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Climate change associated with human activities alters marine ecosystems and causes imbalances and abrupt changes in sea conditions. Scarce freshwater resources for human consumption often prompt the construction of desalination plants, which discharge significant amounts of brine into the sea, potentially elevating salinity levels. Furthermore, global trade together with higher temperature and pollution can facilitate the spread of parasites. The aim of this study was to assess the potential effects of salinity, an abiotic stressor, and Scaphanocephalus sp. parasitic infection responsible for black spot disease, a biotic stressor, on Coris julis, a common fish in the Balearic Islands (Spain). Fish were sampled from an area affected by a desalination plant, one with a high rate of parasite infection and a control area, and biomarkers were analysed in the liver, gills and epithelial mucosa. Both salinity and the parasite induced increases in catalase (CAT) and glutathione s-transferase activities in the liver, while superoxide dismutase (SOD) did not show significant changes. The effects of salinity were evident to a greater extent in the gills with an increase in the activity of all enzymes, as well as in the production of reactive species. The effects of the parasite were mainly observed in the mucus with significant increases in CAT and SOD activities. Regarding immune response markers in the mucus, both stressors induced an increase in lysozyme and alkaline phosphatase activities, and in the case of the parasite, also an increase in immunoglobulins. Malondialdehyde, as an indicator of oxidative damage, remained unchanged. In conclusion, both abiotic and abiotic stress induce a stress situation in C. julis that responds by activating its antioxidant and immune defence mechanisms but does cause oxidative damage. The differential tissue response to different stressors highlights the value of analysing multiple tissues to detect early indicators of diverse impacts on marine fauna., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Ectoparasites cause serious problems during the aquaculture production of food fishes. In this study, we set out to develop and test protocols for maintenance and sampling European catfish ( Silurus glanis L., 1758) stocks infected with a gill monogenean, Thaparocleidus vistulensis (Siwak 1932) Lim 1996. When we compared the feasibility of two cohabitation-based parasite culture systems ( i.e. , static vs. flow-through), we found that the life cycle of T. vistulensis was completed in both habitats. In our experience, static tank systems with regular water exchange allowed better daily quality control of the parasite culture than continuous flow-through systems. We investigated the microhabitat preference of T. vistulensis on the gills of infected European catfish. A balanced distribution on the two lateral gill sets and a decreasing trend in parasite numbers from anterior gill holobranches towards the posterior ones was observed. Using these results, we developed a minimally invasive sampling protocol to estimate the parasite load of individuals. The biopsy aimed at four sectors (#6, #7, #10, and #11) situated within the distal and middle zones of the first holobranch on the left side, encompassing both rows of filaments. Biopsy-based estimates of parasite loads were validated by comparing them to full parasite counts of the same individuals and showed statistically significant correlations. Our biopsy-based method is designed to identify experimental animals with similar parasite loads and create groups of hosts with comparable burdens. This setup is expected to generate reduced between-group differences for expensive experiments ( e.g. , high throughput transcriptomic or epigenetic studies). We propose that the biopsy-based pre-sorting procedure should be considered in similar experiments with other cultured fish species and their gill monogeneans following a thorough fine-tuning of the experimental conditions., Competing Interests: The authors declare there are no competing interests., (©2024 Bognár et al.)

Fish are exposed to various parasites such as monogeneans which are flatworms that preferentially affect the gills and skin of these hosts. This study represents the first investigation concerning the distribution of monogenean infracommunities of Enteromius guirali in Cameroon. A total of 100 fish were collected from Cesala River and preserved in 8% formalin solution. Parasite community consisted of Dactylogyrus mendehei and D. nyongensis. These monogenean species adopted an aggregated distribution. Their mean intensities and prevalence increased with host size. Both sides of E. guirali were similarly infested, and no preference for gill arches was recorded for each parasite species. Posterior hemibranch was always the most parasitized, showing the highest parasitic load. Median sector and distal filamentous zone were highly colonized by both monogenean species. This study contributes to understand that the large gill surface offered by great hosts, heterogeneity, bilateral symmetrically of the host's gill system on one hand, and the morphology of haptoral parts and reproduction of parasites, on the other hand, are the main factors which determine the distribution of studied component community., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Three new species of Jainus Mizelle, Kritzky & Crane, 1968, are described parasitizing the gill filaments of Triportheus angulatus (Spix & Agassiz) (Characiformes: Triportheidae), an omnivorous fish endemic to the Amazon River basin. Jainus iquitensis n. sp. is characterized by the morphology of the vagina, which is bell-shaped, with a canal as a sclerotized tube and the morphology of hook pair VII, which in the new species presents an inflated base, a characteristic not observed in other congeners. Jainus loretoensis n. sp. is unique among Jainus species due to the morphology of its Y-shaped ventral anchors, with an arrow-shaped superficial root and a finger-shaped deep root. Jainus sardinae n. sp. is characterized by presenting a slender, small J-shaped tube with a sigmoid accessory piece and a ventral anchor that is Y-shaped, with inconspicuous finger-shaped deep root and superficial root with rounded ending with a chin-shaped projection. These findings add three new species to the previously reported two Jainus species from Peru., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Proliferative gill disease (PGD), caused by the myxozoan Henneguya ictaluri , has been the most notorious parasitic gill disease in the US catfish aquaculture industry. In 2019, an unusual gill disease caused by massive burdens of another myxozoan, Henneguya exilis , was described in channel ( Ictalurus punctatus ) × blue ( Ictalurus furcatus ) hybrid catfish. Targeted metagenomic sequencing and in situ hybridization (ISH) were used to differentiate these conditions by comparing myxozoan communities involved in lesion development and disease pathogenesis between massive H. exilis infections and PGD cases. Thirty ethanol-fixed gill holobranchs from 7 cases of massive H. exilis infection in hybrid catfish were subjected to targeted amplicon sequencing of the 18S rRNA gene and compared to a targeted metagenomic data set previously generated from clinical PGD case submissions. Furthermore, serial sections of 14 formalin-fixed gill holobranchs (2 per case) were analyzed by RNAscope duplex chromogenic ISH assays targeting 8 different myxozoan species. Targeted metagenomic and ISH data were concordant, indicating myxozoan community compositions significantly differ between PGD and massive branchial henneguyosis. Although PGD cases often consist of mixed species infections, massive branchial henneguyosis consisted of nearly pure H. exilis infections. Still, H. ictaluri was identified by ISH in association with infrequent PGD lesions, suggesting coinfections occur, and some cases of massive branchial henneguyosis may contain concurrent PGD lesions contributing to morbidity. These findings establish a case definition for a putative emerging, myxozoan-induced gill disease of farm-raised catfish with a proposed condition name of massive branchial henneguyosis of catfish (MBHC)., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

A new species, Myxobolus liuyangensis sp. n., was found in the gills of the exotic mrigal carp Cirrhinus mrigala during a survey of the fauna of exotic fish myxospore in China. Plasmodia were elongated pyriform, measuring 0.42 mm long and 0.15 mm wide. The mature spores were elongated pyriform in the frontal view, tapered forward, rounded posterior end, and fusiform in the sutural view, measuring 17.3 ±0.5 (16.5-18.3) μm long, 6.2 ±0.3 (5.2-6.8) μm wide, and 4.8 ±0.2 (4.4-5.1) μm thick. The two equal polar capsules of elongated pyriform in shape measured 11.3 ±0.5 (10.6-12.3) μm long and 2.5 ±0.3 (2.0-3.1) μm wide, occupying more than half the capacity of the spores. The polar filaments were coiled with fifteen to sixteen turns. No mucous envelope and caudal appendages were found. The consensus SSU rDNA gene sequence obtained here for M. liuyangensis sp. n. did not match any sequences available in GenBank, but was most closely related to M. catlae that infects the gills of C. cirrhosis (MT003664, 97.99% similarity). Phylogenetic analysis indicated that the C. mrigala-infecting Myxobolus species were not clustered together, but dispersed in different clades. The present species clustered with M. catlae and M. orissae within the clade I of elongated pyriform spore shapes, revealing spore shapes may play an important role during the evolution of Myxobolus species. This is the second myxosporean infection report in the exotic mrigal carp C. mrigala., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

A new species of Gyrodactylus is described from the gills of the near-threatened Clanwilliam sawfin, Cheilobarbus serra (Smiliogastrinae) collected from the Matjies River, Cape Fold Ecoregion, Western Cape Province, South Africa. Morphometry and morphology of the haptoral hard parts (hamuli, bars and marginal hooks) of Gyrodactylus serrai n. sp. differ from the other known species of the genus in the smaller size of hamuli and the shape and size of marginal hooks. Furthermore, ITS rDNA for the new species is unique among available Gyrodactylus spp. data in GenBank. Based on the uncorrected p-distances, G. serrai n. sp. is genetically most closely related to Gyrodactylus moroccensis Rahmouni, 2023 and Gyrodactylus pseudomoroccensis Rahmouni, 2023 from two species of Luciobarbus (Barbinae) from northern Africa, with interspecific divergence of 8.7% and 8.8%, respectively. The presence of a median ridge in the terminal part of the ventral bar membrane at G. serrai n. sp. most probably represents a morphological link to the North African Gyrodactylus spp. that suggests a morphogenetic association across the African continent as a result of ancient waterways that facilitated the dispersion of cyprinids and their parasite fauna or an independent evolution event retaining similarities from a common ancestor. The description of Gyrodactylus serrai n. sp. represents only the second species of Gyrodactylus described from an endemic South African cyprinid host, underscoring the need for focused research on this group of fishes to provide a sound understanding of the parasitic communities of these highly threatened and poorly studied hosts., (© 2024. The Author(s).)

