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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.)

AbstractIndirect genetic effects (IGEs) exist when there is heritable variation in one organism's ability to alter a second organism's traits. For example, parasites have antigens that can induce a host immune response, as well as disparate strategies to evade or suppress host immunity; among-parasite genetic variation in these antigens generates among-host variation in immune traits. Here, we experimentally show that the cestode parasite Schistocephalus solidus exerts an IGE on an immune trait (peritoneal fibrosis) in its threespine stickleback host: stickleback developed strong fibrosis after exposure to some parasite genotypes but not others. A complication arises during coinfection, when two or more parasite genotypes may impose conflicting IGEs on the same host trait. What parasite-controlled trait will the host express? Will the host trait reflect the more immune-stimulatory parasite genotype or the more immune-evasive genotype? These alternatives can be quantified by estimating the dominance coefficient, as if a coinfected host were a heterozygote. We experimentally estimated the dominance of S. solidus IGEs by coinjecting antigens from different parasite genotypes. Contrary to our a priori hypotheses, coinjected antigens induced an overdominant effect, stronger than either parasite's antigens alone. We present a mathematical model showing that the value of this IGE dominance is biologically important, affecting the evolutionary dynamics of parasites in a density- and frequency-dependent manner. The model indicates that overdominance would be detrimental to immigrants when resident prevalence is high. This combination of experimental data and modeling provides an example of a parasite IGE on host traits and the evolutionary significance of IGE dominance.

This study aimed to perform in vitro antiparasitic and antimicrobial tests with the essential oil (EO) of Schinus terebinthifolius against of fish and shrimp. The chemical composition of the EO of S. terebinthifolius was determined by gas chromatography. For the antiparasitic test, the protozoan Epistylis sp. obtained from parasitized Oreochromis niloticus was used, and exposed to different concentrations of EO (2%, 1%, 0.5%, 0.25%), and control with 1% grain alcohol. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) test with EO of S. terebinthifolius evaluated the antimicrobial potential, with serial dilutions starting at 2% and control with 1% grain alcohol, using the strains of Aeromonas hydrophila (2.2 × 10 8  CFU mL -1 ), Edwardsiella tarda, Vibrio parahaemolyticus, V. harveyi, and V. alginolyticus (2.0 × 10 8  CFU mL -1 ). Chemical analysis revealed that the major EO compounds of S. terebinthifolius were δ-3-Carene (56.00%) and α-Pinene (16.89%). In the antiparasitic test, the concentration of 2% EO showed 100% efficacy against Epistylis sp. within 5 min. In the antimicrobial tests, the concentration of 2% EO was effective against all bacteria tested. The EO of S. terebinthifolius demonstrated antiparasitic and antimicrobial activity at a concentration of 2%, standing out as an alternative to conventional antibiotics., (© 2024 John Wiley & Sons Ltd.)

This study investigated the in vitro antimicrobial and anthelmintic effect of copper nanoparticles (CuNPs) against the bacterium Aeromonas hydrophila, the monogeneans Dactylogyrus minutus, Dactylogyrus extensus, Gyrodactylus cyprini, and the cestode Schyzocotyle acheilognathi, as well as their toxicity to Cyprinus carpio Koi. In the antimicrobial in vitro test, the inhibition zone method and minimum inhibitory concentration (MIC) were performed. In order to determine the time and efficacy of monogenean parasite mortality, the parasites were exposed to CuNP concentrations of 20, 50, 100, 150, 200, and 300 mg L -1 , and a control group with tank water and one with copper sulphate pentahydrate (CuSO 4 . 5 H 2 O) at a concentration of 0.3 mg L -1 , performed in triplicate. The parasites were observed every 10 min for 300 min, and mortality was recorded. For the cestodes, parasites were immersed in CuNP concentrations of 50, 100, 150, and 300 mg L -1 . At the end of the in vitro tests, the anthelmintic efficacy of each treatment was calculated. To assess the tolerance and toxicity in fish, they were exposed to CuNP concentrations of 0.6, 1.25, 2.5, 5, 10, 20, and 50 mg L -1 for 12 h. The MIC demonstrated that CuNPs effectively inhibited the growth of A. hydrophila up to a dilution of 12,500 mg L -1 and showed an inhibition zone of 14.0 ± 1.6 mm for CuNPs. The results of anthelmintic activity showed a dose-dependent effect of concentration for both groups of parasites, with the most effective concentration being 300 mg L -1 in 120 min. In the toxicity test, the carps showed tolerance to lower concentrations. The study indicated that CuNPs were effective against the studied pathogens. However, it proved to be toxic to fish at high concentrations. The use of low concentrations is recommended still requires further investigation., (© 2024 John Wiley & Sons Ltd.)

Aim: Many fish species can harbour a wide range of pathogenic agents in their tissues. Of many pathogens, the parasitic nematode of genus Contracaecum, which resides in the tissues of fish species, can results in fish-borne infections in humans. This study was planned to assess consumers' awareness of fish-borne zoonoses in the fishing sites of Lake Chamo, Arba Minch, Ethiopia. The study was also aimed at demonstrating the zoonotic nematode, Contracaecum parasites in the Oreochromis niloticus and Lates niloticus fishes collected from Lake Chamo, Arba Minch, Ethiopia., Methods and Results: Assessment of awareness about fish-borne zoonoses was conducted in randomly selected participants (n = 162) using face-to-face interviews via a structured and semi-structured questionnaire. Besides, 70 fishes (O. niloticus = 35 and L. niloticus = 35) were examined for the presence of larva of Contracaecum and other anisakid genera through standard dissection, pepsin-hydrochloric acid digestion and microscopic observation. Consumers have inadequate awareness about fish-borne zoonoses based on the answers they provided to the questions. The majority of respondents (82%) consume raw fish in the area. Of these, a significantly higher proportion were male (p < 0.001), completed their elementary or high school (p = 0.004), Orthodox Christian (p = 0.044), fishermen (p < 0.001) and participants without previous information about fish-borne zoonoses (p < 0.001). Overall, of examined fishes (n = 70), n = 15 (21.4%, 95% CI, 12.8-33.2) were infected with Contracaecum larva. A significant (p = 0.028) higher infection prevalence was noted in L. niloticus (34.3%, 95% CI, 19.7-52.3) compared to O. niloticus (8.6%, 95% CI, 2.2-24.2). A unit gram addition in the total weight of fish would significantly raise the risk of Contracaecum infection by 1% (p < 0.001)., Conclusions: The presence of Contracaecum, a zoonotic nematode in the fishes, which are often preferred by consumers for raw dishes, designates a high risk of possible fish-borne infections in the area. Thus, providing education and training for fishermen, visitors of the area, and local people who visit the area for fish consumption, it is inevitably important to minimize the risk. Furthermore, health workers should suspect fish-borne infections, such as anisakidosis in patients who have a history of raw fish consumption in Arba Minch, Ethiopia., (© 2024 Wiley‐VCH GmbH. Published by John Wiley & Sons Ltd.)

