Systematic assessment of nymphs of Diesingiinae (Pentastomida: Sebekidae) parasitizing Palloceros harpagos (Cyprinodontiformes: Poeciliidae) from Parque Nacional Iguazú, Argentina: filling gaps in an incomplete phylogenetic framework.

During a search for parasites in fishes from Iguazu River, Argentina, a nymph of pentastomid was found encysted on mesenteries of Phalloceros harpagos. The 28S rDNA and COI mt-DNA were used to compare with the sequences deposited in the GenBank. Pentastomid nymphs belong to the subfamily Diesingiinae (Sebekidae) for having chloride cell pores distributed in a single row per annulus; also, the hooks and rows of spines of our material differ to other genera. Present specimens are most likely Diesingia sp., having 63-74 annuli, a U shaped oral cadre with fibers closing anteriorly and a peg like extension of the oral cadre. The 28S rDNA analysis places our samples into a sister group of Alofia sp., but the COI mt-DNA situate them on the base of the clade. In conclusion, our pentastomid positively belongs to Diesingia sp., however, indisputable assignation requires a reliable description of the nymph, or the availability of sequences linking nymphs and adults, which even could provide evidence of a new hitherto undescribed genus. Aditionally, the systematic position of Sebekia oxycephala previously described by P. harpagos is discussed on the basis of our results, allowing us to suggest a re-assignation of such specimens to the genus Diesingia.

Characterisation of myxozoan fauna of western mosquitofish, Gambusia affinis (Baird and Gerard) (Cyprinodontiformes: Poeciliidae), inhabiting experimental catfish ponds in Mississippi, USA.

Characterising myxozoan taxa parasitising fish hosts in catfish aquaculture ponds is crucial to understanding myxozoan community dynamics in these diverse and complex ecological systems. This work investigated the myxozoan fauna of the western mosquitofish, Gambusia affinis, a common, incidental species found in catfish aquaculture ponds in the southeastern United States. 598 fish were sampled in May of 2018 and 2019 from the pond facility of the Thad Cochran National Warmwater Aquaculture Center in Stoneville, Mississippi, USA. Fish were examined microscopically using wet mount preparations of fresh tissue and histology for myxozoans. 18S rRNA gene sequences were amplified from myxospores obtained at necropsy. Updated morphologic, histologic, and 18S rRNA gene sequence features are provided for Henneguya gambusi, Myxobolus pharyngeus, and Myxidium phyllium. Two potentially novel myxozoans were observed during this survey, an undocumented Myxobolus sp. associated with chondrolysis of bones throughout the body and a putative Myxobilatus sp. observed histologically in the renal tubules, ureters, and urinary bladder. However, inadequate samples were obtained for proper species descriptions. Lastly, the life cycle of M. pharyngeus, which is thought to utilize the oligochaete worm Dero digitata as their definitive host, was putatively confirmed by 18S rRNA sequence matching to actinospore stages from oligochaetes in catfish ponds in Mississippi. This work provides novel and expanded morphologic, histologic, molecular and biologic data of five myxozoan parasites of G. affinis, expanding our knowledge of myxozoan diversity in catfish aquaculture ponds.

Two new species of Gyrodactylus von Nordmann, 1832 parasitizing Cnesterodon decemmaculatus (Poeciliidae) from the southern limit of the family in the Neotropical region.

In this study, we followed an integrative taxonomy approach to describe two new species of Gyrodactylus von Nordmann, 1832, and to identify specimens of G. breviradix Vega, Razzolini, Arbetman, and Viozzi, 2019, all three collected from ten spotted live-bearer Cnesterodon decemmaculatus (Jenyns, 1842), an endemic and widespread poeciliid from the Pampean region, which is the southernmost occurring species of the Poeciliidae in the Americas. Gyrodactylids were first characterized morphologically and mophometrically, and when possible, sequences of the Internal Transcribed Spacers (ITS1-5.8S-ITS2) and the cytochrome oxidase II (COII) were used to delimit species. Gyrodactylus breviradix, Gyrodactylus marplatensis n. sp., and Gyrodactylus pampeanus n. sp. were found on the fins and body surface of C. decemmaculatus in La Tapera Creek, Mar del Plata, Buenos Aires province, Argentina. A phylogenetic analysis combining newly generated sequences of one of the new species, G. marplatensis n. sp., and of G. breviradix, along with those available in GenBank for a further 36 species of Gyrodactylus, revealed that G. marplatensis n. sp. is a sister taxon of Gyrodactylus decemmaculati Vega, Razzolini, Arbetman, and Viozzi, 2019. Genetic distances for the ITS and COII gene were estimated among Gyrodactylus spp. and further supported the validity of the new species. Overall, morphometric and molecular data coincided in delimiting the new taxa, thus demonstrating the value of integrative taxonomy for the erection of new species of Gyrodactylus and species identification.