Parasitism involves diverse evolutionary strategies, including adaptations for blood feeding, which provides essential nutrients for growth and reproduction. Sparicotyle chrysophrii (Polyopisthocotyla: Microcotylidae), an ectoparasitic flatworm, infects the gills of gilthead seabream ( Sparus aurata ), significantly affecting fish health, welfare and Mediterranean cage farm profitability. Despite its impact, limited information exists on its feeding behaviour. This study demonstrates the presence of blood and exogenous haem groups in S. chrysophrii and explores its digestive tract using light and electron microscopy, elucidating its internal morphology and spatial arrangement. Elemental analysis of the digestive haematin cells shows residual oxidized haem depots as haematin crystals. Additionally, we studied the impact of the blood feeding on the host by estimating the average volume of blood intake for an adult parasite (2.84 ± 2.12µl·24h -1 ) and we described the significant drop of the plasmatic free iron levels in infected hosts. Overall, we demonstrate the parasite's reliance on its host blood, the parasite's buccal and digestive morphological adaptations for blood feeding and the provoked effect on the fish host's health.

Dicyemids (Phylum Dicyemida) are endosymbionts present in the kidneys of benthic cephalopods. They usually consist of 10 to 40 cells and are characterized by 2 distinct body types: vermiform individuals and infusoriform larvae. Vermiform individuals remain attached to the internal surface of the host's renal appendages, while infusoriform larvae leave the renal sac to search for a new host. To investigate how dicyemids respond to various host and environmental cues, we evaluated phototaxis, chemotaxis, thigmotaxis, and rheotaxis responses of vermiform individuals and infusoriform larvae of 2 dicyemid species in a laboratory setting. Vermiform individuals did not exhibit phototaxis and chemotaxis to the major components of the host: urine, tissue fluids, or extracts of the host gills. However, they showed positive thigmotaxis and positive rheotaxis to slow water flow, probably contributing to enabling attachment to the renal appendages and remaining in the renal sac, respectively. The infusoriform larvae exhibited negative chemotaxis to host blood and negative thigmotaxis, but there was no evidence of phototaxis and rheotaxis. Negative thigmotaxis may facilitate the release of infusoriform embryos from the renal appendages. Negative chemotaxis to the host blood suggests that the infusoriform larvae do not enter through the vascular system to gain access to the renal sac, so the process by which infusoriform larvae enter the cephalopod host is yet to be determined., (© American Society of Parasitologists 2024.)

Piaractus brachypomus (Pacú) is the main native fish species cultivated in Peru and holds great potential for growth in aquaculture from the Peruvian Amazon. Between October 2021 and January 2022 in two fish producing farms in the Amazon region of San Martín in Peru, P. brachypomus individuals were examined for parasite evaluation. A total of 6366 monogeneans were isolated from the gills of 30 fish, revealing a prevalence of 100%, with an abundance and mean intensity of 212 parasites per fish. Monogeneans were morphologically identified as Mymarothecium viatorum and Anacanthorus penilabiatus. The genetic divergence in the 28S rDNA gene found among A. penilabiatus sequences was 0.1% and among Anacanthorus spp. it ranged from 0.9% to 7.5%. The genetic divergence found among the M. viatorum sequences was 0.3%. These finding represents the first molecular data of M. viatorum and A. penilabiatus in Peru using the 28S rDNA gene of these monogeneans. The new sequences obtained will contribute to future studies on the phylogenetic relationships among dactylogyrids. However, further research with a broader range of host-parasite samples and additional genetic markers is needed to clarify these relationships and provide stronger support for the phylogenetic positions., Competing Interests: Declaration of competing interest The authors of the manuscript “Molecular Identification of Mymarothecium viatorum and Anacanthorus penilabiatus in Extensive Native Fish Farming Systems of the Peruvian Amazon” declare that this information has not been previously published, has not been submitted to another journal for publication, and the publication of this manuscript is approved by all authors and by the institutions linked in this document. If the manuscript is accepted for publication it will not be considered for republication in any modified version., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Purpose: Studies on monogeneans parasitizing representatives of Siluriformes in Africa remain scarce and fragmentary. In order to contribute to fill this gap, we screened Heterobranchus longifilis from the Lindi River in the Democratic Republic of the Congo., Methods: Heterobranchus longifilis was purchased from fishermen in DR Congo, province of Tshopo, in Kisangani town, the Lindi River. The monogeneans were individually isolated from the gill and transferred directly onto a slide in a drop of Hoyer's medium., Results: Quadriacanthus lindiensis n. sp. is morphologically similar to Quadriacanthus longifilisi. However, it is distinguished from the latter by its non-sclerotized vagina, its dorsal cunei shape and the size of its bars., Conclusion: Only Q. lindiensis n. sp. was found on the gills of the single individual of H. longifilis screened. In the future, a representative sampling should enable us to verify if Q. lindiensis n. sp. co-occurs with other species known to parasitize H. longifilis., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Introduction: The present study describes three new dactylogyrid species infecting the gill filaments of cichlid fishes (Cichliformes: Cichlidae) from the Amazon basin, Peru: Sciadicleithrum amazoniensis n. sp. on Biotodoma cupido (Heckel, 1840), and Sciadicleithrum feliciajaramae n. sp. and Sciadicleithrum souzatecci n. sp. on Bujurquina peregrinabunda Kullander, 1986., Materials and Methods: Some monogeneans were stained with Gomori's trichrome and mounted in Canada Balsam to determine internal soft structures. Others were cleared in Hoyer's medium for the study of sclerotized structures. Drawings were made using a drawing tube and a microprojector., Results: Sciadicleithrum amazoniensis n. sp. is characterized by the presence of a male copulatory organ (MCO) with a coil of approximately 2 counterclockwise rings, an accessory piece articulated to base of the MCO with an expanded proximal end and a bifurcated distal end, and a sinistral vaginal aperture. Sciadicleithrum feliciajaramae n. sp. can be differentiated from all its congeners by its J-shaped MCO with about half a counterclockwise loop and a rod-shaped accessory piece articulated to the base of the MCO, with the distal end bent. Sciadicleithrum souzatecci n. sp. differs from all other members of Sciadicleithrum by having an elongated MCO with about a clockwise loop and a funnel-shaped base. Additionally, Sciadicleithrum souzatecci n. sp. is characterized by its weakly sclerotized, C-shaped accessory piece with a robust middle process., Conclusions: Present findings are added to the other 26 species previously known in Sciadicleithrum.This is the first data on the parasites of B. peregrinabunda., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Amyloodiniosis, caused by the ectoparasite Amyloodinium ocellatum, affects the healthy development of mariculture. This study used a local infection method to identify the pathogenic target organ responsible for the death of infected fish. Comparing the relationship between the abundance of trophonts in gills and skin with the mortality of infected fish using local infection showed that severe gill infections cause the mortality of infected fish. At the 40 % survival rate of infected fish, the parasite abundance in the gill was 14,167 ± 4371. The gill filaments of the infected fish were structurally disordered, with pronounced lesions associated with the presence of trophonts, such as epithelial cell degeneration and massive lymphocytic infiltration. However, the skin showed no obvious pathological changes. The TUNEL assay showed a significant presence of apoptotic cells concentrated in the area of A. ocellatum infection. The trophonts on the gills developed faster than those parasitising the skin and fins. Microbiome analysis revealed that at the phylum level, Proteobacteria, Bacteroidota, and Firmicutes are abundant in the skin, while Verrucomicrobiota, Bacteroidota, and Proteobacteria are abundant in the gills of A. latus. Furthermore, A. ocellatum infection significantly reduced (p < 0.05) the richness and diversity of the gill microbial community of A. latus. Infection by A. ocellatum increased the relative abundance of several putative pathogenic bacteria (Flavobacterium and Nocardia) in the gill and skin of A. latus, possibly increasing the likelihood of disease in the host. In conclusion, these results evidenced that severe gill infections by A. ocellatum cause mortality in infected fish, which clarifies the direction for exploring the pathogenesis of amyloodiniosis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

A new species of hemiurid trematode found on the gills and in the aorta of the pelagic thresher Alopias pelagicus from the eastern Pacific, off Costa Rica, is described based on an integrative taxonomic approach that includes the use of light and scanning electron microscopy, and 28S rDNA sequencing. Phylogenetic analysis was also performed to explore, for the first time, the relationships of a member of the subfamily Otiotrematinae within the suborder Hemiurata. Paronatrema davidbowiei n. sp. can be distinguished from the congeners by having tegumental spines on the dorsal surface of the forebody, papillae on the oral sucker, and different morphology or number of testicular follicles. BLAST analysis revealed that sequences of Paronatrema davidbowiei n. sp. had the highest degree of similarity with Hirudinella spp. (Hirudinellidae). Results from Maximum Likelihood and Bayesian phylogenetic analyses, returning trees with the exact same topology and strong branch support, distinguished between the two superfamilies included in the suborder Hemiurata: Azygioidea and Hemiuroidea. Our analysis placed the new species in a clade with Copiatestes filiferus, the only existing sequence of the family Syncoeliidae., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest., (Copyright © 2024. Published by Elsevier B.V.)