Species-level delineation of digenetic trematodes is complex and can be best achieved by integrative taxonomy using both genetic characterisation and morphological analysis. Two new Bucephalidae species of the genus Rhipidocotyle Diesing, 1858 are described here based on specimens collected from the intestine of Sphyraena putnamae Jordan & Seale following this approach. Adults of R. siphonyaka n. sp. and R. nolwe n. sp. possess tentacles and a tegument with scales. They are distinguished from their congeners by the arrangement of the digestive structures, the extent of the uterus relative to vitelline fields, and the arrangement of the reproductive structures. Rhipidocotyle siphonyaka n. sp. differs from R. nolwe n. sp. in having the pharynx and mouth positioned in the pre-uterine field, tandem testes, longer body length, and shorter pre-vitelline and post-testicular distance. Rhipidocotyle siphonyaka n. sp. differs from its congeners in having a tube-like intestinal caecum, pharynx and mouth opening positioned in the pre-vitelline field. Rhipidocotyle nolwe n. sp. appears to be similar, morphologically and morphometrically, to Rhipidocotyle khalili (Nagaty, 1937). Despite their similarities, R. nolwe n. sp. has a shorter body length and egg size. Moreover, the molecular analysis of 28S and ITS rDNA fragments indicate that R. siphonyaka n. sp. and R. nolwe n. sp. are closely related phylogenetically but distinct from one another and other Bucephalidae for which molecular data are available.

Two new species of the genus Allocreadium were isolated from the intestines of the Lake minnow Rhynchocypris percnura caught in the backwater of the Komissarovka River in the South of the Russian Far East. The morphology of A. anastasii n. sp. corresponds to that of Allocreadium sp. from Lake Khar (Mongolia) and Allocreadium sp. Belous, 1952 from the Primorsky region of Russia except for the preacetabular anterior border of the vitelline follicles in A. anastasii n. sp. from the Komissarovka River vs. at anterior half of ventral sucker in Allocreadium sp. Genetic analysis revealed the identity of A. anastasii n. sp. to Allocreadium sp. 1 from the Nezhinka River and Lake Khar. Allocreadium macrolecithum n. sp. was differentiated from Palaearctic Allocreadium spp. by having the following features: respectively large vitelline follicles extending from posterior extremity to anterior margin of the ventral sucker; relatively short caeca reaching the border of middle and posterior thirds of hindbody; and small testes in the middle of hindbody. Interspecific genetic p-distances between Allocreadium spp. were 0.16-7.23% in 28S gene and 18.62-31.54% in Cox1 mtDNA gene. In the phylogenetic tree reconstructed with Maximum parsimony and Bayesian Inference methods, A. anastasii n. sp. and A. macrolecithum n. sp. were nested into different species groups of the genus Allocreadium - sister to A. khankaiense and A. bursense , respectively. Modified dichotomous keys were prepared for 31 Palaearctic species of Allocreadium including A. crassum , A. dogieli , A. papilligerum , A. bursense , A. anastasii n. sp., and A. macrolecithum n. sp.

Fish-borne zoonotic trematodes (FBZTs) pose significant health risks and economic challenges worldwide. This study investigated the prevalence of encysted metacercariae (EMCs) in Nile tilapia (Oreochromis niloticus) from two Egyptian governorates and evaluated the antiparasitic efficacy of chitosan, silver, and selenium nanoparticles against these parasites. A cross-sectional analysis of 453 O. niloticus specimens revealed an overall EMC prevalence of 40.8%, with infection rates of 34.11% in Giza and 49.5% in Dakahlia. Clinostomid and Prohemistomid metacercariae were the most common, with mixed infections observed. Transmission electron microscopy characterized the synthesized nanoparticles, showing average diameters of 9.6-18.7 nm for chitosan, 13.2-19.8 nm for selenium, and 11.7-15.1 nm for silver nanoparticles. In vitro antiparasitic assays demonstrated varying efficacies among the nanoparticles. Against Clinostomum spp. metacercariae, chitosan nanoparticles showed the highest potency, achieving LC50 at 66 μg/ml after 30 min and LC90 at 100 μg/ml after 120 min. For Prohemistomum vivax EMCs, chitosan nanoparticles exhibited superior efficacy, achieving LC50 at 8 μg/ml after 1 h and LC90 at 16 μg/ml after 2 h. Silver and selenium nanoparticles showed lower efficacy for both parasite species. Scanning electron microscopy revealed significant ultrastructural damage to the parasite tegument following nanoparticle exposure, including disappearance of transverse ridges, integument shrinkage, and formation of blebs. This study provided valuable insights into the prevalence of FBZTs in Egyptian Nile tilapia and demonstrated the potential of nanoparticles, particularly chitosan, as effective antiparasitic agents. These findings pave the way for developing novel, targeted strategies to control fish-borne zoonotic trematodes, potentially reducing their impact on public health and aquaculture economies., (© 2024. The Author(s).)

The trematode family Cyathocotylidae infects various hosts worldwide, including birds, mammals, reptiles, and fish. However, the lack of molecular data from adult worms hinders phylogenetic, epidemiological, and host association studies. This study aims to identify the common cyathocotylid trematodes infecting African catfish in Egypt using morphological and molecular evidence. Out of 142 Clarias gariepinus, 123 fish (86.6%) harbored cyathocotylid metacercariae, with a mean metacercarial intensity of 201 ± 38.5/g. Cyathocotylid metacercariae prevalence gradually rose as host size increased. Although there was no significant difference between groups, larger fish had a higher mean metacercarial intensity. The prevalence and intensity were unrelated to the fish gender. Histopathological examination of metacercariae-infected catfish revealed varying degrees of degenerative changes, including intermuscular edema leading to muscle fiber dispersion and atrophy, involving 11% to over 81% of muscle sections. We identified three cyathocotylid metacercariae and eight cyathocotylid adult species from experimental infection using morphometric and molecular data, including internal transcribed spacer (ITS) and/or mitochondrial cytochrome c oxidase subunit 1 (cox1) sequences. We determined the phylogenetic position of these cyathocotylid samples. The ITS sequence analysis linked the isolated Cyathocotylidae sp. 1 and 2 metacercariae to Prohemistomum vivax adults. Mesostephanus appendiculatoides and Paracoenogonimus ovatus were reported for the first time in Egypt. These findings may provide valuable genetic data for future molecular epidemiological and phylogenetic studies of cyathocotylid trematodes., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

For many years, parasite ecologists have debated the relative importance of phylogeny and ecology as drivers of parasite community structure. Here, we address this issue using data on the metazoan ectoparasite communities of different flatfish species. Twenty species of flatfish were collected along the continental shelf of the Southern Gulf of Mexico and examined for ectoparasites. Eight flatfish species were parasitized by at least one ectoparasite species. In total, 326 ectoparasites, representing 11 species (4 monogeneans, 4 copepods, 1 isopod, 1 branchiurid, and 1 leech) were removed from 1622 hosts examined. The highest prevalence (37.5%) occurred in Bomolochus sp1 from Trinectes maculatus, while the lower (0.1%) for Argulus sp., Gnathia sp. and Trachellobdella lubrica from Cyclopsetta chittendeni. Changes in the ectoparasite community structure per host species and region were evaluated using a Permutational Multivariate Analysis of Variance and represented by a multidimensional scaling analysis. Significant differences in the parasite species composition among regions and hosts were detected, but no significant interaction between regions and hosts occurred. A multivariate pairwise t-test detected significant differences in the parasite infracommunities between the Yucatan Shelf and the other two regions; in addition, significant differences were detected between C. chittendeni and the Syacium species as well as between Ancylopsetta dilecta and Syacium papillosum. In this case, there is no relationship between the patterns of ectoparasitic community structure and the inherent phylogenetic affinity of the hosts; instead, the variations in ectoparasitic communities are determined by a regional ecological component., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Soler-Jiménez 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.)

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.)

