Author: marina02

White grape marc extracts as potential modulators of fish growth, immune status and disease resistance

The intensification of aquaculture increases the vulnerability of farmed fish to infectious diseases. While antibiotics help manage these diseases effectively, their use raises environmental concerns and affects public perception of aquaculture. Moreover, the overuse of antibiotics promotes antimicrobial resistance (AMR) in pathogens, prompting strict regulations. In many countries, the preventive use of antibiotics is prohibited. Consequently, developing efficient and sustainable alternatives to antibiotics is an urgent need of the aquaculture sector. White grape marc extracts are rich in polyphenols, with antimicrobial and antioxidant capacity, and are an interesting alternative to replace conventional antibiotics. In this work, we assessed the potential of three white grape marc extracts (obtained with an alcohol -A, a glycol -G, and a ketone – K) asmodulators of European seabass (Dicentrarchus labrax) growth, immune status, and disease resistance. We first evaluated the extracts’ antimicrobial activity against several important aquaculture bacterial pathogens. A and G grape marc extracts inhibited the growth ofVibrio vulnificus,V. harveyi,Tenacibaculum maritimum,andPhotobacterium damselaesubps.piscicida, while K inhibitedV. harveyiandT. maritimum. The three grape marc extracts were then used to prepare European seabass diets containing each extract (A, G, and K) incorporated at 450ppm of polyphenols (based on previousin vivo trials used to determine the ideal extract dose).Triplicated groups of European seabass juveniles were fed each diet for 42 days and compared toa control group fed a control diet(CTR) without extract supplementation.There were no differences between dietary treatments in all growth parameters assessed, namely final body weight, weight gain, daily growth index, feed intake and feed efficiency. Fish fed the G diet had the highest absolute values of superoxide dismutase, glutathione reductase and glutathione peroxidase activities.The feeding trial was followed by a bacterial-challenge trialwith V. harveyi, or with PBS (non-challenged fish; negative control). Challenged fish had a mortality rate between 67% to 83%, while non-challenged fish (PBS) had 100% survival. Although there were no significant differences in all dietary groups when compared to the control, fish fed G and K diets managed to resist better to the infectionwith V. harveyi, having higher survival rates. Grape mark extracts are potential alternatives to antibiotics in aquaculture.This work was funded by the European Union´s Horizon 2020 Research and Innovation program under grant agreement No 101036768 – NeoGiANT.

1. SERRA, CLAUDIA, CIIMAR-UP, Presenter
2. MAGALHAES, RUI, CIIMAR-UP, Author
3. CASTRO, MIGUEL, CIIMAR-UP, Author
4. SANTOS, RAFAELA, CIIMAR-UP, Author
5. ENES, PAULA, CIIMAR-UP, Author
6. BERMUDEZ, ROBERTO, USC, Author
7. AZEVEDO, ANA, USC, Author
8. PÉREZ-DÍAZ, MARTIN, USC, Author
9. QUIROGA, MARIA ISABEL, USC, Author
10. CELEIRO, MARIA, LIDSA, Author
11. LORES, MARTA, USC, LIDSA, Author
12. COUTO, ANA, CIIMAR-UP, Author
13. OLIVA-TELES, AIRES, CIIMAR-UP, Author

Designing nanoformulations for the delivery of peptidase-sensitive antimicrobial against fish bacterial infections

Introduction: Anisaxin-2S (A-2S) is a cecropin antimicrobial peptide (AMP) isolated from the zoonotic nematodes Anisakis simplex and A. pegreffii. While it has shown high potency against Gram-negative bacteria from both marine and terrestrial environments, including the multidrug resistant strains, a preliminary pharmacokinetic study in mice has shown low retention time of the peptide in host serum. The latter is due to A-2S sensitivity to blood peptidases, hindering the availability of the peptide for the interaction with bacteria.

Methodology: To improve the stability of parenterally applied A-2S to be used as antibacterial treatment in aquaculture, we designed organic polymer nanocapsules

aiming to protect A-2S within the host circulation and deliver a concentration sufficient to kill bacteria. Physical properties of the nanocapsules were tested, as well as the effect of formulation in vitro cell assay.