From genus Myxobolus, cnidarians of Myxozoa class, is well known for infecting economically important fish species and, as result, relevant losses in aquaculture production can be observed. They are present in a big range of fish in its natural habitat, including the migratory Brachyplatystoma rousseauxii catfish. This study aimed is to develop an integrative characterization of a new species of Myxobolus, located in B. rousseauxii's gills. To accomplish this, 30 specimens of B. rousseauxii catfish were collected from Mosqueiro Island in Pará, Brazil; necropsied and analyzed for morphology, histology and molecular characteristics. Cysts with conjunctival capsule development made up of fibroblasts were observed at the gill arches; such proliferation caused bone tissue loss and cartilage compression. The cysts contained Myxobolus myxospores measuring 9.9 μm of length and 9.6 μm of width, whereas polar capsules were 5.4 μm long and 3.4 μm wide, with 8 to 9 coils of polar tubules. Phylogenetic analyses revealed that new species were included in a subclade alongside species from the same geographic location and infection site that infect Siluriformes fish. Morphological and molecular differences revealed that Myxobolus spp. parasite-host associations through histopathology supporting the designation of a new M. rousseauxii n. sp. species in B. rousseauxii, a commercially important fish., Competing Interests: Declaration of competing interest None., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Haliotrema Pteroisi: Paperna, 1972 (Monogenoidea: Dactylogyridae) was found parasitizing the gill lamellae of devil firefish, Pterois miles (Bennet) (Perciformes: Scorpaenidae), in the Red Sea off Safaga (26°44'N, 33°56'E), Egypt. The parasite species was described based on morphological features of available specimens and transferred to PlatycephalotremaKritsky and Nitta, 2019 (Dactylogyridae) as Platycephalotrema pteroisi (Paperna, 1972) n. comb. The occurrence of Pl. pteroisi off Safaga, Egypt, represented a range extension for the helminth of about 160 km to the southwest of the southern end of the Gulf of Aqaba. The transfer of the species to Platycephalotrema based on an evaluation of morphological features was supported by an analysis of molecular sequences of the 28S rDNA gene of Pl. pteroisi and 49 other dactylogyrid species. Maximum-likelihood, Bayesian inference, and maximum parsimony analyses of this dactylogyrid sequence data revealed H. pteroisi to nest with significant support within the clade of Platycephalotrema spp. During the literature review of dactylogyrid species infecting scorpionfishes, it was determined that Ancyrocephalus sp. of Dyer et al. from luna lion fish Pterois lunulata Temminck and Schlegel collected off Okinawa-jima, Japan represented an undescribed species of Platycephalotrema., (© American Society of Parasitologists 2024.)

Background: Gills monogenean infestation causes significant mortalities in cultured fishes as a result of respiratory manifestation. Medicinal plants are currently being heavily emphasized in aquaculture due to their great nutritional, therapeutic, antimicrobial activities, and financial value., Methods: The current study is designed to assess the effect of garlic (Allium sativum) and onion (Allium cepa) extracts as a water treatment on the hematological profile, innate immunity, and immune cytokines expression besides histopathological features of gills of Nile tilapia (Oreochromis niloticus L.) infected with gills monogenetic trematodes (Dactylogyrus sp.). Firstly, the 96-hour lethal concentration 50 (96 h-LC 50 ) of garlic extract (GE) and onion extract (OE) were estimated to be 0.4 g/ L and 3.54 g/ L for GE and OE, respectively. Moreover, the in-vitro anti-parasitic potential for (GE) was found between 0.02 and 0.18 mg/mL and 0.4 to 1.8 mg/mL for OE. For the therapeutic trial, fish (n = 120; body weight: 40-60 g) were randomly distributed into four groups in triplicates (30 fish/group, 10 fish/replicate) for 3 days. Group1 (G1) was not infected or treated and served as control. G2 was infected with Dactylogyrus spp. and not exposed to any treatment. G3, G4 were infected with Dactylogyrus sp. and treated with 1/ 10 and 1/ 5 of 96 h LC 50 of OE, respectively. G5, G6 were infected with Dactylogyrus sp. and treated with 1/ 10 and 1/ 5 of 96 h LC 50 of GE, respectively., Results: No apparent signs or behaviors were noted in the control group. Dactylogyrus spp. infected group suffered from clinical signs as Pale color and damaged tissue. Dactylogyrus spp. infection induced lowering of the hematological (HB, MCH, MCHC and WBCs), and immunological variables (lysozyme, nitric oxide, serum Anti- protease activities, and complement 3). the expression of cytokine genes IL-ß and TNF-α were modulated and improved by treatment with A. sativum and A. cepa extracts. The obtained histopathological alterations of the gills of fish infected with (Dactylogyrus spp.) were hyperplasia leading to fusion of the gill filament, lifting of epithelial tissue, aneurism and edema. The results indecated that G4 and G5 is more regenarated epithelium in compare with the control group., Conclusion: A. sativum and A. cepa extracts enhance the blood profile and nonspecific immune parameters, and down-regulated the expression level of (IL-1β and TNF-α)., (© 2024. The Author(s).)

Troglocephalinae n. subfam. is proposed for Spinuris Doran, 1953, Neoheterocotyle Hargis, 1955, Anoplocotyloides Young, 1967, Troglocephalus rhinobatidis Young, 1967 (previously incertae sedis), Nonacotyle pristis Ogawa, 1991, Mehracotyle insolita Neifar, Euzet & Ben Hassine, 2002, Scuticotyle cairae n. gen. et sp., and Brancheocotyle imbricata n. gen. et sp. All members of the proposed new subfamily are gill parasites of shovelnose rays of the order Rhinopristiformes. The subfamilies Heterocotylinae Chisholm, Wheeler & Beverley-Burton, 1995, and Dasybatotreminae Bychowsky, 1957, are amended to exclude Spinuris, Nonacotyle, Neoheterocotyle, and Anoplocotyloides and Mehracotyle, respectively. Heterocotylinae includes gill parasites of members of the orders Myliobatiformes and Torpediniformes. Dasybatotreminae includes parasites of the gills and pharyngeal cavity of members of the orders Myliobatiformes and Rajiformes. A revised phylogeny of the Monocotylidae Taschenberg, 1879 is presented and discussed, based on 28S rDNA sequences, including new sequences for Myliocotyle pteromylaei Neifer, Euzet & Ben Hassine, 1999, Heterocotyle tokoloshei Vaughan & Chisholm, 2010, Neoheterocotyle robii Vaughan & Chisholm, 2010, and the two newly proposed species and genera. Additional locality records are also provided for Monocotylidae from off South Africa., (© 2024. The Author(s).)

During March 2023, 7 green sunfish (Lepomis cyanellus) and 2 bluegill (Lepomis macrochirus) were collected from the Black River (White River drainage) in Lawrence County, Arkansas. In addition, during March 2023 and again in May-June 2023, 13 L. cyanellus and 6 L. macrochirus were taken from Butcherknife and Big Fork creeks (Ouachita River drainage), Polk County, Arkansas, 9 L. cyanellus were collected from the Caddo River, Montgomery County, Arkansas, and 5 green sunfish were taken from Clear Creek at Savoy, Washington County, Arkansas. All fish had their gill, gallbladder, fins, integument, musculature, and other major organs examined for myxozoans. The gill of 1 of 34 (3%) L. cyanellus was infected with a new myxozoan, Myxobolus fergusoni n. sp. Qualitative and quantitative morphological data were obtained from fresh myxospores, and molecular data consisted of a 1,933-base-pair sequence of the partial small subunit (SSU) ribosomal RNA (rRNA) gene. Phylogenetic analysis grouped M. fergusoni n. sp. with other centrarchid-infecting myxobolids from North America and placed this cluster in a larger clade comprising myxozoans that infect North American and European esocids, a North American aphredoderid, European percids, and a gasterosteid from Japan. Myxobolus fergusoni n. sp. infects the gill arches of L. cyanellus, similar to Myxobolus cartilaginis (Hoffman, Putz, and Dunbar, 1965), which was described from head cartilage, gill arches, and large fin rays of L. cyanellus. Another is Myxobolus mesentericusKudo, 1920, which was described from the viscera of green sunfish. A large polysporic plasmodium filled with myxospores was present in a basifilamental location associated with multiple gill filaments at their junction with the gill arch. The intact plasmodium replaced connective tissue within the arch but elicited only mild proliferation of overlying epithelium and a minimal host inflammatory response. This is the third time a myxozoan has been described from L. cyanellus, as well as being the first time it has been described from an Arkansas specimen., (© American Society of Parasitologists 2024.)

