In contrast, the miR-33 inhibitor reversed the effects of LPS by decreasing the transcription levels of tnf-α, il-6, il-1β, il-8 and nf-κb; inhibiting the secretion of TNF-α, IL-6, IL-12 and IL-1β; and increasing the activities of ACP, ALP, SOD and CAT (p < 0.05). Taken together, the inhibition of miR-33 alleviated inflammatory response in CIK cells induced by CQ and LPS, but miR-33 regulated autophagy independently of CQ. These findings provided a theoretical foundation and a novel perspective for further understanding the mechanisms by which miR-33 regulated autophagy and inflammation in fish.

Decapod iridescent virus 1 (DIV1) causes severe disease outbreaks in shrimp and crab culture areas. A simple, rapid, and visual DIV1 assay is important for the control of viral diseases. This study presented a novel DIV1 detection method that combines recombinase polymerase amplification (RPA) and lateral flow strip (LFS). After selecting primers and probes, we optimised the concentration of the reverse primers, reaction time, as well as reaction temperature of RPA-LFS detection. RPA can amplify the target gene within 18 min at a constant temperature of 38°C, and LFS can observe the amplification results within 3 min. Importantly, there is no cross-reactivity with other infectable shrimp viruses and pathogens, such as WSSV, IHHNV, TSV, EHP, CMNV, YHV, MrNV samples, as well as Vp_AHPND. In addition, RPA-LFS has high detection sensitivity, with a lower detection limit of 1.12 × 10¹ copies/μL. Using 110 field samples, the results of qPCR recommended by WOAH (OIE) and RPA-LFS were identical, indicating that RPA-LFS is as reliable as qPCR. The RPA-LFS assay is a valuable tool for the rapid and accurate detection of DIV1.

Infectious pancreatic necrosis virus (IPNV) can cause devastating disease in Atlantic salmon (Salmon salar). IPNV has a broad host range and may threaten other aquaculture species. Understanding interspecies transmission of IPNV is crucial for protecting the aquaculture industry. With the expansion of fish farming (in Norway), it is important to assess whether a pathogen can transmit from one fish species to another and cause disease. We investigated whether IPNV-infected Atlantic cod can shed IPNV, leading to infection in other fish important to Norwegian aquaculture: halibut, salmon and lumpfish, using the cohabitation experimental trial method. Virus shedding, transmission, fish mortality and pathology were assessed. We documented virus shedding in water and mortality in IPNV-injected Atlantic cod. No mortality was observed in the cohabitated fish species during the experimental period. We confirmed lesions consistent with IPN by histopathology and immunohistochemistry in IPNV-injected Atlantic cod and in IPNV-PCR positive cohabitant Atlantic halibut. Cohabitant Atlantic cod, Atlantic salmon, Atlantic halibut and lumpfish were also found positive for IPNV by PCR, suggesting that IPNV-infected Atlantic cod can transfer infection to other farmed fish species. These findings highlight the potential risk of pathogen spread among farmed fish species and demonstrate the importance of understanding infectious fish disease epidemiology.

This study reports the first confirmed case of Myxobolus koi parasitic infection in koi (Cyprinus carpio koi) imported into Thailand. Infected fish exhibit clinical signs during the quarantine process, including lethargy, tachypnea, flared gill opercula and excessive mucus production in the gills. The gross pathological findings included swollen and pale gills interspersed with white nodules. Microscopic examination of gill biopsies revealed mucus clumps and numerous pyriform myxospores, with no evidence of other parasites. Molecular analysis confirmed the presence of Myxobolus spp. DNA through PCR amplification targeting the 18S SSU rRNA. Phylogenetic analysis of 776 bp sequences from our representative isolates (CU01, CU02 and CU03) revealed 100% nucleotide identity with M. koi sequences from goldfish in China (OM757920) and koi in the USA (FJ841887), which formed a distinct clade with strong bootstrap support. Haematological parameters were compared between infected and healthy fish from the same batch, revealing significantly elevated levels of creatine and ALT (p < 0.05) in the infected group. Histopathological examination revealed severe gill damage, with plasmodia infiltrating and disrupting the lamellar architecture. The well-delineated pink fibrous septa encapsulated mature myxospores and pansporoblasts. Scanning and transmission electron microscopy revealed that the M. koi spores, measuring 5.2 × 2.92 μm, were oval, elongated and pyriform, with coiled polar filaments enclosed within two polar capsules. These findings document the occurrence of M. koi in Thailand, underscore its transboundary transmission via international trade and highlight the need for enhanced biosecurity measures to mitigate the spread of aquatic pathogens.

Poor gill health compromises the health and welfare of farmed Atlantic salmon (Salmo salar) by causing respiratory distress and increased ventilation frequency. Poor gill health is caused by numerous factors, including amoebic gill disease (AGD), jellyfish stings, and toxic algae, and is monitored by fish farmers by manual 'gill scoring'. Gill scoring involves visual inspection of gill surfaces for visible lesions, such as white mucoid patches. In commercial salmon farming, these patches are commonly associated with AGD, a major cause of poor gill health. Manual monitoring of gills is labour-intensive, costly, and stressful for fish. This study tested a non-invasive computer vision approach to detect the association between the gross gill score and fish ventilation rates in commercial farms. We hypothesised that increased ventilation rates of farmed Atlantic salmon were associated with a higher gross gill score. The computer vision model first detected fish heads and classified their mouth states (open or closed) using a convolutional neural network, followed by a tracking-by-detection method to estimate ventilation rates by calculating the frequency with which fish opened and closed their mouths. Ventilation rates were estimated from 240 videos recorded at Tasmanian salmon farms and analysed alongside gross gill score, water temperature, dissolved oxygen, and fish weight. Multiple linear regression analysis revealed a positive association between ventilation rates and gross gill score, although the observed change in ventilation rates was relatively small. As laboratory diagnostic methods did not confirm AGD in this study, the gross gill scores should be interpreted primarily as indicators of gill health, acknowledging that they may also reflect signs consistent with AGD. While the tested computer vision method cannot serve as a diagnostic tool, it may assist the industry in identifying health and welfare issues that require further examination. This approach provides a non-invasive way to oversee health and welfare, enhances management practices, and guides manual health assessments.