Journal of fish diseases最新文献

Life history theory predicts that a trade-off may occur when an increased investment in one fitness component causes a reduced investment in another. Parasites generate changes in the optimal life history traits of organisms, causing compromises for their hosts. The objective of this research was to determine whether trematodes Clinostomum sp. and Uvulifer sp. inflict measurable damage on the males of the viviparous fish Poeciliopsis infans, generating trade-offs between somatic condition and reproductive traits (gonad mass and gonopodium length). We found (i) a negative relationship of large encysted metacercariae and non-encysted metacercariae on somatic condition. Interestingly, individuals with a higher parasite load had a worse body condition, but bigger gonads and longer gonopodium; and, (ii) a bond between small encysted metacercariae and non-encysted metacercariae with smaller gonopodia, only in fish with poorer somatic condition. The strongest correlation was given by the non-encysted metacercariae, probably due to mechanical damage during migration through the body cavity. We did not find any trade-off effects of Uvulifer sp. We consider that the statistical effects found on somatic condition can be attributed to a greater reproductive investment, generating energetic costs that compromise their defences against infection, allowing a greater parasite load.

Real-time PCR (qPCR) testing is an essential component of early detection surveillance systems for Piscirickettsia salmonis infection in Atlantic salmon farms in Chile. Currently, all 11 laboratories in the authorised diagnostic laboratory network use assays based on published protocols. Compared with other P. salmonis qPCR assays, these assays have the advantage of targeting two different genes, that is, the 16S ribosomal gene and the internal transcribed spacer (ITS), potentially allowing for higher diagnostic accuracy. However, variation and lack of harmonisation of qPCR testing systems (e.g., primers/probe, RNA/DNA as target, extraction methods, etc.) may contribute to among-laboratory variation in qPCR results and an increased frequency of false-negative and false-positive results. The purpose of the ring trial reported herein was to compare qPCR results from 11 laboratories in Chile routinely testing Atlantic salmon for P. salmonis as part of a national control program. The panel of 14 samples included duplicates of three concentrations of P. salmonis in a homogenised head kidney, LF89 and EM90 bacteria and two negative controls (blank and a suspension of Flavobacterium psychrophilum). The sample order was randomised across labs, samples were tested blinded and analysed without knowledge of the source lab. Of the laboratories, 8 (72.7%) had at least one incorrect result out of 14 tested samples. Low-concentration samples (C_t of about 30) were more often incorrectly classified by reverse transcription-qPCR (RT-qPCR) (3/6 labs) than by qPCR (0/5). Six (54.5%) labs had at least one false-positive result indicating that cross-contamination was likely during sample processing. Affected laboratories are advised to conduct internal investigations to confirm the causes of false-positive results and recommendations for design and implementation of future ring trials are discussed.

Anisakis simplex larvae, commonly found in marine fish, cause anisakiasis in humans, resulting in gastric to gastro-allergic symptoms. Despite known health risks, the impact of Anisakidae larvae on fish hosts is less understood. This study aimed to investigate this interaction by assessing the feeding strategy of A. simplex. Anisakis larvae were isolated from North Sea Merluccius merluccius tissues (stomach, body cavity, liver and muscle) and were analysed for carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values. Significant differences in δ¹³C values were found among host tissues, with the liver differing from muscle and stomach tissues. In contrast, no differences were noted for the associated parasites. Additionally, δ¹⁵N values indicated that the host occupied a significantly higher relative trophic position than its parasite. This suggests a lack of direct nutrient transfer from host to parasite, as the parasite would typically exhibit higher stable isotope values than the tissue they feed on. Therefore, A. simplex's stable isotope values might reflect those of its previous host (crustacean and/or small fish), providing insights into diet and movement of the paratenic M. merluccius host. Further research is needed to confirm these findings across different fish species and to explore A. simplex as a proxy for trophic ecology.

Fin abnormalities are common in reared fish. They mainly consist of partial to complete lack of rays and severe abnormalities of fin-supporting skeletal elements, which develop during the larval stage, up to the completion of fin skeleton ontogeny. This study reports a new abnormal condition, ray-resorption syndrome (RSS), which developed after the completion of fin ontogeny in initially normal European seabass larvae, leading to extensive loss of fin rays. At 49 days post-fertilisation (dpf) (15 mm standard length, SL) all fish presented normal fins. However, nineteen days later (21 mm SL), significant fin damage, characterised by ray loss or fractures, was observed in all studied populations. The dorsal fin was most affected (55%-84%), followed by the pelvic (27%-53%) and anal fins (7%-17%). Microscopically, multiple non-mineralised areas resembling resorption lacunae were evident along all fin lepidotrichia. By 98 dpf (40 mm SL), the fin-ray loss had advanced, reaching its higher frequency in the dorsal (74%-83%) and caudal fins (71%-94%). Gene expression analysis revealed a significant upregulation of bglap (osteoblast maturation marker), acp5a (osteoclast maturation marker) and mmp13a (extracellular-matrix remodelling marker) in RSS specimens. The results are discussed in respect of the possible causative factors of RSS.

This study describes the identification and characterisation of a new mesophilic Aeromonas salmonicida strain, named HMes1 isolated from Atlantic salmon (Salmo salar L.) in Tasmania. Isolates were identified as Aeromonas salmonicida through phenotypic, phylogenetic and genetic characterisation. After characterisation, the diagnostic phenotypic identification system MicroSys A24 was updated and a new multiplex conventional PCR was developed to enable rapid and inexpensive identification of atypical A. salmonicida, and exclusion of the exotic strain, A. salmonicida ssp. salmonicida.