Morphological and Molecular Evidence for a New Rhabdochonid Species (Nematoda: Rhabdochonidae) Parasitizing Profundulus oaxacae (Profundulidae) in the State of Oaxaca, Mexico.

The genus Rhabdochona Railliet, 1916 is one of the most speciose group of nematodes, parasites of freshwater fishes, with approximately 103 species described worldwide. Twenty-two species have been recorded in the Americas, 14 of them in Mexico. In this paper we describe a new species of Rhabdochona on the basis of light and scanning electron microscopy and molecular tools. Rhabdochona adentata n. sp. was recovered from the gallbladder of the freshwater Oaxaca killifish, Profundulus oaxacae (Meek, 1902) (Profundulidae) captured in the Río Grande, State of Oaxaca, Mexico. Rhabdochona adentata n. sp. differs markedly from its congeners by possessing an unusual prostom lacking anterior teeth, small simple deirids, and the location of the excretory pore at the level of the union of the muscular and glandular esophagus. Sequences of cytochrome c oxidase subunit I (COI) from mitochondrial deoxyribonucleic acid and the D2 + D3 domains of the large ribosomal subunit (28S) were obtained from 3 specimens and were analyzed using maximum likelihood and Bayesian inference analyses. Phylogenetic analyses using COI and 28S genes recovered 1 new lineage of Rhabdochona. The new species is described on the basis of a detailed morphological study. This parasite represents the first species of Rhabdochona without prostomal teeth and with a different site of infection, the gallbladder.

Parasitism in Gambusia affinis: Fitness Effects in an Incipient Matrotroph.

Gambusia affinis (western mosquitofish) serves as a host for a variety of larval and adult parasites. Gambusia affinis is also an incipient matrotroph, exhibiting adjustments in post-fertilization provisioning to some offspring within a brood using recently acquired resources. Nutrient transfer to embryos is expected to limit the loss of embryo mass during development resulting in larger offspring. Since larger offspring are more likely to survive, maternal contributions are expected to increase fitness. The presence of parasites, particularly intestinal helminths, potentially reduces body condition and resources available for developing offspring, thereby reducing host fitness. The effects of parasitism on the fitness of G. affinis were investigated in the present study. Fish were collected from 3 sites monthly from June 2015 through August 2016. All helminth parasites were collected during necropsy and identified. Brood size and embryo developmental stage were recorded for each female fish. Additionally, 10 ova/embryos of each developmental stage from each female fish collected from May through August 2016 were haphazardly selected and individually weighed. From 429 female mosquitofish, 5,072 helminths were collected. Brood size varied among collection sites and was positively influenced by maternal body condition, the number of daylight hours, water temperature, and the intensity of both plerocercoid and adult Schyzocotyle acheilognathi. However, brood size was negatively related to the intensity of Neoechinorhynchus cylindratus cystacanth and an increasing number of days between collection and dissection. Embryo weight increased with the presence of either Camallanidae or Contracaecum multipapulatum, embryo developmental stage, and relative host density. These results indicate that some parasitic helminth species negatively affect the fitness of G. affinis, while some positively affect fitness, and that effect can vary with intensity.

Variation in Helminth Parasite Component Communities of Gambusia affinis.

In north-central Texas streams, seasonal changes in ambient temperature and rainfall result in dynamic variation in microhabitat structure, affecting the distribution and abundance of hosts. Since the complex life cycles of parasites require the presence and interaction of multiple hosts, the seasonal variations in microhabitats could influence parasite component communities within these ecosystems. Gambusia affinis (western mosquitofish) serves as a host for a variety of larval and adult parasites. Factors that affect helminth component communities in populations of mosquitofish from the Paluxy River were investigated in this study. Gambusia affinis individuals were collected from 3 sites monthly from June 2015 through August 2016. All helminth parasites were collected during necropsy and subsequently identified. From 495 mosquitofish, 5,283 helminths were collected. Component community diversity varied among collection sites and collection dates and was positively influenced by river flow. These results indicate that helminth assemblages infecting mosquitofish in the Paluxy River vary through time and space, as well as in response to environmental variation (i.e., changes in water flow).

