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Checklist of sharks, rays and chimaeras (Chondrichthyes, Elasmobranchii, Holocephali) from Mexico We present an annotated checklist of the species of sharks, rays and chimaeras (chondrichthyan fishes) occurring in Mexican waters, based on a thorough review of the literature and electronic database searches, examination of museum collection specimens, and unpublished records obtained during fieldwork conducted in the last four years. The checklist contains information of at least 214 species of chondrichthyan fishes that occur in Mexican marine and brackish waters, assigned to 84 genera, 40 families and 14 orders. It includes eight species of chimaeras, 95 batoids and 111 sharks. Condrichthyan fauna in Mexico is one of the richest in the world, with almost 17.3% of the known species. An additional 16 species are included as their occurrence in Mexican marine waters is probable according to distributional patterns.

Checklist of sharks, rays and chimaeras (Chondrichthyes, Elasmobranchii, Holocephali) from Mexico We present an annotated checklist of the species of sharks, rays and chimaeras (chondrichthyan fishes) occurring in Mexican waters, based on a thorough review of the literature and electronic database searches, examination of museum collection specimens, and unpublished records obtained during fieldwork conducted in the last four years. The checklist contains information of at least 214 species of chondrichthyan fishes that occur in Mexican marine and brackish waters, assigned to 84 genera, 40 families and 14 orders. It includes eight species of chimaeras, 95 batoids and 111 sharks. Condrichthyan fauna in Mexico is one of the richest in the world, with almost 17.3% of the known species. An additional 16 species are included as their occurrence in Mexican marine waters is probable according to distributional patterns. Data published through GBIF [doi:10.15470/hrl1kv]

Phyllodistomum pepirense n. sp. is described from the urinary bladder of Hoplias malabaricus (Bloch, 1794), sampled in the Jacaré-Pepira River in São Paulo state, Brazil. The isolates of the new species were recovered as a monophyletic group in the phylogenetic analysis of the 28S rRNA gene, which showed the new species as the sister taxa of Phyllodistomum virmantasi Pinacho-Pinacho, Sereno-Uribe, Hernández-Orts, García-Varela & Pérez-Ponce de León, 2021, a species sampled from an eleotrid fish in Southeastern Mexico. The new species differs morphologically from P. virmantasi by having a larger body size, slightly lobed testes and ovary, a mostly intercaecal uterus, slightly diverticulated caeca, and vitelline masses irregularly shaped. The new species is also readily distinguished from other species of Phyllodistomum Braun, 1899 reported from freshwater fishes in Brazil – namely, P. rhamdiae Amato & Amato, 1993 and P. spatula Odhner, 1902. The new species is herein described based on morphological characteristics, molecular data from D1–D3 domains of the 28S rRNA gene, host association, and geographical distribution. [ABSTRACT FROM AUTHOR]

Summary: Scaphanocephalus is a small trematode genus belonging to the family Opistorchiidae. The genus currently contains only three species associated with marine fish as intermediate hosts and fish-eating birds as definitive hosts. Here, specimens of Scaphanocephalus were collected from the Osprey, Pandion haliaetus , and the White mullet, Mugil curema in the Yucatán Peninsula, Mexico. We report for the first-time DNA sequences of adult specimens of Scaphanocephalus , particularly S. expansus , as well as a sequence of a different species sampled as metacercaria. Morphological comparisons of Scaphanocephalus expansus confirmed the identity of the adult specimens, with minor morphological variations; Scanning electron photomicrographs were included, and the species was re-described. Phylogenetic analysis based on 28S rDNA sequences showed that Scaphanocephalus is monophyletic within Opisthorchiidae and consists of three independent lineages. Sequences of adults are identical to those of S. expansus. Instead, the sequence of the metacercaria sampled from the mesentery of Mugil curema nested with specimens reported as Scaphanocephalus sp. from a labrid fish in the Mediterranean Sea, herein named it as Scaphanocephalus sp. 2. [ABSTRACT FROM AUTHOR]

Among fish parasitic nematodes Rhabdochona is one of the most speciose genera, with c. 100 species. Twelve congeneric species occur in Mexican freshwater fishes, in a region located between the Nearctic and Neotropical biogeographical regions. Host association and biogeographical history have determined the high species richness of Rhabdochona in Mexico. One of these species, Rhabdochona mexicana , is highly specific to the characid genus Astyanax. Characids are a group of freshwater fish with Neotropical affinity. In this paper, we explore the genetic diversity of R. mexicana through samples obtained from populations of Astyanax spp. across river basins of Mexico and Guatemala. Sequences of one mitochondrial and two ribosomal genes were obtained from 38 individuals and analysed using Maximum Likelihood and Bayesian Inference analysis. Phylogenetic analyses using cox 1, and a concatenated alignment of 18S + 28S + cox 1 recovered two genetic lineages. One of them corresponded with R. mexicana sensu stricto ; this lineage included three reciprocally monophyletic subgroups; the other lineage was highly divergent and represented a putative candidate species. A detailed morphological study was conducted to corroborate the molecular findings. We describe a new species herein and discuss the implications of using molecular tools to increase our knowledge about the diversity of a speciose genus such as Rhabdochona. [ABSTRACT FROM AUTHOR]