Results: The formulation consisted of a water in oil in water (WOW) emulsion, subsequently enveloped with chitosan to facilitate the attachment to the negatively charged bacteria cell wall. A-2S-filled nanocapsules, measuring 180 nm on average, showed a dose- and time-dependent cytotoxic activity in human peripheral blood cells (HPBCs), but statistically significant only at the highest concentrations tested (>2.8 µg/ ml), after prolonged treatment (24-48 h). In contrast, the formulation did not induce DNA strand breaks in HPBCs, suggesting no genotoxicity. The release profile of the A-2S from nanocapsules showed that the maximum concentration (2.49 ng/ µl) was released between 8-12 h.

Conclusion: The calculated maximum concentration of released A-2S, equalling 0.72 µM is just above the minimum inhibitory concentration for the majority of Mediterranean Vibrio spp. and Aeromonas spp. we tested. While the proof of concept has been confirmed, the next step is to develop an optimised formulation with a higher initial concentration of A-2Sto be released over 24 h.

Funding: Funded by the European Union under the Horizon Europe Programme, Grant Agreement No. 101084204 (Cure4Aqua) and Grant Agreement No. 101084651 (IGNITION), UK Research and Innovation, Swiss Confederation and Federal Department of Economic Affairs, Education and Research EAER, and State Secretariat for Education Research and Innovation SERI. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Executive Agency (REA). Neither the European Union nor the granting authority can be held responsible for them.

1. MLADINEO, IVONA, IMAS, UNIVERSITY OF TASMANIA, Presenter
2. Arakelyan, Anush, BCAS PARU, Author
3. Yostawonkul, Jakarwan, National Nanotechnology Centre, Author
4. Gajski, Goran, IMI, Author
5. Yata, Teerapong, Chulalongkorn University, Author
6. Mandalakis, Manolis, HCMR, Author
7. Katharios, Pantelis, HCMR, Author
8. Pirarat, Nopadon, Chulalongkorn University, Author
9. Rodkhum, Channarong, Chulalongkorn University, Author

Monitoring of Tetracapsuloides bryosalmonae via eDNA: influencing environmental factors

Tetracapsuloides bryosalmonae is the causative agent of Proliferative Kidney Disease (PKD), a temperature dependent disease in salmonids. The disease affects farmed and wild salmonid populations in the northern hemisphere, in Switzerland particularly wild brown trout (Salmo trutta). PKD was discussed as one contributing factor to brown trout population decline in Switzerland. Therefore, the disease is reportable and monitoring is recommended. Currently, monitoring methods for PKD are invasive, requiring the euthanization of young brown trout, which further exacerbates pressure on already vulnerable populations. Non-invasive environmental DNA (eDNA)-based protocols have been successfully developed for the detection and monitoring of various species, including T. bryosalmonae (Stelzer et al., 2024). However, there is limited understanding of how environmental factors might influence the detection of the pathogen.

This study aimed to identify environmental parameters, such as season, water and air temperature, and precipitation, that may affect the detection of T. bryosalmonae, in order to determine the optimal sampling period. Water samples from six PKD-positive rivers in the Swiss Midlands were collected over a full year and analyzed for the presence of T. bryosalmonae DNA using droplet digital PCR (ddPCR). Additionally, the infection status of bryozoa, the final host for T. bryosalmonae, was assessed from the study rivers. Water temperature was continuously monitored using temperature loggers at each sampling site, and data on precipitation and air temperature were also collected.

We found T. bryosalmonae DNA in all rivers by ddPCR. Positive results were almost exclusively retrieved between late spring and early autumn (mid-April until end of October). Furthermore, 98.3 % of T. bryosalmonae positive water samples were collected in average daily water temperatures above 8°C and 71.9% of the positive samples even above 14°Csuggesting that water temperature plays a significant role in the presence of the parasite’s eDNA. Precipitation also posed challenges by causing filter clogging, which negatively impacted the sampling process.

These findings provide a foundation for future recommendations regarding the eDNA-based monitoring of T. bryosalmonae, offering insights into the optimal timing and environmental conditions for effective detection.