Molecular and Histopathological Data on Levisunguis subaequalis Curran, Overstreet, Collins & Benz, 2014 (Pentastomida: Eupentastomida: Porocephalida: Porocephaloidea: Sebekidae: Sebekinae) from Gambusia affinis in Alabama, USA.

Levisunguis subaequalis Curran, Overstreet, Collins & Benz, 2014 , was recently described from the lungs of the definitive hosts, softshell turtles, Apalone ferox (Schneider, 1783), and Apalone spinifera aspera (Agassiz, 1857) as well as the viscera of an intermediate host, the western mosquitofish, Gambusia affinis (Baird and Girard, 1853). However, the original account lacked molecular data. Furthermore, histological examination of infected host tissues in the original account of L. subaequalis did not reveal any pathological changes in the intermediate host. The present work provides a robust morphological description of the nymph and novel molecular data from the 18S and 28S ribosomal gene regions and the cytochrome c oxidase subunit 1 (COI) mitochondrial gene. Phylogenetic analyses using Bayesian inference and maximum likelihood analysis with concatenated sequence data from these 3 regions, as well as each region individually, placed the turtle pentastomid L. subaequalis as a sister clade to the crocodilian pentastomids of the genus Sebekia Sambon, 1922. While only concatenated phylogenetic analyses agreed with the currently accepted classification of the Eupentastomida and phylogenetic signal assessment indicated that the concatenated data set yielded the most phylogenetic signal, data from more taxa are still needed for robust phylogenetic inferences to be made. The intensity of infection ranged from 2 to 171 nymphs per fish, compared with the highest previously reported intensity of 6. These high-intensity infections with L. subaequalis were characterized by the nymphs occupying 5-50% of the coelomic cavity of G. affinis. However, despite this heavy parasite infection, fish exhibited minimal pathology. Observed pathology was characterized by compression or effacement of organs adjacent to the nymphs, particularly liver, swim bladder, and intestines, as well as the formation of granulomas around shed pentastomid cuticles. Nonetheless, the morphological and molecular data provided in the present work will bolster future efforts to identify this pentastomid in other hosts where pathology may be present in addition to aiding in the advancement of the field of molecular pentastomid systematics.

The role of freshwater fish in the life cycle of Dioctophyme renale in Southern Brazil.

Brazil stands out by the diverse records of Dioctopphyme renale in different hosts; however, there is little information about the life cycle of the nematode in the region. This study aims to report on third-stage larvae infections in fish in southern Brazil. In this context, 324 fish of different species belonging to Characiformes, Cyprinodontiformes and Siluriformes were collected in an urban area of Rio Grande do Sul State, where domestic and wild hosts were reported with the nematode. Of the total fish examined, 25(7.7%) were found to be parasitized by third-stage larvae of D. renale which were found encysted in the stomach serous membrane and in the celoma cavity of Hoplosternum littorale (Siluriformes) with a prevalence of 53.2% (25/47) and mean intensity of infection of 4.4 larvae/host (1 to 13 larvae). The occurrence of larvae in H. littorale indicates the presence of parasitosis in the region; however, the contribution of this fish species as a source of infection for dogs in urban areas must be considered with caution given the difficulties these dogs may face in the capture and predation of the fish to the point of effectively maintaining the urban cycle of D. renale. In addition, the low level of larvae registered in the total sample of fish examined indicates that these hosts are unlikely to play an important role in the transmission of D. renale to domestic animals in the region of the study.

Dendrorchis pampae sp. n. (Digenea: Gorgoderidae) from Cynopoecilus melanotaenia (Cyprinodontiformes: Cynolebiidae) a killifish from southern Brazil, with an emended diagnosis of Dendrorchis.

