Journal of fish diseases最新文献

Spiroplasma eriocheiris is a pathogen in the Chinese mitten crab Eriocheir sinensis and is associated with tremor disease. S. eriocheiris infects virtually all artificially bred crustaceans, resulting in significant economic losses to the aquaculture industry in China. Recombinase polymerase amplification (RPA) is considered a promising technology for the rapid and sensitive detection of disease. For the rapid detection of S. eriocheiris, this study established basic RPA, RPA-EXO and RPA-LFD, which were visualised via agarose gel electrophoresis, SYBR Green I, fluorescence signals and test lines on lateral flow dipsticks. Specific primers and probes were designed based on the 16S ribosomal RNA sequence of S. eriocheiris. The optimal primer pairs for the basic RPA, RPA-EXO and RPA-LFD were RPA-F3/R3, RPA-F3/R3 and RPA-LFD-F3/R3, respectively. The optimal temperatures and times of basic RPA, RPA-EXO and RPA-LFD were 37°C for 25 min, 39°C for 30 min and 39°C for 10 min, respectively. The specificity test indicated that in addition to the positive test results for S. eriocheiris, the other five DNA templates tested negative, demonstrating strong specificity. The results of the sensitivity test revealed that the detection limits of RPA, RPA-EXO and RPA-LFD were 5.77 × 10⁻², 5.77 × 10⁻⁴ and 1.52 × 10⁻⁶ ng/μL, respectively, indicating high sensitivity. This study established three methods for the detection of S. eriocheiris that are characterised by a constant temperature, rapid response, high sensitivity and strong specificity.

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.

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.

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.