Multivalvulidan myxosporeans (Multivalvulida) of the genera Unicapsula Davis, 1924 and Kudoa Meglitsch, 1947 are mostly causative agents of latent and imperceptible infection in marine fishes. However, they are sometimes incriminated in causing post-mortem myoliquefaction or unsightly cyst formation in commercial fish. Despite the great commercial impacts of multivalvulidan infection, the biodiversity, host range and epidemiology of multivalvulidan species remain to be explored further, including infection of alternative annelid hosts. Therefore, this study aimed to identify multivalvulidan species and their host and/or distribution records in commercial fishes in China. Multivalvulidan infection was detected in ten commercial fish species of seven families from the South and East China Seas (Northwest Pacific Ocean) and the Eastern Central Atlantic Ocean (an imported Dagetichthys lusitanicus [de Brito Capello]). Based on morphological and molecular-genetic analyses of their small and large subunit of ribosomal RNA genes, five new host and/or geographical distribution records for five fish species are presented, and three new species in five fish species are described, namely Kudoa neoscomberomori sp. n. in Scomberomorus commerson (Lacépède); Kudoa pilosa sp. n. in Helicolenus hilgendorfi (Döderlein) (type host) and Sebastiscus tertius (Barsukov et Chen); and Kudoa tumidisporica sp. n. in Photopectoralis bindus (Valenciennes) (type host) and Nuchequula nuchalis (Temminck et Schlegel). This study provides new data on multivalvulidan diversity in the ocean ecosystem.

Infectious diseases stem from disrupted interactions among hosts, parasites, and the environment. Both abiotic and biotic factors can influence infection outcomes by shaping the abundance of a parasite's infective stages, as well as the host's ability to fight infection. However, disentangling these mechanisms within natural ecosystems remains challenging. Here, combining environmental DNA analysis and niche modelling at a regional scale, we uncovered the biotic and abiotic drivers of an infectious disease of salmonid fish, triggered by the parasite Tetracapsuloides bryosalmonae. We found that the occurrence and abundance of the parasite in the water-i.e., the propagule pressure- were mainly correlated to the abundances of its two primary hosts, the bryozoan Fredericella sultana and the fish Salmo trutta, but poorly to local abiotic environmental stressors. In contrast, the occurrence and abundance of parasites within fish hosts-i.e., proxies for disease emergence-were closely linked to environmental stressors (water temperature, agricultural activities, dams), and to a lesser extent to parasite propagule pressure. These results suggest that pathogen distribution alone cannot predict the risk of disease in wildlife, and that local anthropogenic stressors may play a pivotal role in disease emergence among wild host populations, likely by modulating the hosts' immune response. Our study sheds light on the intricate interplay between biotic and abiotic factors in shaping pathogen distribution and raises concerns about the effects of global change on pathogen emergence., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Simon Blanchet reports financial support was provided by French Biodiversity Office. If there are other authors, they 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.)

Sleep is a complex and conserved biological process that affects several body functions and behaviors. Evidence suggests that there is a reciprocal interaction between sleep and immunity. For instance, fragmented sleep can increase the probability of parasitic infections and reduce the ability to fight infections. Moreover, viral and bacterial infections alter the sleep patterns of infected individuals. However, the effects of macro-parasitic infections on sleep remain largely unknown, and measuring sleep in non-model organisms remains challenging. In this study, we investigated whether macro-parasite infections could alter sleep-like behavior of their hosts. We experimentally infected three-spined sticklebacks (Gasterosteus aculeatus), a freshwater fish, with the tapeworm Schistocephalus solidus and used a hidden Markov model to characterize sleep-like behavior in sticklebacks. One to four days after parasite exposure, infected fish showed no difference in sleep-like behavior compared with non-exposed fish, and fish that were exposed-but-not-infected only showed a slight reduction in sleep-like behavior during daytime. Twenty-nine to 32 days after exposure, infected fish showed more sleep-like behavior than control fish, while exposed-but-not-infected fish showed overall less sleep-like behavior. Using brain transcriptomics, we identified immune- and sleep-associated genes that potentially underlie the observed behavioral changes. These results provide insights into the complex association between macro-parasite infection, immunity, and sleep in fish and may thus contribute to a better understanding of reciprocal interactions between sleep and immunity., (© 2024. The Author(s).)

The Amazon is the largest river basin in the world and it is home to the greatest diversity of freshwater fish in the world. Mesonauta festivus is a cichlid popularly known as flag cichlid, widely distributed throughout South America. The diversity of parasites in fish from the Amazon region is still underestimated, due to the high fishes diversity. The Myxozoa class has a universal distribution, with some specimens being pathogenic to some fish. The aim of this work was to describe a new species of Hoferellus in M. festivus. The fish were collected in the lake region, municipality of Tartarugalzinho, in the state of Amapá, Brazil. The new species was found parasitizing the urinary bladder of M. festivus. Spores were 11.5 ±1.1 (10.4-12.6) µm long and 10.9 ±1 (9.9-11.9) µm wide, and polar capsules were equally sized, measuring 4.9 ±0.5 (4.4-5.4) µm long and 3.4 ±0.9 (2.5-4.3) µm wide, with a pyriform shape, convergent with the apical region of the spore. The polar filament was wound with 5 to 6 turns. Morphological, morphometric, molecular and phylogenetic analysis proved that it is a new species of Hoferellus in the Amazon region.

Myxozoa is a class of the Phylum Cnidaria made up of endoparasites from aquatic habitats. The genus Ceratomyxa preferentially infects marine fish, with the gallbladder being the main site parasitized. This study aimed to describe a new species of Ceratomyxa found in this organ in Boulengerella cuvieri using morphological, morphometric characterization and phylogenetic analysis of 18S rDNA gene sequences. Specimens of B. cuvieri were collected, anesthetized, desensitized and biometric measurements were performed. The organs were analyzed under a stereomicroscope and fragments of internal organs were extracted for light microscopy analysis, preserved in 80% ethanol for 18S rDNA gene analysis and fixed in Davidson solution for histological processing. Free spores of Ceratomyxa were observed in the gallbladder, in plasmodia with wave-like movements, with the following dimensions: spore width (24.5 ± 0.4) µm, spore length (5.2 ± 0.3) µm, polar capsule width (1.8 ± 0.2) µm, polar capsule length (2.1 ± 0.3) µm, number of polar tubule turns (4-5) and 100% prevalence. Phylogenetic analysis confirmed that Ceratomyxa matosi n. sp. is a new species, grouped with other freshwater Ceratomyxa species from the Amazon, representing the second description of species of this genus in the state of Amapá.

This study aimed to conduct a multidisciplinary investigation integrating detailed morphology, molecular characterization, water parameters, histopathology alteration, and the trials of treatment of Clinostomum spp. In this study, 300 Nile tilapia (Oreochromis niloticus) were collected from the farmed and wild Nile River at Al Bahr Al Aazam, Giza Governorate to assess Clinostomid infection prevalence. Fish and water samples were collected from private fish farms, and water drains at Dakahlia, and Giza, Egypt. Analysis of the water revealed inadequate water quality, particularly in the fish farms. Snails and piscivorous birds were abundant at fish collection sites. The recovered Clinostomid MCs morphological characteristics and COI gene sequence analysis identified them as Clinostomum complanatum, C. phalacrocoracis, and Euclinostomum heterostomum. Clinostomid MCs disturbed the fish's hematological and biochemical blood parameters. Bath treatment of parasitized fish with praziquantel (2 mg/L for 24 h) revealed a significant reduction in the number of vital MCs vs. infected fish (non-treated). Praziquantel (PZQ) is an effective and safe therapy for controlling Clinostomid infections affecting farmed Nile tilapia. The current findings indicate a link between poor environmental conditions and Clinostomum infections in tilapia. The study highlights the impacts of Clinostomid MCs on fish health and recommends bath treatment with PZQ as an efficient control method for these dangerous parasites to protect human and fish health., (© 2024. The Author(s).)