A new species of Dendrorchis is described and compared with others in the genus. The parasites were found in the swim bladder of the annual killifish Cynopoecilus melanotaenia. Hosts were collected from a seasonal wetland in southern Brazil. The main characteristics of D. pampae are: genital pore in the intestinal bifurcation region elongate and lobed vitellaria uterine loops limited to the acetabular region and to the rear end of the body; and wide intestinal caeca. An emended diagnosis of the genus Dendrorchis includes the characteristics of the new species. This is the first record of an adult digenean in an annual killifish from South America.

Two new species of Gyrodactylus von Nordmann, 1832 from Profundulus oaxacae (Pisces: Profundulidae) from Oaxaca, Mexico, studied by morphology and molecular analyses.

In the present study, two new species of Gyrodactylus are described from Profundulus oaxacae, a fish endemic to the Pacific slope of Oaxaca State, Mexico. Fishes were collected within their distribution range in 5 localities in the Atoyac-Verde River. Gyrodactylus montealbani n. sp. and G. zapoteco n. sp. were erected and characterized morphologically (sclerites of the attachment apparatus and the male copulatory organ) and molecularly (sequences of the Internal Transcribed Spacer region of rDNA). The haptoral sclerites of the new species are similar to those of Gyrodactylus iunuri and Gyrodactylus tepari, both recently described from the goodeid fish Goodea atripinnis, from the Mexican States of Jalisco and Querétaro, respectively; and to Gyrodactylus xtachuna described from the poeciliid Poeciliopsis gracilis in Veracruz State, Mexico - nonetheless, these species can all be discriminated based on their marginal hook morphology. Specimens of G. montealbani n. sp. and G. zapoteco n. sp. were sequenced, and were aligned with sequences of 25 other Gyrodactylus spp. Both Maximum likelihood and Bayesian inference analyses indicated that the two new species are members of independent, well-supported lineages - these are the first Gyrodactylus species described from Profundulus oaxacae.

Immune-Related Transcriptional Responses to Parasitic Infection in a Naturally Inbred Fish: Roles of Genotype and Individual Variation.

Parasites are strong drivers of evolutionary change and the genetic variation of both host and parasite populations can co-evolve as a function of parasite virulence and host resistance. The role of transcriptome variation in specific interactions between host and parasite genotypes has been less studied and can be confounded by differences in genetic variation. We employed two naturally inbred lines of a self-fertilizing fish to estimate the role of host genotype in the transcriptome response to parasite infection using RNA-seq. In addition, we targeted several differentially expressed immune-related genes to further investigate the relative role of individual variation in the immune response using RT-qPCR, taking advantage of the genomic uniformity of the self-fertilizing lines. We found significant differences in gene expression between lines in response to infection both in the transcriptome and in individual gene RT-qPCR analyses. Individual RT-qPCR analyses of gene expression identified significant variance differences between lines for six genes but only for three genes between infected and control fish. Our results indicate that although the genetic background plays an important role in the transcriptome response to parasites, it cannot fully explain individual differences within genetically homogeneous lines, which can be important for determining the response to parasites.

Three new species of Gyrodactylus von Nordmann, 1832 described from Goodea atripinnis (Pisces: Goodeidae), an endemic freshwater fish from the central highlands of Mexico.

Goodea atripinnis Jordan, 1880 has a broad range of habitats and is the most widespread species of the endemic goodeid fishes, which inhabit the central highlands of Mexico. This species is known to be host to a high diversity of helminth parasites from which only three belong to the genus Gyrodactylus von Nordmann, 1832: G. lamothei Mendoza-Palmero, Sereno-Uribe et Salgado-Maldonado, 2009, G. mexicanus Mendoza-Palmero, Sereno-Uribe et Salgado-Maldonado, 2009, and G. tomahuac Rubio-Godoy, Razo-Mendivil, García-Vásquez, Freeman, Shinn et Paladini, 2016. Here, we describe three new species of Gyrodactylus collected from G. atripinnis, which were characterised morphologically (sclerites of the attachment apparatus) and molecularly (sequences of the internal transcribed spacer region of the rDNA): Gyrodactylus iunuri n. sp., Gyrodactylus katamba n. sp. and Gyrodactylus tepari n. sp. These new species were collected in three different states in the Mexican Highlands: Guanajuato, Jalisco and Querétaro. Both morphological and molecular data support the hypothesis that two distinct groups of gyrodactylids infect goodeid fishes: G. iunuri n. sp., G. tepari n. sp. and G. tomahuac possess robust hamuli and are closely related phylogenetically; while G. katamba n. sp. resembles G. lamothei in having slender hamuli with accessory sclerites adjacent to the hamuli root, and apparently shares a common ancestor with gyrodactylids infecting poeciliid fishes. New locality records of G. tomahuac are presented. The addition of the three new species of Gyrodactylus as parasites of G. atripinnis makes monogeneans the second most abundant parasite group known to infect this host.