Monogenean trematodes, particularly those belonging to the Diplectanidae family, are significant metazoan parasites with substantial implications for aquaculture expansion. This study, investigatied the occurrence, prevalence, and pathological impact of Diplectanum spp. in European seabass (Dicentrarchus labrax) across three distinct Egyptian fish farms. During 2021-2022, we sampled 1800 European seabass (Dicentrarchus labrax) from three Egyptian fish farms (600 fish per farm). Farms 1 and 2 used semi-intensive earthen pond systems, while Farm 3 utilized an intensive floating cage system. Employing Clinical, post-mortem, parasitological, and molecular examination technique. Pathological lesions were identified, including skin and gill discoloration, emaciation, and internal organ abnormalities. Seasonal prevalence exhibited significant variations between farms, with highest rates observed in spring and Farm 3 reached an overall peak prevalence of 84.67 %. Parasitological examination distinguished two Diplectanum species morphologically, while molecular techniques exhibited limited specificity. Histopathology unveiled damage to gill, liver, spleen, kidney, and intestine, attributed to Diplectanum haptors including inflammation and internal bleeding, potentially leading to secondary infections. Molecular identification via PCR targeting ITS and 28SrDNA genes, revealing similar band sizes for the two Diplectanum species, indicating limited intraspecific genetic diversity. The study emphasizes investigating parasitic infections' prevalence and impact in aquaculture, necessitating robust molecular techniques for species differentiation. This study underscores the importance of investigating the prevalence and impact of parasitic infections in aquaculture. It highlights the need for robust molecular techniques to differentiate species. By focusing on Diplectanum spp. infections in D. labrax, the study offers valuable insights into managing parasites in aquaculture effectively., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper, (Copyright © 2024 Elsevier B.V. All rights reserved.)

The development and application of functional feed ingredients represents a great opportunity to advance fish growth and health, boost the immune system, and induce physiological benefits beyond those provided by traditional feeds. In the present study, we looked at the feasibility of in vitro methods for screening the qualities of functional feed ingredients using the fish cell line RTgill-W1, which has never been used in fish nutrition, and the culture of Paramoeba perurans. Five functional feed ingredients (arginine, β-glucan, vitamin C, and two phytogenic feed additives) were selected to investigate their effects on cell viability and reactive oxygen species production. Three of the selected ingredients (arginine and two phytogenic feed additives) were additionally tested to assess their potential amoebicidal activity. As these functional ingredients are the core of a commercially available feed (Protec Gill, Skretting AS), their beneficial effects were further assessed in a field trial in fish affected by complex gill disease. Here, the analyzed parameters included the evaluation of macroscopic and histopathological gill conditions, pathogen detections, and analyses of plasma parameters. RTgill-W1 cell line assays were a good tool for screening functional ingredients and provided information about the optimal ingredient concentration ranges, which can be helpful for adjusting the concentrations in future feed diets. Through the culture of P. perurans, the tested ingredients showed a clear amoebicidal activity, suggesting that their inclusions in dietary supplements could be a viable way to prevent microbial infections. A three-week period of feeding Protec Gill slowed the disease progression, by reducing the pathogen load and significantly improving gill tissue conditions, as revealed by histological evaluation. The use of diets containing selected functional ingredients may be a feasible strategy for preventing or mitigating the increasingly common gill diseases, particularly in cases of complex gill disease, as documented in this study., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Vitale et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Nile tilapia (Oreochromis niloticus) is valued in aquaculture because of its quick development and ability to thrive in various environments. Myxosporeans are among the fish parasites that affect fish productivity, as they impact fish growth and reproduction, resulting in large fish deaths in farms and hatcheries. This study has been focused on morpho-molecular identification for the myxosporean parasites infecting Nile tilapia from three governorates in Egypt and assessment of gene expression of different cytokines (Interleukin-1βeta (IL-1β), major histocompatibility complex class II (MHC-II), and clusters of differentiation 4 (CD-4) and 8 (CD-8)) in tissues. Additionally, this work aimed to correlate the developed histopathological alterations and inflammatory reactions in gills with immunohistochemical expression of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-α). Finally, the infected fish's cortisol levels and blood glucose were assessed. Results of BLAST sequence analysis of the 18S rRNA for the collected protozoans confirmed Myxobolus agolus, M. brachysporus, M. tilapiae, and Henneguya species. The molecular characterization of the immunological status of gills revealed marked upregulation of different inflammatory cytokines in the gills of infected fish. There was a significantly increased serum cortisol and glucose level in infected fish compared with control, non-infected ones. Severe histopathological alterations were observed in the infected fish gills, associated with increased expression of iNOS and TNF-α and related to myxosporean infection. The present study provides new insights into oxidative stress biomarkers in Nile tilapia infected with Myxosporeans and elucidates the gill's immune status changes as a portal of entry for protozoa that contribute to tissue damage., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Ramadan et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Nodular gill disease (NGD) is an emerging condition associated with amoeba trophozoites in freshwater salmonid farms. However, unambiguous identification of the pathogens still must be achieved. This study aimed to identify the amoeba species involved in periodic NGD outbreaks in two rainbow trout (Oncorhynchus mykiss) farms in Northeastern Italy. During four episodes (February-April 2023), 88 fish were euthanized, and their gills were evaluated by macroscopic, microscopic and histopathological examination. The macroscopic and microscopic severity of the lesions and the degree of amoebae infestation were scored and statistically evaluated. One gill arch from each animal was put on non-nutrient agar (NNA) Petri dishes for amoeba isolation, cultivation and subsequent identification with SSU rDNA sequencing. Histopathology confirmed moderate to severe lesions consistent with NGD and mild to moderate amoeba infestation. The presence of amoebae was significantly correlated with lesion severity. Light microscopy of cultured amoebae strains and SSU rDNA analysis revealed the presence of a previously characterized amoeba Naegleria sp. strain GERK and several new strains: two strains from Hartmannelidae, three vannelid amoebae from the genus Ripella and cercozoan amoeba Rosculus. Despite the uncertainty in NGD etiopathogenesis and amoebae pathogenic role, identifying known and new amoebae leans towards a possible multi-aetiological origin., (© 2024 The Authors. Journal of Fish Diseases published by John Wiley & Sons Ltd.)

Purple-spotted bigeyes Priacanthus tayenus Richardson (Priacanthidae) and bartail flathead Platycephalus indicus (Linnaeus) (Platycephalidae) were collected from the Arabian Gulf and examined for species of Monogenoidea (Polyonchoinea) from February to December 2020. Diplectanum robustitubum Wu & Li, 2003 and an undescribed species of Platycephalotrema Kritsky & Nitta, 2019 were recovered from the gill lamellae of these hosts, respectively. Diplectanum robustitubum from Iraq was redescribed and transferred to Oliveriplectanum Domingues & Boeger, 2008 (Diplectanidae) as Oliveriplectanum robustitubum (Wu & Li, 2003) n. comb. Platycephalotrema parile n. sp. (Dactylogyridae) from Iraq and Kuwait was described and differentiated from the similar species, Haliotrema indicum Tripathi, 1959, Platycephalotrema ogawai Kritsky & Nitta, 2019, and Platycephalotrema platycephali (Yin & Sproston, 1948) Kritsky & Nitta, 2019, based primarily on the comparative morphologies of the vaginal sclerites. Haliotrema indicum was transferred to Platycephalotrema as Platycephalotrema indicum (Tripathi, 1959) n. comb. and Haliotrema swatowense Yao, Wang, Xia, & Chen, 1998 was considered a junior subjective synonym of P. indicum. The finding of O. robustitubum in the Arabian Gulf represents a new geographic record for the species., Background: The present paper represents the third installment concerning the monogenoids collected during surveys to explore their diversity on the marine and freshwater fishes of Iraq. Previous installments on the monogenoids emanating from the surveys included the dactylogyrid and gyrodactylid species parasitizing mugilid fishes., Purpose: The purpose of this paper is to further document the diversity of monogenoids infecting the fishes of Iraq., Methods: Marine fishes were necropsied for parasites, and standard procedures for collecting, mounting, drawing, and measuring of monogenoids were employed., Results: Oliveriplectanum robustitubum n. comb. (Diplectanidae) and Platycephalotrema parile n. sp. (Dactylogyridae) were collected. The occurrence of O. robustitubum in the Arabian Gulf represented a new locality record for the species., Conclusion: The recorded presence of O. robustitubum and P. parile n. sp. suggests that the diversity of monogenoids in Iraq is under estimated in the literature., (© 2024. The Author(s).)