1. Schmidt-Posthaus, Heike, Institute for Fish and Wildlife Health, University of Bern, Presenter
2. Stelzer, Moritz, Institute for Fish and Wildlife Health, Author
3. Delalay, Gary, Institute for Fish and Wildlife Health, Author

Is proliferative kidney disease serious problem in the rivers of the Czech Republic?

Miroslava Palíková^1,2, Ľubomír Pojezdal³, Hana Novotná^1,2,3, Jitka Motlová³, Ivana Mikulíková^1,2, Ivana Papežíková^1,2, Ivona Toulová^1,2

¹University of Veterinary Sciences Brno; ²Mendel University in Brno; ³Veterinary Research Institute; Czech Republic

Introduction: Proliferative kidney disease (PKD) affects both wild and farmed salmonid fish, causes losses in aquaculture and a substantial decline in brown trout populations throughout Europe. The life cycle of Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea) involves freshwater bryozoans as invertebrate hosts. The kidney represents the main target organ in fish. In the lumen of the kidney tubules, T. bryosalmonae forms sporogonic developmental stages and can be detected in this organ with the use of molecular methods. With climate change, more PKD cases are to be anticipated, as the life cycle of parasite is highly temperature-dependent. The aim of this study was to evaluate the prevalence of T. bryosalmonae in wild brown trout (Salmo trutta) populations in the rivers of the Czech Republic.

Methodology: Rivers of three basins (Elbe, Morava and Oder) were investigated, and in total, 525 fish from 52 locations from 36 streams were sampled. Where possible, at least ten fish per location were caught by electrofishing. At the same time, hatchery fish from 13 main hatchery fish producers in the Czech Republic were examined. The animals were euthanised, measurements were taken and the pathoanatomical and parasitological examinations (including collection and taxonomic determination of parasites from the skin, fins and gills by light microscopy) were conducted on-site. Tissue samples from each individual were collected and stored in 70% ethanol for PKD examination (caudal kidney) and virological examination (cranial kidney, spleen and heart) using molecular methods. Ethanol-stored samples of the caudal kidney were examined by real-time PCR for the presence of T. bryosalmonae. The fish were also examined for the presence of salmonid viruses (VHS, IHN, PRV-3, and IPN).

Results: Swelling of the caudal kidney, indicative of the presence of T. bryosalmonae, was found in 37 specimens from rivers. Only 13 locations from 52 were PCR negative, it means T. bryosalmonae was present in 75 % of examined locations. On the other hand, VHSV, IHNV and INPV were not detected in any location and PRV-3 was detected in two locations (Odra basin) only.

Conclusions: High prevalence of PKD in wild brown trout in the Czech Republic was revealed.

Acknowledgements: This research was supported by the University of Veterinary Sciences Brno (FVHE/Pikula/2025ITA22) and by the Ministry of Agriculture of the Czech Republic (project QK23020064).

1. PALIKOVA, Miroslava, 1University of Veterinary Sciences Brno, Czech Republic; 2Mendel University in Brno, Czech Republic;, Presenter
2. POJEZDAL, Ľubomír, 3Veterinary Research Institute, Czech Republic, Author
3. NOVOTNÁ, Hana, 1University of Veterinary Sciences Brno, Czech Republic; 2Mendel University in Brno, Czech Republic; 3Veterinary Research Instit, Author
4. MOTLOVÁ, Jitka, 3Veterinary Research Institute, Czech Republic, Author
5. MIKULÍKOVÁ, Ivana, 1University of Veterinary Sciences Brno, Czech Republic; 2Mendel University in Brno, Czech Republic;, Author
6. PAPEŽÍKOVÁ, Ivana, 1University of Veterinary Sciences Brno, Czech Republic; 2Mendel University in Brno, Czech Republic;, Author
7. TOULOVÁ, Ivona, 1University of Veterinary Sciences Brno, Czech Republic; 2Mendel University in Brno, Czech Republic;, Author

Amazonian Freshwater Ellipsomyxa (Cnidaria: Myxozoa): Insights into Taxonomy, Phylogeny, Host Specificity, and Ultrastructure

Introduction

The genus Ellipsomyxa was originally established to accommodate the marine species Ellipsomyxa gobii, followed by the description of several additional species infecting the gallbladders of marine and brackish water fish. Since 2018, however, a growing diversity of Ellipsomyxa species has been reported from South American freshwater fish. This study presents new data on Amazonian Ellipsomyxa spp., providing insights into their taxonomy, phylogeny, host specificity, and ultrastructure.