First Freshwater Bothriocephalidean (Cestoda) from Tropical South America, Closely Related to African Taxa.

Regobothrium microhamulinum n. gen. and n. sp. (Bothriocephalidea: Bothriocephalidae) is proposed to accommodate a new cestode from flatfish Catathyridium jenynsii (Chabanaud, 1922) (Pleuronectiformes: Acharidae; type host) and another 3 freshwater fishes of the orders Characiformes, Cyprinodontiformes, and Siluriformes in the Neotropical Region. The new genus is placed in the Bothriocephalidae because it possesses medioventral uterine and mediodorsal genital pores and a follicular vitellarium. Regobothrium n. gen. is characterized by possessing a tiny, slightly subovate scolex narrower than the strobila, with an apical disc armed with 2 semicircles of 15-17 tiny hooks in each and an acraspedote strobila. Regobothrium n. gen. differs from all bothriocephalid cestodes that have a scolex armed with hooks by their small size (maximum length less than 20 µm) and a triangular shape with the basal part (handle or basal plate) shorter than the distal coniform part (blade). In the other hooked bothriocephalids, hooks have a longer handle than a blade. Regobothrium microhamulinum n. gen. and n. sp. is the third bothriocephalidean cestode described from freshwater teleosts in South America but the first out of Patagonia. Molecular phylogenetics consider Regobothrium as a member of a lineage consisting of (up to now exclusively) freshwater bothriocephalids from the Ethiopian biogeographic region, thus indicating Gondwanan relationship.

Short communication: first report of nematodes parasitizing the four-eyed-fish, Anableps anableps (Pisces, Cyprinodontiformes).

The genus Anableps is composed of species Anableps anableps, Anableps dowi, and Anableps microlepis. These fishes are tropical and usually live on the surface of brackish water, being popularly known as four-eyed-fishes due to the presence of prominent eyes and a pupil split horizontally. A. anableps and A. microlepis are considered as sister species that live in sympatry in South America. A. dowi, however, is restricted to the Pacific Ocean (Central America) and is considered the most primitive species of this genus. The aims of this study were to investigate the presence of endoparasites in A. anableps from the Parnaíba's Delta and characterize them morphologically. During the necropsy, larvae of Contracaecum sp. in the third larval stage (L3) were collected from the pancreas of A. anableps, but no endoparasites were observed in other organs. The worms had a cuticular tooth and excretory pore located at the anterior end, a thread like body, whitish color, and without distinction of sex. The length of the ventricular appendix of the larvae was much greater than in other studies. This is the first report of endoparasitism in A. anableps and the first report of nematodes in four-eyed-fishes.

Triple trouble? Invasive poeciliid fishes carry the introduced tilapia pathogen Gyrodactylus cichlidarum in the Mexican highlands.

As part of ongoing surveys of the gyrodactylid parasite fauna of freshwater fishes in Mexico, we recorded the infection of three species of poeciliids (Poecilia mexicana, Poeciliopsis gracilis, and Pseudoxiphophorus bimaculatus [syn.=Heterandria bimaculata]) with Gyrodactylus cichlidarum, a monogenean parasite of cichlid fishes, which has been co-introduced globally with its translocated, African "tilapia" hosts. This tilapia pathogen was found on poeciliid fishes both within their native distribution range in the Gulf of Mexico slope, as well as on invasive species artificially introduced to the Mexican highlands, to rivers draining into the Pacific Ocean. Identity of G. cichlidarum was confirmed by morphological and molecular analyses. Prevalence and abundance of infection were low, but this is the first record of G. cichlidarum infecting poeciliids (Cyprinodontiformes), which are distantly related to this parasite's primary cichlid fish hosts (Perciformes). This study provides evidence that G. cichlidarum, a recognized pathogen which has been co-introduced globally with its cichlid fish hosts for aquacultural purposes, is able to infect non-related poeciliid fishes inhabiting water bodies adjacent to tilapia farms, thereby potentially increasing its ability to disperse between farms and different river basins. It is of particular concern that G. cichlidarum was found on poeciliids, as these invasive fishes have been introduced worldwide and could act as carriers for this parasite known to induce significant mortality of farmed tilapias - globally, the second most important freshwater aquaculture fish group, after the carps.

