Journal of fish diseases最新文献

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.

This case report presents a recent case of scuticociliatosis in a whitetip reef shark (Triaenodon obesus), housed at a zoo (Haus des Meeres Aqua Terra Zoo, Vienna, Austria). Clinical signs such as uncoordinated swimming and body tilt were observed prior to death. Postmortem examination and magnetic resonance imaging (MRI) revealed significant brain lesions consistent with granulomatous or necrotising encephalitis. Histopathology and molecular diagnostics confirmed the presence of the scuticociliate Miamiensis avidus and/or Philasterides dicentrarchi in the brain, with extensive tissue invasion. This case underscores the pathogenicity of scuticociliates in elasmobranchs, highlighting the need for effective management practices in aquaria to prevent or mitigate such infections. In this study, we present the first documented infection with scuticociliates in the whitetip reef shark.

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.

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.

Piscirickettsiosis is a systemic infectious disease caused by Piscirickettsia salmonis, a Gram-negative, biofilm-forming bacterium capable of infecting the main salmonid species farmed in Chile. The initial stages of P. salmonis infection occur in the mucous membranes of the skin, gills, and intestine before spreading systemically. At the intestinal level, several pathogenic bacteria can disrupt the functionality of the epithelial barrier as an infection mechanism, associated with alterations in the expression of immune genes and intercellular junctions. The aim of this study was to determine in vitro the effect of P. salmonis infection in both sessile and planktonic conditions on the morpho functionality of the intestinal epithelial cell line RTgutGC of rainbow trout. Thus, the effect of P. salmonis infection on immune gene expression and intercellular junctions was evaluated using RT-qPCR, intercellular junction protein levels via Western blot, transepithelial resistance (TEER) modulation, cytotoxicity, and ZO-1 localization through immunofluorescence. The results indicate that P. salmonis LF-89 and EM-90 in both sessile and planktonic conditions significantly modulate the expression of il-8, il-1β, tgf-β, and zo-1, claudin-3, and E-cadherin. Interestingly, alterations in the levels of Claudin-3 and E-cadherin, associated with the altered immunolocalization of ZO-1 after the infection with P. salmonis, were detected. Importantly, an increase in bacterial translocation associated with a decrease in the TEER value, from the first 12 h post-infection, was measured. These findings suggest that P. salmonis modulates the expression of genes and proteins related to intercellular junctions, modifying the epithelial morpho-functionality, which could allow bacterial translocation in the early stages of infection.

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.

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.

Lactococcus petauri is an emerging bacterial pathogen associated with disease outbreaks in freshwater and marine fish species worldwide. While it has been increasingly reported in countries bordering the Mediterranean Sea, no official records of L. petauri have yet been made in Italy for saltwater species. This study reports, for the first time, the presence of L. petauri in European seabass (Dicentrarchus labrax) farmed in land-based tanks along the south-western coast of Italy, based on a retrospective analysis of previously isolated strains. Although only a single isolate was positive, the finding is of notable significance as it originated from a sample collected in 2012. This temporal aspect highlights the likelihood that L. petauri has been circulating in Italian aquaculture systems for at least a decade. The isolate also exhibited a broad antimicrobial resistance profile, including resistance to amoxicillin, fluoroquinolones and trimethoprim/sulfamethoxazole. The historical misidentification of L. petauri is linked to its clinical similarity with Lactococcus garvieae. This highlights the value of re-analysing archived strains with modern tools and underlines the need for accurate diagnostics in aquaculture. The detection in D. labrax extends the known host range and suggests a longer, undetected presence in the Mediterranean.

Freshwater is a non-pharmaceutical tool used for the control of Caligus infestation with a proven effect on adult and larval stages. However, the minimum exposure time to achieve a greater effect (100%) on juvenile stages has not been determined through in vivo tests. Therefore, it is important to determine these minimum times on C. rogercresseyi chalimus, considering that freshwater baths should be performed with a wellboat to achieve the greatest effect. A study was thus formulated that allowed us to evaluate the effect of applying freshwater treatment on C. rogercresseyi juveniles at different exposure times through in vivo tests on Atlantic salmon (Salmo salar). The results indicated that a treatment of more than 2.5 h with freshwater induces a greater effect (100%) and mortality (~95%) on juvenile stages, at least at chalimus III-IV. Juvenile stages are a critical point in population dynamics and control of the parasite, since those that survive treatment increase the possibility of augments in parasitic loads in the short term, and cause loss of sensitivity. Based on these results, freshwater treatment exposure time should exceed 2.5 h in order to ensure effectiveness on parasite stages and, therefore, to avoid development of resistance to freshwater and prolong the useful life of this non-pharmaceutical tool.

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.