Methodology

Between October 2021 and January 2023, 26 specimens of Hypophthalmus marginatus; three of Pinirampus pirinampu; and 11 of Platynematichthys notatus – all siluriform fish of the family Pimelodidae – were collected, along with 104 specimens of Curimata inornata (Characiformes: Curimatidae) and seven of Prochilodus nigricans (Characiformes: Prochilodontidae), at the confluence of the Tapajós and Amazon Rivers, in Santarém, Pará State, Brazil. Bile samples from fish infected with myxosporeans of the genus Ellipsomyxa were immediately fixed in 100% ethanol for small subunit ribosomal DNA (SSU rDNA) sequencing and subsequent phylogenetic analyses using Bayesian Inference and Maximum Likelihood. Additional samples were preserved in 2.5% glutaraldehyde for morphological and ultrastructural studies.

Results

Two previously undescribed species of Ellipsomyxa were identified: one infecting the gallbladder of H. marginatus, and the other infecting the gallbladder of C. inornata. Ellipsomyxa amazonensis, originally described in the pimelodid Brachyplatystoma rousseauxii, had its host range expanded to include two additional pimelodid species – P. pirinampu and P. notatus. The species Ellipsomyxa santarenensis, described from the cichliform Satanoperca jurupari, had its taxonomy revised and is here considered a junior synonym of Ellipsomyxa paraensis, originally described from Cichla monoculus. This species is now also reported in two new hosts: S. jurupari and the characiform P. nigricans.

Conclusion

Ellipsomyxa paraensis, E. amazonensis, and E. arariensis were able to infect more than one host species. Notably, E. paraensis and E. arariensis infected hosts from different orders and families, indicating that, at least in the Amazon freshwater environment, Ellipsomyxa species exhibit low host specificity.

Funded by São Paulo Research Foundation – FAPESP (Thematic Project #2018/24980-8; Doctoral Fellowship #2023/06420-3).

1. ADRIANO, EDSON, INSTITUTO DE CIÊNCIAS AMBIENTAIS, QUÍMICAS E FARMACÊUTICAS, UNIVERSIDADE FEDERAL DE SÃO PAULO-UNIFESP, Presenter
2. Figueredo, Rayline, Instituto de Biologia, Universidade Estadual de São Paulo, Author
3. Müller, Maria I, Oregon State University, Author
4. Corrêa, Lincoln, Universidade Federal do Oeste do Pará, Author
5. Okamura, Beth, Natural History Museum-London, Author
6. Long, Paul, King’s college London, Author

In-Silico Investigation of Fungal Sequences in Myxozoan and Cnidarian Genomes: Evidence of Horizontal Gene Transfer and Evolutionary Implications

Introduction

Horizontal gene transfer (HGT) is increasingly recognized as a significant driver of evolutionary innovation across diverse taxa, including eukaryotes. Notably, fungal sequences detected within the genomes of myxozoans, specialized metazoan parasites within Cnidaria, suggest complex evolutionary interactions between these organisms. This study systematically investigates fungal-derived genes within myxozoan genomes, examining potential transfer mechanisms, evolutionary implications, and functional significance, providing insights relevant to parasite-host interactions and adaptive metabolic strategies.

Materials and Methods

Genome assemblies for multiple myxozoan species were retrieved from the GenBank database, and fungal genomes from extensive GenBank datasets were employed to identify homologous sequences via BLAST searches. Comparative genomics and phylogenetic analyses (maximum likelihood and Bayesian inference) were performed using MEGA and MrBayes to assess phylogenetic incongruence indicative of HGT. Alien Index calculations and genomic context analyses (codon usage bias, GC content, association with mobile elements) supported candidate validation. Functional annotations, structural modeling, and interaction network analyses provided deeper insights into gene functionality.