Molecular, Morphological, and Ecological Data of Saccocoelioides Szidat, 1954 (Digenea: Haploporidae) from Middle America Supported the Reallocation from Culuwiya cichlidorum to Saccocoelioides.

This study investigates the systematic position of some species of the genus Saccocoelioides Szidat, 1954, and the species Culuwiya cichlidorum Aguirre-Macedo and Scholz, 2005 , from North and Middle America using new morphological data and partial sequences of 2 nuclear genes, the large subunit and the internal transcribed spacer 2 from ribosomal DNA. In total 74 specimens representing 4 species of Saccocoelioides (41 of Saccocoelioides sogandaresi, 3 of Saccocoelioides chauhani, 6 of Saccocoelioides lamothei, and 12 of Saccocoelioides olmecae) plus 12 specimens of Culuwiya cichlidorum were analyzed. The phylogenetic analyses inferred with maximum likelihood method and Bayesian inference showed that the 4 species of Saccocoelioides formed a clade divided into 4 subclades representing each species. In addition, 7 specimens sequenced from the type host and locality of Culuwiya cichlidorum were nested in 2 clades: the first clade with specimens of C. cichlidorum from Costa Rica, and the second clade with specimens of S. sogandaresi from Mexico, Honduras, Nicaragua, and Costa Rica. Our analyses suggest that C. cichlidorum should be reallocated into Saccocoelioides, as was originally designated Saccocoelioides cichlidorum n. comb., is restricted to Nicaragua and Costa Rica and associated with cichlid fishes. In contrast, the specimens identified previously as Culuwiya cichlidorum from the coast of Gulf of Mexico by Aguirre-Macedo and Scholz belong to S. sogandaresi, which has a wide distribution that extends from Galveston Bay (U.S.A.) in Gulf of Mexico to Atlantic and Pacific slopes associated with poeciliid and cichlid fishes. New morphological data derived from scanning electron microscopy photographs of the body surface show a characteristic pattern of spination that is useful to distinguish between S. cichlidorum n. comb. and S. sogandaresi.

Microhabitat Selection and Eyefluke Infection Levels in the Western Mosquitofish (Gambusia affinis).

Several trematode species infect the eyes of fish as second intermediate hosts. In most cases the definitive host is a piscivorous bird. Studies of a few species have shown an increase in transmission due to decreased visual acuity of the fish host. However, this may vary depending on trematode microhabitat choice within the eye. Some trematode species are found in the lens, some are found in the vitreous humor, and others have been reported from the retina. Here we report 3 genera of eyeflukes in 3 locations of the eye in the intermediate fish host, Gambusia affinis . Clinostomum metacercariae were found attached to the outer sclera within the eye orbit, and Diplostomum metacercariae were found in the lens. Posthodiplostomum metacercariae were confirmed by histology to reside between the choroid and pigmented retina. Posthodiplostomum metacercariae were found in both eyes of all 20 fish examined and in high intensities (up to 27 metacercariae per eye). High trematode intensities between the choroid and pigmented retina found in this study may disrupt vision in this fish host. Our study is the first to document the microhabitat of all 3 trematode metacercariae within the eye of G. affinis .

ECHINOCHASMUS, NEW SPECIES (TREMATODA: ECHINOSTOMATIDAE) FROM EGYPT.

In this study a new species of Echinochasnius (Dietz, 1909) is recorded for the first time in Egypt. Life cycle of one of gymnocephalous cercariae procured from Melanoides tuberculata snail was successfully completed in the laboratory. A total of 407 Melanoides tuberculata snails were collected from Mansouriya Canal, Giza Governorate. They were individually exposed to artificial light to determine natural infection with trematode larvae, Seven snails were found infected with gymnocephalous cercariae (infection index of 1.71). These cercariae were used to infect Gambusia affinis fish as second intermediate host. The infected gills were given to clean laboratory bred Rattus norvegicus as experimental final host. Adult worms were obtained ten days post-infection from rats' intestine identified as Echinochasmus after accurate comparson with standard keys. The diagnostic morphology of developmental stages were given.