Purpose: This study investigated the anthelmintic efficacy of therapeutic baths with the essential oil of Piper marginatum Jacq against the monogeneans Anacanthorus spathulatus Kritsky, Thatcher & Kayton, 1979, Notozothecium janauachensis Belmont-Jégu, Domingues & Laterça 2004, Mymarothecium boegeri Cohen & Kohn, 2005 and Linguadactyloides brinkmanni Thatcher & Krytsky, 1983 in Colossoma macropomum Cuvier, 1818, and its hematological and histopathological effects on this fish., Methods: Short six therapeutic baths with 100 mg/L of the essential oil of P. marginatum and two control groups (water from the cultivation tank and water from the cultivation tank + 70% alcohol) were used for 20 min every two days., Results: The therapeutic baths with 100 mg/L of the essential oil of P. marginatum had efficacy of 42.8% against monogeneans of C. macropomum gills. Toxicity was low for C. macropomum, because there were few physiological and histopathological changes that did not compromise the functioning of the gills of this fish., Conclusion: Short therapeutic baths with 100 mg/L of the essential oil of P. marginatum had low efficacy for controlling monogeneans in C. macropomum and thus cannot be recommended., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Myxozoa, a unique group of obligate endoparasites within the phylum Cnidaria, can cause emerging diseases in wild and cultured fish populations. Recently, the myxozoan Myxobolus bejeranoi has been identified as a prevalent pathogen infecting the gills of cultured hybrid tilapia, leading to systemic immune suppression and considerable mortality. Here, we employed a proteomic approach to examine the impact of M. bejeranoi infection on fish gills, focusing on the structure of the granulomata, or cyst, formed around the proliferating parasite to prevent its spread to surrounding tissue. Enrichment analysis showed increased immune response and oxidative stress in infected gill tissue, most markedly in the cyst's wall. The intense immune reaction included a consortium of endopeptidase inhibitors, potentially combating the myxozoan arsenal of secreted proteases. Analysis of the cyst's proteome and histology staining indicated that keratin intermediate filaments contribute to its structural rigidity. Moreover, we uncovered skin-specific proteins, including a grainyhead-like transcription factor and a teleost-specific S100 calcium-binding protein that may play a role in epithelial morphogenesis and cysts formation. These findings deepen our understanding of the proteomic elements that grant the cyst its distinctive nature at the critical interface between the fish host and myxozoan parasite.

Introduction: Little is known about the proteomic changes at the portals of entry in rainbow trout after infection with the myxozoan parasites, Myxobolus cerebralis , and Tetracapsuloides bryosalmonae . Whirling disease (WD) is a severe disease of salmonids, caused by the myxosporean M. cerebralis , while, proliferative kidney disease (PKD) is caused by T. bryosalmonae , which instead belongs to the class Malacosporea. Climate change is providing more suitable conditions for myxozoan parasites lifecycle, posing a high risk to salmonid aquaculture and contributing to the decline of wild trout populations in North America and Europe. Therefore, the aim of this study was to provide the first proteomic profiles of the host in the search for evasion strategies during single and coinfection with M. cerebralis and T. bryosalmonae ., Methods: One group of fish was initially infected with M. cerebralis and another group with T. bryosalmonae . After 30 days, half of the fish in each group were co-infected with the other parasite. Using a quantitative proteomic approach, we investigated proteomic changes in the caudal fins and gills of rainbow trout before and after co-infection., Results: In the caudal fins, 16 proteins were differentially regulated post exposure to M. cerebralis , whereas 27 proteins were differentially modulated in the gills of the infected rainbow trout post exposure to T. bryosalmonae . After co-infection, 4 proteins involved in parasite recognition and the regulation of host immune responses were differentially modulated between the groups in the caudal fin. In the gills, 11 proteins involved in parasite recognition and host immunity, including 4 myxozoan proteins predicted to be virulence factors, were differentially modulated., Discussion: The results of this study increase our knowledge on rainbow trout co-infections by myxozoan parasites and rainbow trout immune responses against myxozoans at the portals of entry, supporting a better understanding of these host-parasite interactions., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Saleh, Hummel, Schlosser, Razzazi-Fazeli, Bartholomew, Holzer, Secombes and El-Matbouli.)

The genus Ancyrocephalus sensu lato is a large assemblage of species of dactylogyrid monopisthocotyleans without clear taxonomic boundaries. Despite an urgent need for revision, only three representatives of this taxon have been molecularly characterised so far. We found specimens of Ancyrocephalus curtus , a previously non-genotyped species, in gills of Perccottus glenii caught in the River Syumnyur, Amur Basin, Russia. The aim of this study was to assess the phylogenetic position of this parasite using partial sequences of 28S rRNA gene. In the phylogenetic tree, A. curtus appeared as a sister taxon to the dactylogyrine genus Gobioecetes. The new molecular evidence supports the hypothesis about the non-monophyletic status of Ancyrocephalus sensu lato.

Two new species of Urocleidoides are described from the gills of Pseudanos trimaculatus (Characiformes: Anostomidae) from the coastal drainages of the Eastern Amazon, Brazil. Urocleidoides itabocaensis n. sp. is characterized by having a sclerotized, tubular, sigmoid male copulatory organ (MCO), a circular sclerotized tandem brim associated with the base of the MCO; an accessory piece articulated with the MCO, a V-shaped, divided into two subunits, distal subunit spoon-shaped; and a vaginal pore dextroventral with opening marginal. Urocleidoides omphalocleithrum n. sp. is characterized by presenting a C-shaped or sigmoid MCO; an accessory piece articulated with the MCO, L-shaped, divided into two subunits, distal subunit gutter-shaped; a vaginal pore dextroventral with opening marginal; and a ventral bar broadly V-shaped, with anteromedial projection. Molecular phylogenetic analysis based on partial 28S rDNA and COI mtDNA genes indicate that U. itabocaensis n. sp. and U. omphalocleithrum n. sp. are closely related and appear as a sister group to other Urocleidoides species (U. paradoxus, U. digitabulum and U. sinus) parasitizing anostomid fishes. This study represents the first record of monogenoids from the gills of P. trimaculatus for the Eastern Amazon., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Amyloodinium ocellatum is among the most devastating protozoan parasites, causing huge economic losses in the mariculture industry. However, the pathogenesis of amyloodiniosis remains unknown, hindering the development of targeted anti-parasitic drugs. The A. ocellatum in vitro model is an indispensable tool for investigating the pathogenic mechanism of amyloodiniosis at the cellular and molecular levels. The present work developed a new cell line, ALG, from the gill of yellowfin seabream (Acanthopagrus latus). The cell line was routinely cultured at 28°C in Dulbecco's modified Eagle medium (DMEM) supplemented with 15% fetal bovine serum (FBS). ALG cells were adherent and exhibited an epithelioid morphology; the cells were stably passed over 30 generations and successfully cryopreserved. The cell line derived from A. latus was identified based on partial sequence amplification and sequencing of cytochrome B (Cyt b). The ALG was seeded onto transwell inserts and found to be a platform for in vitro infection of A. ocellatum, with a 37.23 ± 5.75% infection rate. Furthermore, scanning electron microscopy (SEM) revealed that A. ocellatum parasitizes cell monolayers via rhizoids. A. ocellatum infection increased the expression of apoptosis and inflammation-related genes, including caspase 3 (Casp 3), interleukin 1 (IL-1), interleukin 10 (IL-10), tumour necrosis factor-alpha (TNF-α), in vivo or in vitro. These results demonstrated that the in vitro gill cell monolayer successfully recapitulated in vivo A. latus host responses to A. ocellatum infection. The ALG cell line holds great promise as a valuable tool for investigating parasite-host interactions in vitro., (© 2024 John Wiley & Sons Ltd.)

Freshwater bivalves play key ecological roles in lakes and rivers, largely contributing to healthy ecosystems. The freshwater pearl mussel, Margaritifera margaritifera, is found in Europe and on the East coast of North America. Once common in oxygenated streams, M. margaritifera is rapidly declining and consequently assessed as a threatened species worldwide. Deterioration of water quality has been considered the main factor for the mass mortality events affecting this species. Yet, the role of parasitic infections has not been investigated. Here, we report the discovery of three novel protist lineages found in Swedish populations of M. margaritifera belonging to one of the terrestrial groups of gregarines (Eugregarinorida, Apicomplexa). These lineages are closely related-but clearly separated-from the tadpole parasite Nematopsis temporariae. In one lineage, which is specifically associated with mortality events of M. margaritifera, we found cysts containing single vermiform zoites in the gills and other organs of diseased individuals using microscopy and in situ hybridization. This represents the first report of a parasitic infection in M. margaritifera that may be linked to the decline of this mussel species. We propose a tentative life cycle with the distribution of different developmental stages and potential exit from the host into the environment., (© 2024 The Authors. Journal of Eukaryotic Microbiology published by Wiley Periodicals LLC on behalf of International Society of Protistologists.)