This study investigated the role of host traits, habitat, and sampling season on the prevalence and intensity of parasites in three species of platycephalid fishes. Three host species sampled were dusky flathead (Platycephalus fuscus, n = 3), blue-spotted flathead (Platycephalus caeruleopunctatus, n = 38), and tiger flathead (Platycephalus richardsoni, n = 59). A total of 14 metazoan parasite species were collected over 15 months, between July 2020 and September 2021. The parasites found included a chondracanthid copepod, adult hemiuroidean trematodes, cestode plerocercoids, larval and adult acanthocephalans, larval and adult nematodes, and an unknown species of helminth. General linear models were used to assess the relationship between host traits and sampling season with parasite infection intensity. The infection intensity of an unidentified plerocercoid species in P. caeruleopunctatus was found to be significantly associated with both sampling season and the interaction of host mass with sex. In P. richardsoni the infection intensity of the acanthocephalan, Corynosoma sp. was found to correlate with sampling season. The highest richness of parasite taxa was recorded from P. richardsoni, which may be due to the wide depth range of P. richardsoni, coupled with its generalist diet., (© 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.

The structure of the envelopes (capsule and cyst) surrounding metacercariae of Stephanostomum baccatum (Nicoll, 1907) in the second intermediate host, the yellowfin sole Limanda aspera (Pallas 1814), is examined with the methods of light and transmission electron microscopy. The cyst, presumably formed by secretions of the metacercarial tegument, consists of 2 layers: the outer, very thin layer of an electron-dense, finely granular substance and the inner layer composed of loose material of a moderate electron density that includes dense bodies varying in size, shape, and localization. The capsule, formed by the host's cells, is also organized into 2 distinct layers. The inner layer of the capsule is loose, consisting of evenly spaced debris of degenerated cells and lipid droplets with inclusions of intact macrophages between them. The outer layer of the capsule consists of parallel rows of cells arranged around the parasite, with fibroblasts and macrophages being dominant types and granulocytes and lymphocytes found in smaller numbers. Aggregations of collagen fibers are located in narrow spaces between the cells. The number of lipid droplets in the outer layer is significantly smaller than in the inner layer. The capsules formed around the examined trematodes have several structural features that distinguish them from those of S. baccatum and Stephanostomum sp. metacercariae recovered from other fishes of the family Pleuronectidae. The major morphological features of such capsules are the lack of epithelioid or giant multinucleated cells and the presence of numerous lipid droplets. Investigating the structural details of the envelopes surrounding metacercariae in trematodes, as well as other helminths, contributes to our scientific understanding of parasite biology, which can, in turn, have broader implications for understanding host-parasite interactions and evolutionary biology., (© American Society of Parasitologists 2024.)

In order to know whether there is a risk of anisakiasis (or anisakidosis) by consumption of fish of the genus Mullus from the western Mediterranean Sea, which are appreciated for their quality, an epidemiological survey was carried out to evaluate the occurrence of zoonotic or potentially zoonotic nematodes in M. barbatus and M. surmuletus. Although the presence of the third larval stage (L3) of anisakids (Anisakis and Contracaecum) has been previously described in these fish, the results showed the absence of anisakids and the presence, never in muscle, of L3 and L4 of raphidascaridids of the genus Hysterothylacium, molecularly identified as H. fabri. Phylogenetic analysis groups them into the Mediterranean Sea clade, far from individuals isolated in the Pacific Ocean. Prevalence was slightly higher, but not significant, in M. barbatus versus M. surmuletus (72.3% vs 60.0%), but mean intensity (MI) and mean abundance (MA) parameters were approximately twice as high in M. barbatus as in M. surmuletus (MI 5.8 vs 2.8, p = .001; MA 4.2 vs 1.7, p < .001). The presence of the parasite seems to have different effects on these two sympatric species. In M. barbatus it seems to affect their growth, as it appreciably reduces the value of allometry coefficient in infected fish (2.78 vs. 2.18). On the other hand, in M. surmuletus the infection significantly (p < .04) affects the Fulton's condition factor, an indicator of the health status of the fish. It can be concluded that the ingestion of these fish by the people poses negligible risk of anisakiasis, but the consumer should continue to be urged to follow the rules of prevention against this illness., (© 2024 The Author(s). Journal of Fish Diseases published by John Wiley & Sons Ltd.)

Alternatives to conventional chemical treatments for parasitic diseases in fish are needed. Microalgal-sourced fatty acid ethyl esters (FAEEs) have shown an antiparasitic effect against Gyrodactylus turnbulli infection in guppies. Here, we tested a range of commercial FAEEs of various carbon chain lengths and unsaturation levels against two fish parasites. Guppies and barramundi infected with G. turnbulli and Trichodina sp., respectively, were used. The most effective FAEE, after excluding those toxic to fish, was ethyl laurate (12:0). For both parasites, the LD50 was 18.75 μM within 250 min of incubation. Ethyl eicosapentaenoate (20:5n3) was the next most effective FAEE against G. turnbulli, and dihomo-γ-linolenic acid ethyl ester (20:3n6) and ethyl α-linolenate (18:3n3) were the next most effective against Trichodina sp. In addition, FAEEs prepared from the microalga Phaeodactylum tricornutum residue, after fucoxanthin extraction, were examined against Trichodina sp. infection in barramundi for the first time. LD85 and LD100 was achieved at 2.5 and 5 μL mL -1 of the FAEE preparation, respectively. In vivo, immersion of infected barramundi in 1.25 μL mL -1 of this preparation for 24 h reduced infection prevalence from 100% to 53% and was non-toxic to fish., (© 2024 The Author(s). Journal of Fish Diseases published by John Wiley & Sons Ltd.)

Ichthyophthirius multifiliis is a parasite that poses a considerable threat to aquaculture and the ornamental fish industry, but with limited effective treatment options available. This study employed RT-qPCR to detect and analyze the expression changes of partial toll-like receptor (TLR) genes (TLR1 and TLR21), adapter protein and signal transduction molecule genes (MyD88, TRIF, NF-κB, IRAK4, and IRF3), and cytokines (IL-6, IL-8, IL-13, CXC-α and CXCR1), as well as complement C3, in the skin, gill, fin, liver, head kidney and spleen of Rhinogobio ventralis under different infection conditions. Additionally, tissue sections and scanning electron microscopy were utilized to observe the pathological changes in the gills and fins of R. ventralis after infection with I. multifiliis. The expression patterns of TLR-related DEGs (differentially expressed genes) in diseased wild fish were analyzed, revealing upregulation of TLR1, TLR21, MyD88, NF-κB, IRAK4, TRIF, IRF3, IL-6, IL-8, IL-13, CXC-α, CXCR1, and C3 genes in various tissues, indicating that these genes may be involved in the immune response of R. ventralis to I. multifiliis infection. To further analyze the gene expression of sampled from the field, an artificial infection model of R. ventralis was established under laboratory conditions, with additional sampling from the skin and fins. These genes continued to show varying degrees of upregulation, but the results were not entirely consistent with those from Wudongde samples, which may be due to the more complex environment in the wild or differences in the degree of I. multifiliis infection in wild fish. The infection of I. multifiliis caused severe damage to the gills and fins of R. ventralis, characterized by extensive secretions on the gill and fin surfaces, with the presence of attached I. multifiliis trophonts, including damage and loss of gill filaments, swollen gill lamellae, and deformed gill plates, as well as cell proliferation and necrosis of gill epithelial cells. This study sheds light on the role of the TLR signaling pathway in resisting I. multifiliis infection and its associated histopathological changes in R. ventralis, providing valuable insights for the prevention and treatment of I. multifiliis infection in R. ventralis., 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 Ltd. All rights reserved.)