Results

Multiple fungal-origin genes were confirmed in myxozoan genomes, including carbohydrate-active enzymes, 6-phosphofructokinase, aquaporins, and ABC transporter ATP-binding proteins, implicating diverse metabolic and physiological roles. Transfer mechanisms identified included HGT mediated by environmental uptake and symbiotic interactions. Structural modeling and network analyses indicated functional integration and potential evolutionary advantages in metabolic adaptation and host-parasite interactions. These findings underscore the extensive role of fungal genetic material in myxozoan evolution, highlighting intricate evolutionary dynamics facilitated by horizontal gene transfers.

Conclusion

Through horizontal gene transfer (HGT), fungal-origin genes in myxozoan genomes appear to play a significant evolutionary role.

Funded by São Paulo Research Foundation – FAPESP (Thematic Project #2018/24980-8; Postdoctoral fellowship # 2023/12298-6 – A.G.A. Ibrahim).

1. ADRIANO, EDSON, INSTITUTO DE CIÊNCIAS AMBIENTAIS, QUÍMICAS E FARMACÊUTICAS, UNIVERSIDADE FEDERAL DE SÃO PAULO-UNIFESP, Author
2. Ibrahim, Amr, INSTITUTO DE CIÊNCIAS AMBIENTAIS, QUÍMICAS E FARMACÊUTICAS, UNIVERSIDADE FEDERAL DE SÃO PAULO-UNIFESP, Presenter

Chloromyxum dasyatidis (Myxosporea: Chloromyxidae) a parasite of the common stingray Dasyatis pastinaca (L.) from Tunisian waters

The present study, aims to describe a new marine coelozoic Chloromyxum species, based on morphological, ultrastructural, and molecular features. Phylogenetic analyses were performed for analysing the relationship of the new species with the existing marine Chloromyxum spp. from different hosts and continents. In addition, seasonal variation and the effect of host size on the prevalence of infection were evaluated.

The new species Chloromyxum dasyatidis is described from the gallbladder of the elasmobranch fish Dasyatis pastinaca (Linnaeus) from the Mediterranean coast off Tunisia. Plasmodia were polysporic (containing up to 30 myxospores) floating free in the bile. Mature myxospores were subspherical measuring 13.0 ± 0.3 (12.5–13.9) µm in length, 11.3 ± 0.5 (10.2–12.2) µm in width, and 11.8 ± 0.5(11.4–12.7) µm in thickness. The four polar capsules were pyriform measuring 4.4 ± 0.3 (4.0–4.9) µm long and 3.5 ± 0.3 (3.0–3.8) µm wide. Valves were ornamented by 5 to 7 elevated surface ridges and displayed short caudal filaments.

Phylogenetically, this species grouped within the Chloromyxum sensu stricto lineage, forming a small clade together with the genetically more similar species C. acuminatum (Lisnerová et al., 2022) infecting Rhinoptera jayakari in South Africa with 95.4% similarity, and C. myolibati (Gleeson & Adlard, 2012) infecting Myliobatis australis in Tasmania with 95% similarity.

Prevalence of infection of C. dasyatidis displayed notable seasonal fluctuation. C. dasyatidis had an overall prevalence of infection of 38.5%, with highest values recorded during autumn (70.8%), followed by summer (60.0%), spring (16%), and winter (4.5%).

The prevalence of infection of C. dasyatidis showed a slight variation in relation to host size. The comparison between the disc width size classes showed that the highest prevalence of infection 48.1% (13/27) was observed in the 28–33 cm size class, followed by the prevalence of infection 41.2% (14/34) recorded in the 34–39 cm size class, then 35.0% (7/20) recorded in the 40–45 cm size class, while the lowest rate of infection 20.0% (3/15) recorded from larger fish (46–51 cm). Nevertheless, no significant relathionship was found between host size and prevalence rates of C. dasyatidis (χ2 = 3.4, df=3, P>0.05).