We investigated disease trends of concern for fish or public health in a 5-y (2017-2021) prospective survey of fish in Cook County, IL, inland lakes. Lesions were assessed in relation to fish species, lake type and location, season and collection year, and lake water chemistry parameters. Fish included bullheads ( n  = 98), common carp ( n  = 99), bluegill ( n  = 114), and largemouth bass ( n  = 118). Annually, fish collection and point-source water sampling were conducted in spring, summer, and fall from both seepage and impoundment lakes. Examinations included autopsy, wet-mount cytologic assessment for ectoparasites, and histopathology. No lesions of public health concern were detected. The most common abnormalities were branchitis (261 of 429; 60.8%) and endoparasitism (312 of 429; 72.7%). Branchitis was mild in most cases (189 of 261; 72.4%) and concurrent with branchial parasitism in 175 of 261 (67%) cases. Monogeneans were the most common gill parasites but did not influence branchitis severity (Kruskal-Wallis, p  = 0.484). Using generalized ordered logistic regression, predictors of branchitis severity included fish species ( p  < 0.001), the interaction of lake or location and alkalinity ( p  < 0.001), and water temperature or season ( p  < 0.001). Endoparasites included tissue larval trematodes (metacercaria), nematodes, and cestodes (plerocercoids), enteric acanthocephalans, gastric trematodes, renal myxosporidia, biliary and gall bladder myxosporidia, enteric cestodes, and tissue microsporidia. Using generalized ordered logistic regression, variables influencing endoparasitism severity included species ( p  < 0.001), year ( p  < 0.001), chloride level ( p  = 0.009), and the interaction of year and chloride level ( p  < 0.001). Our results suggested overall good health of fish in sampled Cook County inland lakes and provide a foundation for continued monitoring of ecosystem and public health in the urban environment., Competing Interests: Declaration of conflicting interestsThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

As part of a parasitological survey, several specimens of two new monopisthocotylean species, Neotetraonchus celsomanueli sp. nov. and N. peruvianus sp. nov. (Dactylogyridea, Dactylogyridae), were collected from the gill filaments of the Peruvian sea catfish Galeichthys peruvianus (Siluriformes, Ariidae) off Puerto Pizarro, Tumbes region, Peru. Neotetraonchus celsomanueli sp. nov. is characterised by an MCO with a T-shaped distal end and an accessory piece that is ribbed and expanded proximally with a worm-shaped termination. Neotetraonchus peruvianus sp. nov. is typified by its MCO, which has a sledgehammer-shaped distal end and an accessory piece with a claw-shaped distal end. Additionally, N. peruvianus sp. nov. is characterised by its jellyfish-shaped onchium. A partial 28S rDNA sequence was obtained from N. celsomanueli sp. nov., and a phylogenetic analysis was conducted. This analysis revealed the phylogenetic position of Neotetraonchus celsomanueli sp. nov. within a clade comprising monopisthocotylean parasites of diadromous and marine ariid catfishes, including Hamatopeduncularia spp., Chauhanellus spp., Thysanotohaptor Kritsky, Shameem, Kumari & Krishnaveni, , and Neocalceostomoides spinivaginalis Lim, 1995. This finding brings the number of known Neotetraonchus species to seven and represents the first described Neotetraonchus species infecting marine catfishes from Peru.

Takifugu rubripes (T. rubripes) is a valuable commercial fish, and Cryptocaryon irritans (C. irritans) has a significant impact on its aquaculture productivity. DNA methylation is one of the earliest discovered ways of gene epigenetic modification and also an important form of modification, as well as an essential type of alteration that regulates gene expression, including immune response. To further explore the anti-infection mechanism of T. rubripes in inhibiting this disease, we determined genome-wide DNA methylation profiles in the gill of T. rubripes using whole-genome bisulfite sequencing (WGBS) and combined with RNA sequence (RNA-seq). A total of 4659 differentially methylated genes (DMGs) in the gene body and 1546 DMGs in the promoter between the infection and control group were identified. And we identified 2501 differentially expressed genes (DEGs), including 1100 upregulated and 1401 downregulated genes. After enrichment analysis, we identified DMGs and DEGs of immune-related pathways including MAPK, Wnt, ErbB, and VEGF signaling pathways, as well as node genes prkcb, myca, tp53, and map2k2a. Based on the RNA-Seq results, we plotted a network graph to demonstrate the relationship between immune pathways and functional related genes, in addition to gene methylation and expression levels. At the same time, we predicted the CpG island and transcription factor of four immune-related key genes prkcb and mapped the gene structure. These unique discoveries could be helpful in the understanding of C. irritans pathogenesis, and the candidate genes screened may serve as optimum methylation-based biomarkers that can be utilized for the correct diagnosis and therapy T. rubripes in the development of the ability to resist C. irritans infection., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Introduction: Two new dactylogyrid monogeneans, Anacanthorus cultro n. sp. and Notozothecium palometae n. sp., are described based on specimens collected from the gill filaments of Mylossoma albiscopum (Cope, 1872) (Characiformes: Serrasalmidae), a pelagic and herbivore teleost collected in the Tigre river, Loreto, Peru., Materials and Methods: Some monogeneans were stained with Gomori's trichrome and mounted in Canada Balsam to determine internal soft structures. Others were cleared in Hoyer's medium for the study of sclerotized structures. Drawings were made using a drawing tube and a microprojector., Results: Anacanthorus cultro n. sp. is characterized by the presence of a rod-shaped male copulatory organ (MCO) lacking featherlike structures, and a knife-shaped accessory piece with a submedial knob. Notozothecium palometae n. sp. can be distinguished from all congeners by its MCO with a subbasal spur and an accessory piece with inverted hammer shaped., Conclusions: This is the first data on the parasites of M. albiscopum, a popular fish in local markets. Anacanthorus cultro n. sp. is the twenty-fifth documented species of the genus in Peru, while N. palometae n. sp. represents the seventh species of the genus known to infect freshwater fish species in Peru., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

During the study of ectoparasites (Platyhelminthes) of fish in the floodplain of the Upper Paraná River - Brazil, a new species of Urocleidoides , present in the gill filaments of Hemiodus orthonops (Hemiodontidae), is described using morphological description and molecular data from the mitochondrial region of cytochrome c oxidase, subunit 1 ( COI ) and the partial region of the 28S rDNA gene. Urocleidoides luquei n. sp. differs from all its congeners by the presence of a filament that joins the accessory piece to the base of the male copulatory organ and resembles U. paradoxus and U. surianoae. Phylogenetic analyses using molecular data revealed that U. luquei n. sp. forms a paraphyletic group concerning the other Urocleidoides species. In this way, as well as contributing to the description of a new species, we seek to encourage and contribute to the increase in research using integrative taxonomy, thus making it possible to elucidate some unresolved questions about the genus Urocleidoides.

Species of Alestidae are known to be parasitised by dactylogyrid monogeneans representing three genera, Afrocleidodiscus Paperna, 1969, Annulotrema Paperna & Thurston, 1969, and Characidotrema Paperna & Thurston, 1968. The objective of the present study was to investigate the species diversity of Monopisthocotylea of African tetras from the Lower Phongolo River and floodplain in South Africa. Four new and two previously described species of Annulotrema were identified from the gills of three species of African tetras, Brycinus imberi, Hydrocynus vittatus, and Micralestes acutidens. The collected parasites were studied using two complementary approaches: morphology of hard sclerotised structures, and molecular markers using rDNA sequence data (28S rDNA, 18S rDNA, and ITS1). Three new species, Annulotrema arcum n. sp., Annulotrema caputfemoris n. sp., and Annulotrema strepsiceros n. sp., were described from B. imberi and one species, Annulotrema retortum n. sp., from M. acuditens. Two previously described species, Annulotrema pikoides Guégan, Lambert and Birgi, 1988 and A. pseudonili Kičinjaová and Řehulková, 2017, were newly recorded from H. vittatus in South Africa. Annulotrema arcum n. sp. and A. caputfemoris n. sp. share similar male copulatory organ morphologies, suggesting a close phylogenetic relationship as sister taxa. Despite weak nodal support, A. strepsiceros n. sp. shows morphological congruence with the former two species, reinforcing their molecular linkage. The present study shows a critical need for the exploration of monopisthocotylean diversity and the paucity of available molecular data of representatives from this group., (© M.L. Kičinjaová et al., published by EDP Sciences, 2024.)

Monogenea (Platyhelminthes), mainly gill and fin ectoparasites of fish, are often recognized as host specific and morphologically and ecologically diverse. These parasites exhibit high species diversity at the level of host species or individual fish specimens. Using case studies, especially those widely performed in Dactylogyrus parasitizing cyprinoid fish, this article presents current knowledge on the ecology and evolution of congeneric gill monogeneans. The important aspects of the ecology of congeneric monogeneans are highlighted, in particular: host specificity expressed at several host levels (from strict specificity to phylogenetic specificity), microhabitat specificity expressed by restricted positions on fish gills to facilitate intraspecific mating, and the link between microhabitat preference and morphological adaptation (i.e., sclerotized structures of the haptor) or reproductive isolation. From the evolutionary perspective, this study focused on the processes of the speciation and diversification of congeneric monogeneans, highlighting the role of host switch as the most prominent coevolutionary event, accompanied in some cases mostly by intrahost speciation or cospeciation, as revealed by cophylogenetic studies. Here, important knowledge on evolutionary patterns of host specificity, microhabitat specificity, and morphological adaptation is presented. Host-specific monogeneans may represent an important tool for studying the historical biogeography of their hosts. Specifically, in the case of freshwater fish hosts exhibiting disjunctive distribution, they reflect both historical and contemporary contacts. The role of host-specific congeneric monogeneans in revealing historical intercontinental and intracontinental contacts between freshwater fish is highlighted. Finally, the importance of the role of genetic coadaptation, limiting the presence of host-specific monogeneans in hybrid fish, is emphasized., (© A. Šimková et al., published by EDP Sciences, 2024.)

