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.

Studies on preventing antimicrobial resistance in aquaculture emphasise the need to responsibly and prudently use antimicrobials, selecting those most effective in controlling and/or reducing mortalities caused by vibriosis. In this study, the distribution of the antimicrobial susceptibility of 28 Vibrio anguillarum isolates from Turkish fish farms was determined using the broth microdilution minimum inhibitory concentration (MIC) test according to the Clinical and Laboratory Standards Institute (CLSI) guideline. The epidemiological cut-off (CO_WT) values of the V. anguillarum isolates of florfenicol (FLO), tetracycline (TET), doxycycline (DOX), oxolinic acid (OXO), enrofloxacin (ENR) and trimethoprim/sulfamethoxazole (SXT) were calculated using the normalised resistance interpretation (NRI) and ECOFFinder methods. Isolates were categorised as belonging to the fully susceptible wild-type (WT) or non-wild-type (NWT) populations. Calculated CO_WT values (in μg mL^-1) were ≤ 1.0 for FLO and DOX, ≤ 0.5 for TET, ≤ 0.016 for ENR, ≤ 0.032 for OXO, and ≤ 4.0 for SXT using the NRI analysis. Percentages of V. anguillarum isolates categorised as belonging to the NWT population were small for the antimicrobials FLO (10.7%) and SXT (0%), whereas they were higher for the antimicrobials OXO (39.3%) and ENR (39.3%). This is the first study to estimate the local CO_WT values for antibiotics used in the control of V. anguillarum isolates recovered from farmed fish in Turkey.

Mannose receptor (MR) is a transmembrane protein and a type of pattern-recognition receptor (PRR) that plays a critical role in the immunity of mammals and fish. In this study, we examined the role of MR in binding with infectious hypodermal and haematopoietic necrosis virus-like particle (IHHN-VLP) and the downstream immune pathway that it triggers in the shrimp Peneaus vannamei. Upon IHHN-VLP challenge, transcripts of MR in P. vannamei (PvMR) increased significantly in all examined tissues, particularly those related to shrimp immunity, including hemocyte, hepatopancreas and gill tissues. Specifically, IHHN-VLP bound to the 34-kDa PvMR protein in shrimp-tissue extracts. Immunohistochemistry results of hemocytes showed that PvMR was initially localised on the plasma membrane but later internalised and dispersed throughout the cytoplasm after IHHN-VLP administration. Binding between IHHN-VLP and PvMR also induced significant upregulation of genes for the antimicrobial peptides (AMPs) penaeidin 3 and crustin, presumably to protect the shrimp against the viral infection. However, knocking down PvMR resulted in down-regulation of all immune-related genes examined. Overall, as an immune-related PRR, PvMR serves as a receptor for invading viruses, which then trigger the expression of AMPs. Strategic designs using PvMR could be developed to either block the interaction of native virus with the host cells or provoke its up-regulation to enhance shrimp immunity, which could open up opportunities to fight against IHHNV infection in shrimp.

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.

Heat stress can increase disease risk in fishes by reducing immune function. Interactions between redband trout (Oncorhynchus mykiss gairdneri) and Flavobacterium columnare, a causative agent of columnaris disease, provide an opportunity to investigate the effects of temperature on immune function and disease resistance during periods of thermal stress. We conducted three trials to characterise differences in immune function and mortality between redband trout held at 18°C and 21°C following challenge with F. columnare. In trial 1, cumulative per cent mortality (CPM) was low and not statistically different between 18°C and 21°C. In trials 2 and 2, we administered higher challenge doses and observed increased CPM overall and significantly greater CPM at 21°C than 18°C. Redband trout upregulated il-8, tnf-α, igm and igt following infection by F. columnare, suggesting that all of these genes may be involved in immune responses to F. columnare infection. We found no differences in the strength of the immune responses between fish held at 21°C versus 18°C. This indicated that 21°C did not elicit sufficient thermal stress to impair immune function and that increased CPM at 21°C versus 18°C was due to enhanced F. columnare virulence.