Understanding the pathogenicity of viral infections in aquatic organisms is vital due to their substantial impact on aquaculture and wild populations. This study assessed the pathogenicity of Callinectes sapidus Reovirus 2 in Callinectes danae and its effects on the metabolic, immunological and behavioural parameters. CsRV2-negative specimens were divided into CsRV2 inoculum (n = 10) and saline injection (n = 15). After 14 days, all the crabs that received the inoculum tested positive for CsRV2. However, 11 crabs from the control group also tested positive and were subsequently considered an additional experimental group. The cumulative mortality in the group challenged reached 70% after 14 days. RT-PCR revealed Callinectes danae Portunibunyavirus 1 presence in CsRV2-injected crabs, explaining heightened mortality. Ammonia flow remained unaffected, but oxygen consumption was significantly impacted (p < 0.05) by CsRV2 and coinfection, suggesting increased metabolic energy expenditure. The coinfection caused an increase in the proportion of crabs with reflex impairment as a likely consequence of physiological exhaustion. Additionally, there was a trend toward reducing the number of granulocytes in coinfected crabs, indicating that granulocytes may be more affected by coinfection. These findings demonstrate the pathogenicity of CsRV2 in C. danae, with coinfection exacerbating metabolic, behavioural and immunological changes, increasing mortality.

Histopathological studies of parasitic infections in fish from the natural environment of Brazilian Amazon, are quite scarce. In this study, we investigated the histopathological changes of the proximal intestine of specimens of the Amazonian fish Hoplias malabaricus infected by the hematophagous nematode Procamallanus (Spirocamallanus) paraensis. The prevalence of the infection was 60%, with an average abundance of 1.46 and an average intensity of 2.43 parasites/fish. No significant difference was observed in the prevalence of infection and fish size or sex, but larger fish showed greater infection intensity, which was also significantly higher in male hosts. Histological sections of the proximal intestine showed reduction and loss of the epithelial lining, exposure of the lamina propria where the nematode interacts with the intestine wall, through the insertion of the buccal capsule and fish cellular debris in the intestinal lumen. In addition, areas with bleeding and inflammatory infiltrate were observed, but no changes or presence of parasite structures were observed in the other tunics of the intestinal wall.

The objective of this study was to evaluate the effect of dietary supplementation with Citrus sinensis (L.) Osbeck essential oil on the growth, immune system, and resistance to Aeromonas hydrophila infection in Colossoma macropomum fingerlings. The experiment was conducted with five treatments (control diet, Tween80 diet, and diets supplemented with 200, 400, and 800 mg L^-1 of C. sinensis essential oil) with four replicates. At the end of the experimental period, growth parameters were measured, and blood samples were collected for thrombogram, leukogram, and phagocytic activity analysis. A bacterial challenge with A. hydrophila was conducted for 96 h. C. macropomum fingerlings that were fed with 400 and 800 mg L^-1 of C. sinensis essential oil had the highest growth parameters, with final weights of 533.18 ± 2.03 mg and 531.91 ± 2.67 mg, respectively, and an increase in the number of thrombocytes, lymphocytes, monocytes, and neutrophils, as well as higher phagocytosis rates compared to the control group. Regarding the challenge, fish in the 400 and 800 mg L^-1 treatments also exhibited the lowest cumulative mortality rate (26.66% ± 3.33%). Therefore, supplementation with C. sinensis essential oil promotes growth, improves health, and enhances resistance to A. hydrophila in C. macropomum fingerlings.

Handfish (Family Brachionichthyidae) is the most threatened marine teleost fish family, however, there is little information on handfish health. We reviewed the results of submissions of mortalities from captive and captive bred spotted handfish (Branchionichthys hirsutus (Lacepède, 1804)) and red handfish (Thymichthys politus (Richardson, 1844)) from a public aquarium from January 2018 to February 2024. Seventeen cases for spotted handfish (comprising 33 individuals) and five cases for red handfish (one individual each) were submitted for mortality investigation. In 2018-2019, six of seven cases were diagnosed with scuticociliatosis. Other conditions included epitheliocystis (1 of 17), infections with metazoan parasites (2 of 17 for spotted handfish and 2 of 5 for red handfish) and hepatic lipidosis (4 of 17). Most submissions were fixed samples for histology with only one fish suitable for microbiology. We recommend development of a coordinated health program for all captive breeders and aquaria, which should include sampling protocols, collection, and preservation in a range of fixatives of all the dying or dead handfish and adapting sublethal sampling, including tank water to assess presence of pathogens and other microorganisms. Risk factors for handfish health in captivity should be assessed. Handfish health database should be established to avoid loss of corporate knowledge in this area.

Mandarin fish ranavirus (MRV) is widely spread in China and causes huge economic losses to the mandarin fish (Siniperca chuatsi) aquaculture. However, the pathogenesis of MRV is still unclear. In the present study, mandarin fish were artificially infected with MRV, and then different gut compartments from diseased fish were subjected to histologic analysis by H&E staining, quantification of proinflammatory genes and MRV copies by qPCR. MRV-MCP protein expression was assessed using indirect fluorescence assay (IFA) and immunohistochemistry. Proliferation of IgM⁺ B cells was evaluated by indirect fluorescence assay (IFA). Then, we found that MRV infection caused serious histologic lesions along with inflammatory cell infiltration, especially in the foregut. A significant accumulation of IgM⁺ B cells was detected in the foregut (~6.5-fold) and hindgut (~3.3-fold), respectively. The expression of inflammation-related genes such as IL-1β, IL-6, IL-8, TNF-α, CSF1r and NCF1 was significantly upregulated in the foregut, varying from ~2.8-fold to ~11.9-fold. In addition, MRV exhibited foregut tropism, according to the investigation of viral loads and MCP protein expression. Overall, our findings indicated that MRV-induced hyperinflammation in the gut eventually led to enteritis. This study provided new insights into uncovering the pathogenesis of MRV infection.