African cichlids are model systems for evolutionary studies and host-parasite interactions, because of their adaptive radiations and because they harbour many species of monogenean parasites with high host-specificity. Five locations were sampled in southern Lake Victoria: gill-infecting monogeneans were surveyed from 18 cichlid species belonging to this radiation superflock and two others representing two older and distantly related lineages. We found one species of Gyrodactylidae, Gyrodactylus sturmbaueri Vanhove, Snoeks, Volckaert & Huyse, 2011, and seven species of Dactylogyridae. Four are described herein: Cichlidogyrus pseudodossoui n. sp., Cichlidogyrus nyanza n. sp., Cichlidogyrus furu n. sp., and Cichlidogyrus vetusmolendarius n. sp. Another Cichlidogyrus species is reported but not formally described (low number of specimens, morphological similarity with C. furu n. sp.). Two other species are redescribed: C. bifurcatus Paperna, 1960 and C. longipenis Paperna & Thurston, 1969. Our results confirm that the monogenean fauna of Victorian littoral cichlids displays lower species richness and lower host-specificity than that of Lake Tanganyika littoral cichlids. In C. furu n. sp., hooks V are clearly longer than the others, highlighting the need to re-evaluate the current classification system that considers hook pairs III-VII as rather uniform. Some morphological features of C. bifurcatus, C. longipenis, and C. nyanza n. sp. suggest that these are closely related to congeners that infect other haplochromines. Morphological traits indicate that representatives of Cichlidogyrus colonised Lake Victoria haplochromines or their ancestors at least twice, which is in line with the Lake Victoria superflock being colonised by two cichlid tribes (Haplochromini and Oreochromini)., (© T.P. Gobbin et al., published by EDP Sciences, 2024.)

In the present study, we examined 30 individuals of introduced African cichlids, Oreochromis niloticus and Coptodon rendalli, collected in a river spring of the Pardo River, Paranapanema River basin, southeastern Brazil. Based on morphological and molecular analyses of the partial LSU rDNA gene, we identified four species of monogeneans, Cichlidogyrus tilapiae, C. thurstonae, C. mbirizei, and Scutogyrus longicornis on the gills of O. niloticus, whereas individuals of C. rendalli were infested only with C. papernastrema. This is the first record of C. mbirizei and C. papernastrema in tilapias from Brazil. The ecological consequences of the introduction of exotic species of tilapia such as O. niloticus and C. rendalli along with their monogenean parasites in a wild environment represented by a river spring are discussed. Our new molecular data on Cichlidogyrus and Scutogyrus contribute to the investigation of the phylogenetic interrelationships of these widely distributed genera of monogeneans since their species composition is still unsettled., (© M.B. Ebert et al., published by EDP Sciences, 2024.)

Pseudoplatystoma punctifer is a catfish species that occupies the first place in the statistics of fishing landings in the region of Loreto, being of economic importance in the Peruvian Amazonia. As an initiative to know the parasites present in the gills of P. punctifer from the Peruvian Amazonia, a study was carried out with fish collected in the Belén Market, in Loreto-Peru. Specimens were provided between June and October 2018 from local fishermen from the Belén Market, in Loreto-Peru and samples were processed and analyzed in the "Laboratorio de Parasitología y Sanidad Acuícola" from the "Instituto de Investigaciones de la Amazonía Peruana" (IIAP) in Iquitos, Loreto-Peru. The analyzes of the gills revealed the presence of two new species of Monogenoidea: Demidospermus aureagarciae n. sp. and D. doncellae n. sp. These species are unique among congeners by the morphology of the copulatory complex and vagina. Demidospermus aureagarciae n. sp presents a male copulatory organ as a coiled tube, with a complete counterclockwise ring, with dilated base with a developed sclerotized margin, from which a flap projects; a concave accessory piece, with a tapered and curved distal part and a saculiform vaginal vestibule, connected to the vaginal canal. Demidospermus doncellae n. sp. presents a copulatory complex that is an elongated coiled tube, with approximately three clockwise rings, with dilated base with a developed sclerotized margin, from which a flap projects; an accessory piece sheath like, and a sclerotized vagina with dextral position, with saclike vaginal vestibule, connected to an elongated canal., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

This study investigated for the first time the effectiveness of therapeutic baths with essential oil (EO) of Piper hispidum against monogeneans Anacanthorus spathulatus, Notozothecium janauachensis, Mymarothecium boegeri and Linguadactyloides brinkmanni from the gills of Colossoma macropomum, as well as the hematological and histological effects on this fish. In therapeutic baths, 100 mg/L of P. hispidum essential oil and two control groups (water from the culture tank and water from the culture tank with 70% alcohol) were exposed for 1 h/day, with intervals of 48 hours for 3 days, and three replicates each were used. Therapeutic baths with 100 mg/L of P. hispidum essential oil had an efficacy of 78.6% against monogeneans. The toxicity of this essential oil was low, since there were a few physiological and histopathological changes that did not compromise the functioning of the gills of the fish. Therefore, 100 mg/L of P. hispidum essential oil was effective for controlling monogeneans in C. macropomum, when short therapeutic baths were used without compromising the health of the exposed fish.

Purpose: The motive of the present study was to investigate incidences of myxozoan parasite infection in commercially important fishes and their characterization using morphological attributes and molecular approach., Methods: The specimens of cultured Cirrhinus mrigala were sampled and various organs were examined. The plasmodia were detected on the scales. The identification of species was based on the myxospore morphology and 18S rDNA sequence analyses. For phylogenetic analysis, maximum likelihood (ML) and Bayesian inference (BI) methods were employed. The SEM and histological studies were performed to assess the damage to the scales., Results: The infected fishes had white patches on the scales and red haemorrhagic lesions on the skin. The plasmodia of Myxobolus coriumicus n. sp. were located on the dorsal surface of the scale towards its exposed part. SEM study indicated that lepidonts were damaged in the infected scales. The myxospores were spherical in shape, 9.0-10.0 × 8.0-9.0 [Formula: see text]m in size, with two ovoid equal polar capsules 3.13-4.0 × 2.03-2.33 [Formula: see text]m in size, having 4-5 sutural edge markings at the posterior-lateral margins of the shell valves and binucleated sporoplasm. BLAST search based on 18S rDNA revealed 93.87% sequence similarity with M. rewensis, (MZ230381). The prevalence of infection was 6.3% and Scale Plasmodium Index (SPI) was 3 indicating heavy infection., Conclusion: Morpho-molecular data generated during this study enables us to conclude that the present species, M. coriumicus n. sp. infecting scales of C. mrigala is new to the science causing significant damage to the scales., (© 2023. The Author(s) under exclusive licence to Witold Stefański Institute of Parasitology, Polish Academy of Sciences.)

Background: The monogenean parasite Heterobothrium okamotoi only parasitizes the gills of Takifugu rubripes. In this study, we hypothesized that the carbohydrates contribute to high host specificity of H. okamotoi., Methods: T. rubripes, T. niphobles, T. snyderi, and T. pardalis were used for UEA I staining of the gills and an in vivo challenge test against H. okamotoi. To examine the effect of l-fucose, an in vitro detachment test was conducted using the host's gills. Additionally, fucosylated proteins were isolated from the membrane proteins of T. niphobles gills., Results: The location of l-fucoside and the infection dynamics in four species were correlated to some extent; H. okamotoi detached relatively quickly from T. niphobles possessing l-fucoside both on the surface of the gills and in certain types of cells, including mucus cells, but detached slowly from T. snyderi possessing l-fucoside in only certain types of cells, including mucus cells. Under the conditions examined, H. okamotoi exhibited minimal detachment from T. rubripes and T. pardalis, and l-fucoside was not detected. The significantly higher detachment rate of H. okamotoi from the host's gills incubated in l-fucose-containing medium compared with the controls suggests that l-fucose in the non-host gills induced detachment of H. okamotoi. Four fucosylated proteins, including mucin5AC-like, were identified as potential factors for the detachment of H. okamotoi., Conclusions: Fucosylated proteins covering the surface of non-host gills might contribute to H. okamotoi detachment., General Significance: This research shows the possible involvement of oligosaccharides in the host specificity of monogenean parasites., Competing Interests: Declaration of Competing Interest The author declares no competing interests., (Copyright © 2023. Published by Elsevier B.V.)