The aquaculture industry is hindered by various factors. One of the most noticeable factors is infection by parasites and pathogens. Argulus stands out as a prominent and economically significant ectoparasite in freshwater aquaculture. Argulus infestation causes severe immunomodulatory effects on its hosts by promoting argulosis, causing inflammation, extensive tissue damage, and death. Indian aquaculture sector faced a loss of 62.5 million USD due to Argulus infection. However, current control methods, such as pesticides, cause serious environmental damage. Herbal treatment methods are ineffective and have limitations. Hence, a more efficient and cost-effective control method is needed. In recent years, vaccine development has emerged as a promising avenue of research. Understanding the effect of the host-parasite relationship in the host immune system is essential to develop strategies for prevention, control, and management of argulosis. These interactions provide insights into the co-evolutionary dynamics between hosts and parasites. This review provides an overview of the current knowledge on the host-searching behaviour of Argulus, host-parasite interaction and control strategies. This review also highlights the need for further research and the development of sustainable control measures for Argulus infection., 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 Ltd. All rights reserved.)

A new genus, Cordicestus, is proposed to accommodate proteocephalid tapeworms parasitising gars (Lepisosteiformes: Lepisosteidae) in North and Central America that were previously placed in the polyphyletic genus Proteocephalus Weinland, 1858. The new genus differs from other proteocephalid genera by the particular morphology of the scolex, which is small, protrudes apically but has no apical organ, and bears flat, heart-shaped (= cordis) suckers. In addition, the species of the new genus have an elongated cirrus sac with an almost straight internal vas deferens and wide, sinuous ventral osmoregulatory canals with secondary canals directed outwards. The type species of the new genus, Cordicestus singularis (La Rue, 1911) n. comb., is redescribed based on new material from the shortnose gar, Lepisosteus platostomus Rafinesque (type host), and the spotted gar, L. oculatus Winchell, in the United States. Cordicestus rafaeli n. sp. is described from the tropical gar, Atractosteus tropicus Gill, in Mexico. The new species differs from its relatives primarily by the presence of craspedote proglottids (acraspedote in other species) and some biometric features. All species of Cordicestus are revised, including unidentified specimens from A. tropicus and the Cuban gar A. tristoechus (Bloch and Schneider) in Nicaragua and Cuba, respectively, which may be new species, and a key to the identification of these taxa is provided. Molecular data available for two nominal species of the new genus indicate the possible existence of another species of Cordicestus in Lepisosteus in the USA., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Parasitological studies of long-term inter-annual variations provide more precise and reliable information about the biological structure of fish parasite communities, and constitute a reference data base for future studies. A total of 1103 blue sea catfish Ariopsis guatemalensis from a tropical eutrophic coastal lagoon were examined for parasites over a 22-year period (from May 2000 to October 2022), to test the hypothesis that parasite communities of this host, should exhibit greater variations in their structure and species composition mainly over long-term periods. Three species of monoxenous (single-host life cycle), and nine of heteroxenous (multi-host life cycle) parasites were identified. The results indicated that parasite species composition of this catfish has remained stable over a 22-years period. However, the community structure has registered notable changes over periods of several years, mainly due to the replacement of the numerically dominant species. Temporal variations in the infection dynamics of component parasite species, were possibly caused by a combination of biotic and abiotic factors, influenced by the seasonal dry/rainy cycle, which can affect the availability of intermediate host populations, as well as the feeding and reproductive behavior of the host., Competing Interests: Declaration of competing interest The authors report that no competing interests exist., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The coastal waters of Vietnam are home to a wide diversity of fishes, but the parasite diversity of these potential hosts is much less well characterized. To begin addressing this knowledge gap, we carried out surveys of myxozoan parasites in fishes collected from Nha Trang Bay in Vietnam's East Sea in 2018-2019. Mugilid fishes were collected in March-April 2018, January-February 2019, and November-December 2019, and examined for myxozoans. Myxospores consistent with those of the genus Ellipsomyxa were found in the gall bladder of four mullet species, and we thoroughly characterized those from Planiliza melinoptera. Myxospores were elliptoid and devoid of striation, with a distinct sinuous suture line. Polar capsules were pyriform and oriented toward the poles of the spore. Morphological features were compared to nominal species and this species from Vietnam was distinct. Phylogenetic analysis based on partial small subunit rDNA sequence revealed that broadly, Ellipsomyxa species split into three phylogenetic lineages, and although in some branches there are groupings by host family, habitat or locality, there are no clear phylogenetic patterns. The new species we encountered in P. melinoptera had a close sister relationship with Ellipsomyxa adlardi, with both species part of a larger subclade within the Ellipsomyxa lineage. Despite this phylogenetic similarity, these species were morphologically distinct, and partial large subunit DNA sequences were only 93% similar to each other. A combination of the morphological characteristics and molecular data suggest that this is an undescribed species and we propose the name Ellipsomyxa gordeyi n. sp., Competing Interests: Declaration of competing interest The authors declare they have no conflict of interest or competing interests. ORCID. Yurakhno, VM: 0000–0002–0571-6716. Ha,VT:0000–0001-7740-954×. Whipps, CM: 0000–0001–6139-0426., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The ectoparasite Amyloodinium ocellatum is a dinoflagellate that causes severe morbidity and mortality in both brackish and marine warmwater aquaculture fishes worldwide. A. ocellatum has a triphasic life cycle based on a free-living flagellate (the dinospore), a parasitic stage (the trophont) and a resting and reproductive cyst (the tomont). Current chemical treatments have shown some efficacy in eliminating dinospores but fail to inactivate the tomonts. Here we evaluated the efficacy of alternative treatments in vitro through sporulation tests and the quantification of dinospore production and motility. Hydrogen peroxide and peracetic acid efficiently decreased dinospore production at low concentrations, but total inactivation of tomonts was only achieved with higher dosages. Tomont inactivation was also observed with disinfectants such as sodium hypochlorite and Virkon S. This work provides insights into effective and environmentally friendly alternatives for the elimination of resistant forms of the marine parasite A. ocellatum.