1. BAHRI, Sihem, UNIVERSITY OF TUNIS EL MANAR, FACULTY OF SCIENCES OF TUNIS, Presenter
2. ELLOUMI, Amira, UNIVERSITY OF TUNIS EL MANAR, FACULTY OF SCIENCES OF TUNIS, Author
3. RANGEL, Luis F., CIIMAR, University of Porto, Matosinhos, Portugal, Author
4. QUILICHINI, Yann, University of Corsica Pascal Paoli, Corte, France, Author
5. SANTOS, Maria J., CIIMAR, University of Porto, Matosinhos, Portugal, Author

In-Silico Investigation of Fungal Sequences in Myxozoan and Cnidarian Genomes: Evidence of Horizontal Gene Transfer and Evolutionary Implications

Introduction: Horizontal gene transfer (HGT) is increasingly recognized as a significant driver of evolutionary innovation across diverse taxa, including eukaryotes. Notably, fungal sequences detected within the genomes of myxozoans, specialized metazoan parasites within Cnidaria, suggest complex evolutionary interactions between these organisms. This study systematically investigates fungal-derived genes within myxozoan genomes, examining potential transfer mechanisms, evolutionary implications, and functional significance, providing insights relevant to parasite-host interactions and adaptive metabolic strategies. Materials and Methods: Genome assemblies for multiple myxozoan species were retrieved from the GenBank database, and fungal genomes from extensive GenBank datasets were employed to identify homologous sequences via BLAST searches. Comparative genomics and phylogenetic analyses (maximum likelihood and Bayesian inference) were performed using MEGA and MrBayes to assess phylogenetic incongruence indicative of HGT. Alien Index calculations and genomic context analyses (codon usage bias, GC content, association with mobile elements) supported candidate validation. Functional annotations, structural modeling, and interaction network analyses provided deeper insights into gene functionality. Results: Multiple fungal-origin genes were confirmed in myxozoan genomes, including carbohydrate-active enzymes, 6-phosphofructokinase, aquaporins, and ABC transporter ATP-binding proteins, implicating diverse metabolic and physiological roles. Transfer mechanisms identified included HGT mediated by environmental uptake and symbiotic interactions. Structural modeling and network analyses indicated functional integration and potential evolutionary advantages in metabolic adaptation and host-parasite interactions. These findings underscore the extensive role of fungal genetic material in myxozoan evolution, highlighting intricate evolutionary dynamics facilitated by horizontal gene transfers. Conclusion: Through horizontal gene transfer (HGT), fungal-origin genes in myxozoan genomes appear to play a significant evolutionary role.

1. IBRAHIM, AMR, UNIVERSIDADE FEDERAL DE SÃO PAULO, Presenter
2. Adriano, Edson, UNIVERSIDADE FEDERAL DE SÃO PAULO, Author

Myxozoans detected in the gallbladders of farmed marine fishes in Japan

A disease characterized by emaciation has recently been reported in farmed greater amberjack (Seriola dumerili) in western Japan. Although the causative agent remains unidentified, myxospores of the genus Ceratomyxa have been frequently found in the gallbladders of affected fish. In Japan, only three species of gallbladder-infecting myxozoans have been reported from farmed marine fish to date, all in Seriola quinqueradiata. This study aimed to survey myxozoans in the gallbladders of various farmed marine fish in Japan.

The gallbladders of more than 200 individuals from 17 farmed marine fish species, spanning eight families including Carangidae, Oplegnathidae, Serranidae, Scombridae, Sparidae, Tetraodonidae, Monacathidae and Paralichthyidae, were examined for the myxozoan infection. Most of the fish were juveniles produced in hatcheries and reared in sea cages. When spores and/or development stages were observed in bile, parasites were identified based on morphology and molecular characteristics.

At least 16 distinct myxozoan species were observed in 11 different fish species. Among them, three species Myxobolus spirosulcatus, Ceratomyxa buri, and Ceratomyxa barnesi were identified. The other 13 species were not identified to the species level and are potentially undescribed. Out of 16 detected species, 12 species belonged to Ceratomyxa. Infection prevalence was high among amberjacks: more than 70% in S. dumerili, S. quinqueradiata and yellowtail amberjack (Seriola aureovittata). Mixed infections involving Ceratomyxa and Myxobolus were found in S. dumerili and red seabream (Pagrus major).