The host immune response in Oreochromis mossambicus during natural infection with the isopod Cymothoa eremita was investigated. The naturally infected fishes were examined for enzyme profile, viz., respiratory burst activity (RBA), myeloperoxidase activity (MPO), and expression of immune-related genes, viz., toll-like receptor 22 (TLR 22), interleukin-1β (IL-1β), tumor necrosis factor α (TNF-α), complement component (C3), chemokine (CXCa), and β-actin in tissues of various organs (buccal cavity, gills and anterior kidney). Significant reduction (P < 0.05) in RBA and MPO was observed in the parasite-infected fishes when compared to the uninfected control fishes. In the buccal cavity, the expression of the immune-related genes was significantly (P < 0.05) upregulated, whereas all the genes except IL-1β were significantly (P < 0.05) upregulated in the anterior kidney. In the case of gill tissue, the expressed genes showed a varied type of regulation. The immunological responses in O. mossambicus during isopod infection have not been investigated in detail so far, and this is the first study unveiling such insights. Hence, this study will help to improve our molecular understanding of the host-immune response to parasitic isopod infection., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Two species of Pseudodiscocotyla Yamaguti, 1965 (Monogenea: Discocotylidae) were collected from crimson jobfish Pristipomoides filamentosus (Valenciennes) (Perciformes: Lutjanidae) off Okinawa-jima island, southern Japan. Pseudodiscocotyla opakapaka is redescribed and represents the first Japanese record. A new species, Pseudodiscocotyla mikiae n. sp., differs from Ps. opakapaka in the absence of spines around the male genital pore, the shape of the vaginal pore, the presence of spines inside the vaginal pore, and the shape of the clamp. The locations of the male genital atrium and the vaginal pore in both species were similar, and the observed armament differences of the male copulatory organ are therefore presumed to establish reproductive isolation. The phylogenetic trees for the Mazocraeidea based on the partial 28S rDNA sequences were created using new sequences of Pseudodiscocotyla mikiae n. sp., and Discocotylidae formed a sister group with the species Diclidophoridae, Macrovalvitrematidae, and Plectanocotylidae. Pristipomoides filamentosus is widely distributed across the Indo-Pacific, and Pseudodiscocotyla mikiae n. sp. could share the distribution of the host., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

Objective: Proliferative gill disease (PGD) in Channel Catfish Ictalurus punctatus and hybrid catfish (Channel Catfish × Blue Catfish I. furcatus) is attributed to the myxozoan Henneguya ictaluri. Despite evidence of decreased H. ictaluri transmission and impaired parasite development in hybrid catfish, PGD still occurs in hybrid production systems. Previous metagenomic assessments of clinical PGD cases revealed numerous myxozoans within affected gill tissues in addition to H. ictaluri. The objective of this study was to investigate the development and pathologic contributions of H. ictaluri and other myxozoans in naturally and experimentally induced PGD., Methods: Henneguya species-specific in situ hybridization (ISH) assays were developed using RNAscope technology. Natural infections were sourced from diagnostic case submissions in 2019. Experimental challenges involved Channel Catfish and hybrid catfish exposed to pond water from an active PGD outbreak, and the fish were sampled at 1, 7, 10, 12, 14, 16, 18, and 20 weeks postchallenge., Result: Nine unique ISH probes were designed, targeting a diagnostic variable region of the 18S ribosomal RNA gene of select myxozoan taxa identified in clinical PGD cases. Partial validation from pure H. ictaluri, H. adiposa, H. postexilis, and H. exilis infections illustrated species-specific labeling and no cross-reactivity between different myxozoan species or the catfish hosts. After experimental challenge, mature plasmodia of H. ictaluri and H. postexilis formed in Channel Catfish but were not observed in hybrids, suggesting impaired or delayed sporogenesis in the hybridized host. These investigations also confirmed the presence of mixed infections in clinical PGD cases., Conclusion: Although H. ictaluri appears to be the primary cause of PGD, presporogonic stages of other myxozoans were also present, which may contribute to disease pathology and exacerbate respiratory compromise by further altering normal gill morphology. This work provides molecular confirmation and more resolute developmental timelines of H. ictaluri and H. postexilis in Channel Catfish and supports previous research indicating impaired or precluded H. ictaluri sporogony in hybrid catfish., (© 2023 American Fisheries Society.)

The introduction of new fish species to the aquaculture industry is essential to halt the progressive decline of natural fish stocks. The sheepshead Archosargus probatocephalus is a commercially valuable sparid fish with potential for breeding in captivity, but with limited information regarding parasitic infections that could pose a significant threat for its sustainable production. Thus, the present study aimed to study the myxozoan diversity infecting A. probatocephalus. A novel Henneguya sp. was detected forming plasmodia in the gill lamellae of specimens inhabiting the Brazilian coast, and is characterized based on morphological, histopathological, ultrastructural, molecular, and phylogenetic data. Myxospore total length was 21.3 ± 0.8 μm, with myxospore body 10.0 ± 0.5 μm long, 6.2 ± 0.3 μm wide, and 4.8 ± 0.5 μm thick. Caudal appendages were 10.3 ± 0.5 μm long and did not present any type of coating. Two pyriform polar capsules, 3.4 ± 0.3 μm long and 1.5 ± 0.2 μm wide, each containing an isofilar polar tubule with 4-5 coils. Histopathological analyses showed large intralamellar polysporic plasmodia associated with vascular congestion of the gill filament and gill lamellae, as well as epithelial hyperplasia causing partial or total fusion of gill lamellae. Maximum likelihood and Baysesian inference SSU rDNA-based phylogenetic analyses showed the novel sequence grouped within the marine clade of Henneguya spp. that mostly parasitize fishes belonging to Eupercaria incertae sedis., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Sonia Rocha reports financial support was provided by Foundation for Science and Technology (FCT). Emerson Soares reports financial support was provided by Alagoas State Research Support Foundation (FAPEAL)., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Invasive Nile tilapias negatively impact native tilapia species through hybridisation and competition. However, the co-introduction of parasites with Nile tilapia, and subsequent changes in parasite communities, are scarcely documented. Monogeneans are known pathogens of cultured Nile tilapia, although little is known about their fate once Nile tilapias establish in new ecosystems. We investigate the parasitological consequences of Nile tilapia introduction on native tilapias in basins in Cameroon, the Democratic Republic of the Congo (DRC), and Zimbabwe, focusing on ectoparasitic dactylogyrids (Monogenea). Using the mitochondrial cytochrome oxidase c subunit I (COI) and nuclear 18S-internal transcribed spacer 1 (18S-ITS1) rDNA region of 128 and 166 worms, respectively, we evaluated transmission of several dactylogyrid species. Parasite spillover from Nile tilapia was detected for Cichlidogyrus tilapiae to Coptodon guineensis in Cameroon, Cichlidogyrus thurstonae to Oreochromis macrochir in the DRC, and Cichlidogyrus halli and C. tilapiae to Coptodon rendalli in Zimbabwe. Parasite spillback to Nile tilapia was detected for Cichlidogyrus papernastrema and Scutogyrus gravivaginus from Tilapia sparrmanii and Cichlidogyrus dossoui from C. rendalli or T. sparrmanii in the DRC, and Cichlidogyrus chloeae from Oreochromis cf. mortimeri and S. gravivaginus from O. macrochir in Zimbabwe. 'Hidden' transmissions (i.e. transmission of certain parasite lineages of species that are naturally present on both alien and native hosts) were detected for C. tilapiae and Scutogyrus longicornis between Nile tilapia and Oreochromis aureus and C. tilapiae between Nile tilapia and Oreochromis mweruensis in the DRC, and Cichlidogyrus sclerosus and C. tilapiae between Nile tilapia and O. cf. mortimeri in Zimbabwe. A high density of Nile tilapia occurring together with native tilapias, and the broad host range and/or environmental tolerance of the transmitted parasites, are proposed as factors behind parasite transmission through ecological fitting. However, continuous monitoring and the inclusion of environmental variables are necessary to understand the long-term consequences of these transmissions on native tilapias and to elucidate other underlying factors influencing these transmissions., (Copyright © 2023 Australian Society for Parasitology. Published by Elsevier Ltd. All rights reserved.)

With growing scale of intensive fish cultivation, the risk of parasite infection in commercial fish is increased. Precisely identifying and characterizing the parasites that infect the farmed fish is critical to understanding the dynamics of their communities. Here, two species of Myxobolus were identified in farmed yellow catfish Tachysurus fulvidraco (Richardson) in China. Myxobolus distalisensis n. sp. developed plasmodia in the gill filaments, with oval to elliptical myxospores measuring 11.3 ± 0.6 (10.4-12.6) × 8.1 ± 0.3 (7.5-8.6) × 5.5 ± 0.2 (5.2-5.8) μm. Two pyriform polar capsules of equal size were measured 5.3 ± 0.4 (4.5-6.3) × 2.7 ± 0.1 (2.3-3) μm. Myxobolus voremkhai (Akhmerov, 1960) Landsberg and Lom, 1991 developed plasmodia in the gill arch and had a myxospore morphology similar to the conspecific isolates described in previous studies. The consensus sequences of M. distalisensis was remarkably distinct from those deposited in the GenBank, with exception of whereas M. voremkhai showing 99.84% identity. The genetic data on both isolates differed considerably from each other, revealing only 86.96% molecular identity. Histologically, M. distalisensis resided in the filament cartilage, and the aggressive proliferation of the sporogenic stages led to lytic cartilage corrosion. In contrast, plasmodia of M. voremkhai grossly observed at the base of the gill filament were embedded by the connective tissue in the gills arch. Phylogenetically, both isolates were separately placed in different subclades, indicating difference in their evolutionary history. Besides, the taxon under the family Myxobolidae was demonstrated non-monophyletic origins, and parasite radiation largely followed their host affinity., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)