In this study, we compared the efficacy of geometric morphometric techniques, including outlines and landmark-based approaches, to support the differentiation of Trichodina bellottii from three co-occurring killifish species. Both methods were able to differentiate trichodinids from different host species. However, discriminat analyses and MANOVA results based on landmarks had greater accuracy possibly because these analyses only provide information on certain points defined by the researcher, while the analyses based on outlines take into account points with less taxonomic information., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The tapeworms belonging to the order Caryophyllidea (Platyhelminthes, Eucestoda) represent a widespread group of intestinal parasites found in cypriniform and siluriform fishes. This group comprises four families (Balanotaeniidae, Capingentidae, Caryophyllaeidae, Lytocestidae), 42 genera and approximately 130 described species. Additionally, over a hundred new taxa have been reported from India. While many of these taxa are endemic and have unique evolutionary importance, a considerable number of putative new taxa were also invalidated because the quality and reliability of the published data did not meet the requirements. Various researchers have synonymised 28 species into a single representative, Lytocestus indicus (Moghe, 1925) Woodland, 1926. Consequently, L. indicus was chosen as a model organism to investigate whether there is taxonomic inflation or hidden diversity. Newly collected specimens of L. indicus were subjected to various fixatives for morphological assessment, and hologenophores of the same were obtained to determine whether true variations exist in their genotype or if they are merely fixation-induced variations. Despite morphological variations associated with fixation, molecular data indicated that they were indeed the same specimens. The taxonomic status of 43 new taxa was critically evaluated, with most of them tentatively synonymised with L. indicus. Others were also found to be conspecific with L. indicus but were classified as unavailable names based on their first description in unpublished dissertations., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Aggregation is a fundamental feature of parasite distribution in the host population, but the biological implications of the aggregation indices used to describe the relationships between the populations of parasites and hosts are not evident. It is speculated that the form of distribution in each case is predicated on the host's varying resistance to the infection, which is hard to control, making it difficult to adequately interpret the index values. This paper examines several cases from trout farms in Russian Karelia to explore the monogenean Gyrodactylus spp. infection in rainbow trout of varying ages. The genetic homogeneity of cage-reared fish and the direct life cycle of the helminths make the relationship between the species more lucid than in natural host-parasite systems. The results give no ground to speak of any specific patterns: as well as in the natural systems, the infection rates in trout vary widely, i.e., the helminth distribution has not become more uniform; the observed distributions in all cases are adequately approximated by the negative binomial model; the positive abundance-occupancy relationships (AORs) and abundance-variance relationships (AVRs) common for parasitic systems apply to the basic infection parameters. The form of the negative binomial distribution is shaped by two parameters-k and θ, the former being a metric of the infection variability, which depends on the host's individual resistance, and the latter representing the parasites' reproduction and establishment success rates. A rise in the parameter k indicates increased aggregation and a higher parameter θ points to a more uniform frequency distribution. These parameters can be used as a representative tool for monitoring the parasite communities in salmonid fishes, including in aquaculture., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

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. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision.

This study examined the metrics of the macroparasite community in fishes from the Jaguaribe River basin, state of Ceará, before and after receiving water from the São Francisco River in Northeastern Brazil. This research assessed the association of environmental factors (water parameters) and the traits of 30 fish species on the parasite richness and abundance across space (river course) and time (seasons, pre- and post-transposition periods). Generalized linear models reveal associations between parasite metrics and host traits, water parameters, and river sub-basin. Host size and body condition positively correlated with parasite richness and abundance, while reproductive phase was negatively related. Water quality impacted ecto- and endoparasites differently, with seasonal and sub-basins variations and differences among sub-basins. The general models also indicate that the period is a significant variable, where parasite richness decreases while abundance increases in the post-transposition period. This study underscores the importance of considering diverse environmental and host variables for understanding parasite dynamics in river ecosystems. These findings could lead to valuable insights for ecosystem management and conservation, elucidating the potential consequences of environmental alterations on parasite-host interactions and ecosystem health., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Three fish blood flukes (Aporocotylidae Odhner, 1912) infect mullets (Mugiliformes: Mugilidae): Cardicola mugilis Yamaguti, 1970 and Plethorchis acanthus Martin, 1975 infect striped mullet, Mugil cephalus Linnaeus, 1758 in the Central Pacific Ocean (Hawaiian Islands) and Brisbane River (Australia), respectively; Cardicola brasiliensis Knoff & Amato, 1992 infects Lebranche mullet, Mugil liza Valenciennes, 1836 from the Southwestern Atlantic Ocean (Brazil). White mullets were cast-netted from the mouth of Deer River, a coastal saltmarsh of Mobile Bay, in the north-central Gulf of Mexico and examined for blood fluke infections. Specimens of Mugilitrema labowskiae Warren & Bullard n. gen., n. sp. were found infecting the endocardial surface and inter-trabecular spaces of the atrium, ventricle, and bulbous arteriosus. The new genus and species differ from all other aporocotylids by having the combination of two post-caecal testes, a uterus with straight ascending and descending portions, and a common genital pore. The 28S analysis recovered the new species and P. acanthus as sister taxa and Aporocotylidae as monophyletic. Carditis associated with intense infections comprised endocardial hyperplasia, resulting in a thickened cardiac endothelium. Probable dead or deteriorating eggs in the myocardium were encapsulated by granulomas composed of epithelioid histiocytes. Live eggs infected the afferent artery of gill filaments and were associated with varied hyperplasia of the overlying epithelium and haemorrhaging from the afferent artery in high-intensity infections. The new species is the first aporocotylid infecting a mullet from the northwestern Atlantic Ocean and only the second description of demonstrable endocarditis attributed to an adult fish blood fluke infection.

In the aquaculture industry, biocides are routinely used to treat parasitosis in fish, and researchers are continually developing sustainable alternatives that can replace these harsh chemicals. In this context, the objective of this study was to evaluate the effectiveness of a new natural compound, BiokosTM, for the treatment against Epistylis sp. in Carassius auratus fish. The infestation was identified by the presence of whitish plaques on the integument of five animals, and the diagnosis was confirmed through skin scrapings. BiokosTM is a lipopeptide derived from the bacteria Pseudomonas that can destroy the functionality of the cell membrane of ciliated protozoa. The action of BiokosTM does not harm animals and the environment because the compound degrades into amino acids and fatty acids within days. A 0.15 m3 (150 L) aquarium was treated with an Ich-AwayTM water conditioner manufactured by the Danish company Sundew ApS, which has BiokosTM as the active ingredient. Six tablets were added to the water daily for two days, and new skin scrapings were performed. The fish were clinically well and no longer possessed lesions or parasites. The results obtained indicate that BiokosTM can be an innovative and more sustainable alternative for controlling epistyliasis in ornamental fish.

The spotted seatrout, Cynoscion nebulosus, is a popular game fish in the southeastern USA. It is estimated that nearly 90% of the adult population in South Carolina estuaries are infected in their skeletal muscle by the myxosporean, Kudoa inornata. However, little is known about this parasite's biology, including the distribution and densities of myxospores within tissues of infected fish, which we expect affect the physiology of their hosts. In order to correlate densities with physiological parameters in future studies, we quantified the myxospores density in muscle and characterized the variation among individual fish. Naïve juvenile seatrout was experimentally infected via presumed K. inornata actinospores exposure to raw seawater. A plug of muscle was extracted from two bilaterally symmetrical regions in the epaxial fillet from fresh and frozen carcasses. Variation in density data was calculated both within and among individuals. Within individuals, density counts were compared between left- and right-side biopsies. There was no significant difference between fresh and frozen plugs, and variation among individuals accounted for the greatest proportion of variation at 68.8%, while variation within individuals was substantial at 25.6%. Simulation and correlation tests confirmed that bilaterally symmetrical replicates varied significantly within individuals. When sampled from areas surrounding the initial biopsies, myxospore density estimates were more similar than between sides. Our findings have important implications for sampling design, particularly for studies investigating physiological parameters at the cellular or molecular level in association with parasite infection., (© 2024. The Author(s).)

Myxozoans are microscopical parasites widely distributed in fish, with over 2,600 described species, but their actual diversity is still underestimated. Among salmonids, more than 70 myxozoan species have been identified. This study focuses on species of Chloromyxum Mingazzini, 1890 that infect salmonid kidneys, particularly C. majori Yasutake et Wood, 1957 and C. schurovi Shulman et Ieshko, 2003. Despite their similar spore morphology, they exhibit distinct host preferences, tissue affinities and geographical distributions. Chloromyxum schurovi predominantly infects the renal tubules of Salmo salar Linnaues and S. trutta Linnaeus in Europe, while C. majori targets the glomeruli of Oncorhynchus mykiss (Walbaum) and O. tshawytscha (Walbaum) in North America. The sequence data for C. majori and C. schurovi have been either missing or questionable. In our study, we examined the kidneys of two salmonid species for chloromyxid infections, using both morphological and molecular data to characterise Chloromyxum species in salmonids. The sequence of C. schurovi obtained in our study did not match the previously published parasite data. Instead, it clustered as an independent lineage sister to the Paramyxidium Freeman et Kristmundsson, 2018 clade gathering the species from various fish organs, including the urinary tract. Our findings clarified the taxonomic origin of the previous C. schurovi sequence as Myxidium giardi Cépède, 1906, highlighting the risks associated with the presence of myxozoan blood stages in the bloodstream of their fish host and the challenges of non-specific PCR amplification. We redescribe C. schurovi, thus contributing to a better understanding of the diversity and phylogeny of kidney-infecting species of Chloromyxum.