To each his own: no evidence of gyrodactylid parasite host switches from invasive poeciliid fishes to Goodea atripinnis Jordan (Cyprinodontiformes: Goodeidae), the most dominant endemic freshwater goodeid fish in the Mexican Highlands.

BACKGROUND: Goodeid topminnows are live-bearing fishes endemic to the Mexican Highlands (Mesa Central, MC). Unfortunately, in the MC, environmental degradation and introduced species have pushed several goodeid species to the brink of extinction. Invasive fishes can introduce exotic parasites, and the most abundant goodeid, blackfin goodea Goodea atripinnis Jordan, is parasitised by six exotic helminths. Poeciliids are widely dispersed invasive fishes, which exert negative ecological effects on goodeids. Poeciliids host several species of the monogenean genus Gyrodactylus von Nordmann, 1832, including pathogenic, invasive parasites. Here, we looked for evidence of Gyrodactylus species switching hosts from poeciliids to goodeids. METHODS: Fish were collected in rivers draining the MC into both sides of the continental divide. Hosts were screened for gyrodactylid parasites in localities where G. atripinnis and poeciliids occurred sympatrically. Gyrodactylus specimens were characterised morphologically (attachment apparatus) and molecularly (internal transcribed spacer region, ITS). A Bayesian phylogenetic tree using ITS sequences established relationships between gyrodactylids collected from goodeid fishes and those from parasites infecting poeciliids. RESULTS: Gyrodactylids were collected from G. atripinnis in six localities on both sides of the watershed where exotic poeciliids occurred sympatrically. Morphological and molecular analyses indicated the presence of four undescribed species of Gyrodactylus infecting this goodeid host. Gyrodactylus tomahuac n. sp., the most abundant and geographically widespread species, is described here. The other three Gyrodactylus spp. are not described, but their ITS sequences are used as molecular data presented here, are the only available for gyrodactylids infecting goodeid fishes. Morphological and molecular data suggest that two distinct groups of gyrodactylids infect goodeids, one of which shares a common ancestor with gyrodactylids parasitizing poeciliids. CONCLUSIONS: No evidence was found of gyrodactylids switching hosts from invasive poeciliids to endemic goodeids, nor vice versa. Moreover, considering that G. atripinnis is known to host both Gyrodactylus lamothei Mendoza-Palmero, Sereno-Uribe & Salgado-Maldonado, 2009 and Gyrodactylus mexicanus Mendoza-Palmero, Sereno-Uribe & Salgado-Maldonado, 2009, with the addition of G. tomahuac n. sp. and the three undescribed Gyrodactylus spp. reported, at least six gyrodactylids may infect this host. This would make monogeneans the second most abundant parasite group infecting G. atripinnis, which to date is known to harbour 22 helminth species: nine digeneans, five nematodes, four cestodes, three monogeneans and one acanthocephalan.

The first record of Centrocestus formosanus (Nishigori, 1924) (Digenea: Heterophyidae) in Egypt.

The life cycle of Centrocestus formosanus (Digenea: Heterophyidae) was to be successfully completed in the laboratory in the present study. Hundreds of the thiarid snail, Melanoides tuberculata, were collected from the main water course Mansouriya Canal, Giza Governorate, Egypt. The snails were individually exposed to artificial light to determine possible infection with trematode larvae. Fifteen snails were found infected with opthalmopleurolophocercous cercariae (infection index of 1.97). These opthalmopleurolophocercous cercariae shedded from snails were collected and placed in an aquarium with fish intermediate host, Gambusia affinis, to obtain metacercariae encysted in the gills. The gills with metacercariae were fed to albino rats, Rattus norvegicus, to obtain the adult worms. Adult worms were recovered in the small intestine of rats at 7 days after infection and they were identified as Centrocestus formosanus based on the morphological characteristics and the comparison with the previous descriptions in the literature. They were small, 518 × 324 µm in average size and had characteristic 32 circumoral spines around the oral sucker. The morphological characteristics of the developmental stages, from cercariae to adults, of this heterophyid fluke were given here. Therefore, the presence of this fluke is to be confirmed for the first time in Egypt by the present study.