The infection cycles of these parasites are likely maintained within aquaculture sites. No apparent abnormalities were observed in the gallbladders or livers of fish host, and the presence of myxozoans was not consistently associated with emaciation or other clinical signs. Nevertheless, environmental and stress-related factors may enhance their impact to the fish host. Further pathological studies are needed in the future to better understand their potential role in fish health and effects on aquaculture. This study contributes to the understanding of myxozoan diversity in Japanese fauna.

1. Oe, Reika, Aquaculture Research Institute, Kindai University, Presenter
2. Chỉnh, Nguyễn Ngọc, Institute of Biology, Viet Nam Academy of Science and Technology, Author
3. Ishitani, Hiroe, Aquaculture Research Institute, Kindai University, Author
4. Yoshii, Keisuke, Fisheries Research Division, Oita Prefectural Agriculture, Forestry and Fisheries Research Center, Author
5. Shirakashi, Sho, Aquaculture Research Institute, Kindai University, Author

Characterization and host-parasite interactions of Myxobolus n. sp. (Cnidaria: Myxozoa) infecting the gills of a Brazilian bryconid

Myxozoa are a highly diverse group of endoparasitic cnidarians, comprising approximately 2,600 species that infect various tissues and organs of vertebrates, primarily fish. These parasites affect economically important fish species in aquaculture and commercial fishing, such as Salminus brasiliensis (Cuvier, 1816), known as dourado, a carnivorous fish of significant economic importance in Brazil. This study aimed to describe Myxobolus n. sp. infecting S. brasiliensis in the Pantanal region of Brazil through morphological and molecular analyses (SSU rDNA sequencing) and to characterize the host-parasite interaction using histopathological analysis. Specimens were collected from the Miranda River, Mato Grosso do Sul, where eleven S. brasiliensis individuals were sampled, and seven (63.6%) were found to be parasitized. Myxobolus n. sp. was observed in the gill filaments, forming white and elongated plasmodia measuring 2.1 ± 0.5 mm in length. Morphological analysis under light microscopy revealed mature myxospores, pear-shaped in frontal view, measuring 10.1 ± 0.3 μm in length, 6.6 ± 0.2 μm in width, and 5.1 ± 0.2 μm in thickness. In the lateral view, the myxospores were biconvex with symmetrical valves. The polar capsules were elongated, asymmetrical, and occupied more than half of the spore body, measuring 4.9 ± 0.3 μm in length and 1.9 ± 0.2 μm in width. Molecular analysis based on SSU rDNA yielded a 1,954 bp fragment. BLASTn analysis identified Myxobolus filamentum, previously described infecting Brycon orthotaenia from the São Francisco River in Minas Gerais, Brazil, as the closest species, with 95.3% similarity. Histopathological analysis using hematoxylin and eosin staining revealed numerous plasmodia of Myxobolus n. sp. developing within the subepithelial connective tissue of the distal region of the gill filaments. The parasitic development caused compression of adjacent blood vessels, indicating structural disruption of the gill tissue. A layer of fibroblasts was observed surrounding the plasmodia, along with granulocytes in the connective tissue, suggesting an active host immune response to the infection. These findings demonstrate the pathological alterations associated with Myxobolus sp. infection and its potential impact on gill function. Myxobolus n. sp. is the sixth myxozoan species described in S. brasiliensis, and the results based on morphological, molecular, and histopathological analyses contribute to understanding how this new species interacts with its host.

Acknowledgments: This work was supported by the  Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) through a doctoral fellowship to C. M. Meira (grant #2023/15107-7), a Thematic Project (grant #2018/24980-8), and PIPE grants (Innovative Research in Small Business Program) to T. Milanin (grants #2024/01323-2 and #2023/12685-0).

1. MEIRA, CAROLINE MUNHOZ, UNIVERSIDADE DE SÃO PAULO – USP, Author
2. MILANIN, TIAGO, UNIVERSIDADE DE SÃO PAULO – USP, Presenter
3. ADRIANO, EDSON APARECIDO, UNIVERSIDADE FEDERAL DE SÃO PAULO – UNIFESP, Author
4. MAIA, ANTONIO AUGUSTO MENDES, UNIVERSIDADE DE SÃO PAULO – USP, Author