The practice of hybridization is carried out globally in fish farms. Here, we present the first record of the parasitic fauna of hybrids among genus Colossoma and Piaractus in natural environments. We identified a total of 48 hybrids, nine F1 hybrids (nuclear DNA from both species present in the cross) and 38 advanced hybrids (nuclear DNA from one species), both from crosses between Piaractus brachypomus and Piaractus mesopotamicus, and one F1 "tambacu" corresponding to cross between Colossoma macropomum and Piaractus mesopotamicus. This is the first record of Anacanthorus penilabiatus, Anacanthorus toledoensis, Mymarothecium viatorum, Mymarothecium ianwhittington, Haementeria sp., Dadaytrema oxycephala, Rondonia rondoni, and Echinorhynchus gomesi parasitizing hybrids collected in a natural environment. With this, we expand knowledge about the diversity of fish and parasites in the upper Paraná River and warn about the risk that fish escapes can cause in the basin., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Nematodes collected from the intestine of sompat grunt Pomadasys jubelini Cuvier, 1830 from Hann Bay in Dakar, Senegal represent a new species described herein as Dichelyne (Neocucullanellus) dakarensis n. sp., and investigated with the use of light and scanning electron microscopy. The new species differs from its congeners based on several characteristics, especially because the subgenus Neocucullanellus is the only 1 that has 2 ceca. In addition, the new species diagnosis is based on the number and arrangement of the caudal papillae as well as the size of the veil of spicules. Morphological data were supported by molecular analysis. Results obtained using SSU rDNA and COI distinguished the present specimens from other cucullanids. Molecular data indicated the close relatedness between the new species and Dichelyne cotylophora Ward and Magath, 1917., (© 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: The influence of two key factors, host length and infection site, on the host-parasite interaction in Ompok bimaculatus (Butter catfish) from Mukutmanipur Dam Lake, were investigated., Methods: Present study involved 192 specimens of Ompok bimaculatus with varying body lengths, subjected to diverse statistical analyses. One-way analysis of variance (ANOVA) was performed for the parasite numbers for three groups (cestode, nematode and trematode). Subsequently, we conducted one-way permutational multivariate analysis of variance (PERMANOVA) followed by pairwise test to assess parasite numbers across three body sites (intestine, mesentery, and bodycavity), employing the Bray-Curtis index. Additionally, Principal Coordinate Analysis (PCoA) for the same dataset was performed using the same index. Linear regression analysis was performed for the fish length-cestode number, fish length-nematode number, fish length-trematode number and fish length-total parasite number., Results: One-way ANOVA revealed no significant differences in parasite numbers among the three endo-helminth groups (cestode, nematode, and trematode). The results of PERMANOVA revealed significant differences in parasite numbers across the three body sites of the host fishes (groups) (F = 9.41, p = 0.0001). Pairwise tests further demonstrated significant differences between the intestine-mesentery, intestine-body-cavity, and mesentery-body-cavity. Additionally, Principal Coordinate Analysis (PCoA) unveiled a significant relationship between infection site and parasite number. However, linear regression analysis examining the relationship between fish length and parasite abundance indicated no significant associations., Conclusions: Through a detailed exploration of the statistical analyses, we provide insights into the host-parasite interaction, elucidating both established knowledge and novel findings in fish parasitology., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Purpose: This paper aims to describe Plenivitellinum kifi n. gen., n. sp. (Digenea: Azygiidae) infecting the gastrointestinal tract of the African tigerfish, Hydrocynus vittatus Castelnau, 1861 (Characiformes: Alestidae) in the Kavango River, Namibia. We revise the diagnosis of Azygiidae Lühe, 1909 to accommodate this new species., Methods: The worm was heat-killed, fixed in 10% neutral buffered formalin, stained in Van Cleave's and Ehrlich's hematoxylins, cleared in clove oil, and mounted on glass slide using Canada balsam., Results: The new azygiid resembles species of Otodistomum Stafford, 1904 by having an elongate body, a ventral sucker that is wider than the oral sucker and that is in the anterior half of the body, a pre-testicular ovary, a uterus that primarily occupies the inter-caecal space between the ovary and the ventral sucker, and a vitellarium that is restricted to the hindbody and that is confluent posteriorly in the post-testicular region. The new genus differs from all species of Azygiidae by having the combination of a ventral sucker that is wider than the oral sucker (vs. narrower), an elongate prostatic sac that extends posteriad to near the posterior margin of the ventral sucker (vs. an ovoid prostatic sac that is wholly anterior to or slightly overlaps the anterior margin of the ventral sucker), a vitellarium that nearly fills the post-testicular space and that extends posteriad beyond the caecal tips (vs. a vitellarium that is separate posteriorly or that is restricted to the anterior half of the post-testicular space and does not extend posteriad beyond the caecal tips), and an I-shaped excretory bladder (vs. Y-shaped)., Conclusion: This study documents the first record of an azygiid from Africa and the first record of an azygiid infecting a characiform fish., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Objective: We sought to evaluate accurate and reproducible detection of Myxobolus cerebralis (Mc), the causative agent of whirling disease, by using nested polymerase chain reaction (nPCR) and three previously established real-time quantitative PCR (qPCR) assays: K18S (Kelley 18S), C18S (Cavender 18S), and Hsp70 (heat shock protein 70). We used a "fit for purpose" approach combined with intra- and interlaboratory testing to identify a molecular testing method that would be equivalent to the currently accepted nPCR procedure for Mc., Methods: Assay performance was compared using a combination of intra- and interlaboratory testing that used synthetic gBlocks along with naturally and experimentally infected fish tissue. North American isolates representing geographically distinct locations were also tested using all three assays., Result: The K18S and C18S assays exhibited high assay sensitivity, intra- and interlaboratory repeatability of sample replicates, and reproducible identification of all test samples across multiple laboratories. In contrast, the Hsp70 assay failed to detect several positive samples at low DNA concentrations during intra- and interlaboratory testing. The K18S assay was the only procedure that demonstrated perfect detection accuracy when testing geographically distinct Mc isolates. Results demonstrated the K18S assay is robust under variable test conditions, is more accurate than the C18S and Hsp70 assays, and provides detection capabilities equivalent to those of the currently accepted nPCR confirmation assay "gold standard" that is described in the American Fisheries Society-Fish Health Section (AFS-FHS) Blue Book., Conclusion: The "fit for purpose" approach and preliminary completion of the World Organization for Animal Health validation pathway demonstrate that the K18S assay provides an alternate method for Mc testing. This work provides the foundation for acceptance of the K18S assay into the AFS-FHS Blue Book as a standardized test procedure for Mc., (© 2024 American Fisheries Society.)