Thyroid disorders can manifest in several forms, including follicular cell hyperplasia (goitre), follicular cell adenoma and follicular cell carcinoma. Following the detection of large and gradually increasing tumour-like masses in the gular region of wild fourlined terapons (Pelates quadrilineatus) housed in various tanks in a public aquarium in June 2022, September 2022 and October 2023, several fish displaying clinical signs were transported to the Ornamental Fish Clinic at the Faculty of Veterinary Medicine, University of Tehran. Upon clinical inspection, the fish had prominent tumour-like masses in the gular area, located beneath the operculum. Upon histological examination of the first series, the masses revealed thyroid well-differentiated hyperplastic follicles that contained colloid and were lined by cuboidal epithelial cells. There were no signs of cellular atypia or mitotic figures. The study of the second series also revealed the existence of cellular atypia, but still no mitotic figures. In the examination of the third series, apart from the earlier lesions, there was evidence of neoplastic cell invasion into adjacent structures such as the adipose tissue and subepithelial layer. In addition, there was moderate cellular pleomorphism and a limited number of mitotic figures. Although the termination of water ozonation and the addition of potassium iodide to the feed were effective in treating thyroid hyperplasia, the treatment for thyroid neoplasia was not successful. The present study provides the evidence of clinical and histopathological findings of follicular cell hyperplasia, adenoma and adenocarcinoma of the thyroid gland in fourlined terapon.

This study assesses the health status of the edible Tehuelche scallop, Aequipecten tehuelchus, reporting the epidemiological results of the parasites and their infection levels by histopathological analysis and transmission electron microscopy. Environmental factors (site: West and East domains of the San José gulf, seawater temperature) and host traits (size, physiological condition index, gonad development stages) associated with parasite load (prevalence, mean intensity, parasite abundance and total parasite abundance) were tested with generalised linear models (GLMs). Histopathological results revealed Rickettsia-like organisms (RLOs), several protozoans (Trichodina sp., Nematopsis sp. and APXSc apicomplexans) and metazoans (turbellarians and Tumidotheres maculatus pea crabs) as well as inflammatory lesions in form of granulomas and hemocytic infiltration. The prevalence of the parasitofauna did not vary significantly between gulf domains, except the apicomplexan APXSc that was significantly most prevalent in scallops from the East Domain. However, the mean intensity of infection seemed to be determined by the gulf domains, which present distinct hydrographic regimes, where RLO's, Trichodina sp. and T. maculatus were significantly more intense in scallops from the West, opposite with Nematopsis sp. infection. Total parasite abundance was influenced by seasonal variations, it was negatively correlated with warmer temperatures. The physiological condition index of A. tehuelchus seemed not to be affected by the presence or abundance of any of the parasites. Nevertheless, the apicomplexan APXSc would represent a significant risk to the health of A. tehuelchus due to the pathological conditions, and surveillance of this parasite is needed for a sustainable A. tehuelchus fishery.

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.

The classic epidemiological triangle model of host-environment-pathogen is recently being reshaped into a tetrahedron, with the growing understanding of the importance of the microbiome in this array. The gills, being a gateway into the fish body, bearing an important role in fish homeostasis, host a complex microbiome that reflects the ambient water, while also showing resemblance to gut microbiome. Next-generation sequencing (NGS) and improvements in data analysis tools enable researchers to gather and analyse a lot more data than ever before, take a closer, more detailed look at microbiota, and gain a much better understanding of the biological processes at work in these complex relations. Here, 16S rRNA amplicons of bacterial DNA extracted from the gills of 36 asymptomatic specimens of three wild fish species from the South China Sea (Nemipterus japonicus, Alepes djebaba, and Saurida tumbil) were sequenced using NGS. Data analyses revealed the presence of 20 potentially pathogenic species, including several zoonotic agents. Gill microbiota exhibited host species-specificity, and expressed a significant difference between demersal and pelagic-amphidromous fish. It is suggested that this method be more widely implemented, in order to gain more insight on ocean ecosystems' health status, as well as fish stocks of commercial importance.

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.