Purpose: In this study, 143 lutjanid fishes representing four different species from the Northeast coast off Brazil were analyzed for parasites. The aim of the present study is to provide a detailed redescription of R. (I.) vicentei, collected from lutjanid fishes in Brazil, including the first observation of the species using scanning electron microscopy (SEM)., Methods: Nematodes found clarified in a crescent glycerin series, were photographed and measured (in mm), and some specimens destined for SEM. The Illustrations were made using an optical microscope with a drawing tube., Results: Nematodes found were identified as Raphidascaris (Ichthyascaris) vicentei, infecting 6.29% of the examined fish. Detailed morphological analysis revealed the following characteristics observed for the first time in this species: labial papillae, narrow lateral alae and the detailed structure of male spicules. These contributions help filling the gaps in the literature and expand the knowledge of this parasite morphology., Conclusions: The presence of R. (I.) vicentei in four lutjanid species may indicates low host specificity, highlighting its adaptability to different hosts. Furthermore, new host records are given. This research provides the most comprehensive morphological description of R. (I.) vicentei to date, generating crucial insights for a better understanding of the parasitic biodiversity off the Brazilian Northeastern coast of Brazil, as well as establishing foundation for future investigations on the ecology and impacts of these parasites in fish populations from this region., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Artificial light at night (ALAN) negatively impacts organisms in many ways, from their feeding behaviors to their response and ability to deal with disease. Our knowledge of ALAN is focused on hosts, but we must also consider their parasites, which constitute half of all described animal species. Here, we assessed the impact of light exposure on a model host-parasite system (Poecilia reticulata and the ectoparasitic monogenean Gyrodactylus turnbulli). First, parasite-free fish were exposed to 12:12 h light:dark (control) or 24:0 h light:dark (ALAN) for 21 days followed by experimental infection. Second, naturally acquired G. turnbulli infections were monitored for 28 days during exposure of their hosts to a specified light regime (6:18 h, 12:12 h, or 24:0 h light:dark). Experimentally infected fish exposed to constant light had, on average, a greater maximum parasite burden than controls, but no other measured parasite metrics were impacted. Host feeding behavior was also significantly affected: fish under ALAN fed faster and took more bites than controls, whilst fish exposed to reduced light fed slower. Thus, ALAN can impact parasite burdens, even in the short term, and altering light conditions will impact fish feeding behavior. Such responses could initiate disease outbreaks or perturb food-webs with wider ecological impacts., (© 2024 The Author(s). Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

Purpose: Molecular phylogenetics has been improving the acanthocephalan systematics, yet numerous taxa remain unexplored. The palaeacanthocephalan Metarhadinorhynchus Yamaguti, 1959 and its type species M. lateolabracis Yamaguti, 1959 are such to-be-explored taxa. We aim to refine (i) the systematic placement, (ii) the morphological circumscription, and (iii) the taxonomic components of the genus. We also aim to examine the taxonomic status of the species that have been assigned to the genus., Methods: Morphological observations on newly collected specimens as well as the type material of Metarhadinorhynchus lateolabracis were conducted. Also, molecular phylogenetic analyses with maximum-likelihood method and Bayesian inference were performed based on freshly collected specimens. Nominal species that have at least once been assigned in Metarhadinorhynchus, as well as a related form, Gorgorhynchus lateolabri Yin and Wu, 1984, are taxonomically re-evaluated based on literature information., Results: Our re-examination of the type material of M. lateolabracis revealed that the number of cement glands is six, instead of eight as described and illustrated in the original description. In the resulting phylogenetic tree, M. lateolabracis was nested in Isthmosacanthidae. Gorgorhynchoides Cable and Linderoth, 1963 was found to be a junior synonym of Metarhadinorhynchus. Taxonomic re-evaluations of six nominal species that have once belonged in Metarhadinorhynchus led to modifications of generic diagnoses for Indorhynchus Golvan, 1969 and Neotegorhynchus Lisitsyna, Xi, Orosová, Barčák, and Oros, 2022., Conclusions: Metarhadinorhynchus has been assigned to Leptorhynchoididae (Echinorhynchida), but our study now locates it in Isthmosacanthidae (Polymorphida). We propose 13 new combinations of specific names in Metarhadinorhynchus and three in Indorhynchus. Metarhadinorhynchus lateolabri (Yin and Wu, 1984) comb. nov. may be synonymous with M. orientalis (Wang, 1966) comb. nov., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

The increasing significance of the aquaculture sector and commercially valuable species underscores the need to develop alternatives for controlling diseases such as Ichthyophthirius multifiliis-induced ichthyophthiriasis. This ciliated protozoan parasite threatens nearly all freshwater fish species, causing substantial losses in the fishery industry. Despite this, effective large-scale treatments are lacking, emphasizing the necessity of adopting preventive strategies. While the pathogenesis of ichthyophthiriasis and its immune stimulation allows for vaccination strategies, precise adjustments are crucial to ensure the production of an effective vaccine compound. Therefore, this study aimed to evaluate the impact of immunizing Astyanax lacustris with a genetic vaccine containing IAG52A from I. multifiliis and the molecular adjuvant IL-8 from A. lacustris. Transcript analysis in immunized A. lacustris indicated mRNA production in fish muscles, demonstrating an expression of this mRNA. Fish were divided into five groups, receiving different vaccine formulations, and all groups received a booster dose 14 days after the initial immunization. Samples from vaccinated fish showed increased IL-1β mRNA expression in the spleen within 6 h post the second dose and after 14 days. In the head kidney, IL-1β mRNA expression showed no significant difference at 6 and 24 h but an increase was noted in fish injected with IAG and IAG + IL-8 after 14 days. IL-8 mRNA expression in the spleen and kidney did not significantly differ from the control group. Histological analysis revealed no variation in leukocyte concentration at 6 and 24 h post-vaccination; however, after 14 days, the groups injected with IAG and IAG + IL-8 exhibited a higher leukocyte density at the application sites than the control. The obtained data suggest that the used vaccine is transcribed, indicating its potential to stimulate innate immune response parameters through mRNA cytokine expression and leukocyte migration., (© 2024 John Wiley & Sons Ltd.)

Elasmobranch populations are in steep decline mainly due to overfishing bycatch, but parasites may accelerate the collapse of vulnerable and/or highly parasitized species. We therefore studied metazoan parasites of Rajidae from the northeast Atlantic: vulnerable Leucoraja fullonica, near-threatened Raja brachyura, Raja clavata, Raja microocellata and Raja undulata, and least-concerned Raja montagui and Leucoraja naevus. Overall prevalence varied from 19% for R. montagui to 100% for L. fullonica. Parasite communities differed between skate species, and prevalence and abundance were higher for L. fullonica, R. microocellata, and R. undulata. We recorded 11 parasite taxa in the study: three nematodes, six cestodes, one monogenean, and one myxosporean. Whatever the skate species, the parasite component community comprised at least two nematode taxa among Phocanema spp., Proleptus sp. and Anisakis simplex. DNA-sequencing revealed that Phocanema azarasi and Phocanema krabbei both occurred in R. microocellata and R. undulata. Phocanema spp. was first recorded in L. fullonica, L. naevus, R. microocellata, R. montagui, and R. undulata, as Proleptus sp. in L. fullonica, and A. simplex in L. fullonica and R. clavata, Rockacestus sp. and Nybelinia sp. in R. undulata, and gill-myxosporeans on L. fullonica, L. naevus, R. microocellata, and R. undulata. The occurrence of 16 new host-parasite associations suggests potential environmental changes. Information provided by trophically transmitted helminths confirmed an opportunistic skate diet based on crustaceans and fish. We discuss results in terms of host fitness loss, bioindicator role of parasites, and anisakiasis risk. We recommend incorporating parasitology in research to improve elasmobranch conservation., (© 2024 The Author(s). Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

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.)