Neoechinorhynchus is one of the most speciose genera of acanthocephalans, with approximately 116 described species. A recent study, aimed at establishing the genetic diversity of Neoechinorhynchus in Middle American freshwater fishes, validated nine species molecularly and morphologically and revealed the existence of 10 putative candidate species. Neoechinorhynchus golvani , a parasite commonly found in cichlids throughout Middle America with an allegedly large intraspecific morphological variability, was found to represent a species complex; species delimitation methods uncovered three additional genetic lineages. Here, we re-analyse the morphological and molecular data for N. golvani species complex infecting cichlids in that geographical area. A multivariate analysis of variance (MANOVA) was conducted particularly for the length of apical, middle and posterior hooks of the species/lineages of Neoechinorhynchus in cichlids, revealing morphological variation in the length of apical hooks for Lineage 8, although no morphological distinction was observed for Lineages 9 and 10. A new concatenated phylogenetic analysis of one mitochondrial and two ribosomal DNA genes was used to further corroborate the species delimitation among lineages; Neoechinorhynchus Lineage 8 was found to be morphologically and genetically distinct from its sister taxa, N. golvani and other two undescribed genetic lineages, and is formally described as a new species. Neoechinorhynchus costarricense n. sp. is described from the intestines of eight species of cichlids in Costa Rica. The new species is distinguished from the other species/lineages of Neoechinorhynchus in cichlids mainly by the size of the apical hooks of the proboscis. [ABSTRACT FROM AUTHOR]

The family Clinostomidae Lühe, 1901 contains 29 species allocated to seven genera, of which Clinostomum Leidy, 1856 is the most diverse, with c. 14 valid species. The diversity of Clinostomum has been assessed, combining morphological and molecular data. The genetic library for species in this genus has increased steadily, although there is little or no information for the other genera included in the family. Molecular phylogenetic relationships among the genera of clinostomids have not been assessed, and their classification is still based on morphological traits. The monotypic Ithyoclinostomum was described from a fish-eating bird in Brazil, and its metacercariae have been found in several locations in South America, parasitizing erythrinid freshwater fishes. We collected unusually large metacercariae from the body cavity of cichlids in several locations across Middle America. These metacercariae exhibited some resemblance to Ithyoclinostomum , although several differences prevent their inclusion in Ithyoclinostomum dimorphum , casting doubt on their taxonomic identification. The main objective of this paper was to characterize the metacercariae collected in cichlids using both morphology and molecular data from three molecular markers, and to assess the molecular phylogenetic relationships among the genera of Clinostomidae to establish the position of the newly generated sequences. We took a conservative position and tentatively placed the metacercariae as belonging to Ithyoclinostomum. [ABSTRACT FROM AUTHOR]

Members of the genus Uvulifer are distributed worldwide and infect aquatic snails and freshwater fishes as first and second intermediate hosts, respectively, and fish-eating birds (kingfishers) as definitive hosts. Metacercariae of Uvulifer spp. were collected from the fins and skin of 20 species of freshwater fishes in Mexico, Guatemala, Honduras, Nicaragua and Costa Rica, and the adults were recovered from the intestine of kingfishers in four localities of Mexico. The genetic divergence among 76 samples (64 metacercariae and 12 adults) was estimated by sequencing the 28S and 5.8S nuclear genes, as well as the internal transcribed spacers ITS1 and ITS2, and one mitochondrial gene (cox 1). Maximum likelihood and Bayesian inference analyses inferred with each dataset showed a high genetic diversity within the genus Uvulifer across Middle America, revealing the existence of four genetic lineages that exhibit some level of host specificity to their second intermediate hosts. The metacercariae of lineage 1 were associated with characids and cyprinids in central and northern Mexico. Metacercariae of lineages 2 and 3 were associated with cichlids distributed widely across Middle America. The lack of adults of these lineages in kingfishers, in lineages 2 and 3, or the fact that just a few adult specimens were recovered, as in lineage 1, prevented a formal description of these species. The metacercariae of lineage 4 were found in poeciliids, across a distribution range comprising Mexico, Guatemala, Honduras and Nicaragua, and the adult was found in the green kingfisher in Mexico. The number of specimens sampled for lineage 4, for both gravid adults and metacercariae, allowed us to describe a new species, Uvulifer spinatus n. sp. We describe the new species herein and we discuss briefly the genetic diversity in Uvulifer spp. and the importance of using DNA sequences to properly characterize parasite diversity. [ABSTRACT FROM AUTHOR]

Members of the genus Drepanocephalus are endoparasites of fish-eating birds of the families Phalacrocoracidae and Sulidae distributed across the Americas. Currently, Drepanocephalus contains three species, i.e. D. spathans (type species), D. olivaceus and D. auritus. Two additional species, D. parvicephalus and D. mexicanus were transferred to the genus Petasiger. In the current study, available DNA sequences of D. spathans , D. auritus and Drepanocephalus sp., were aligned with newly generated sequences of D. spathans and Petasiger mexicanus. Phylogenetic analyses inferred with three nuclear (LSU, SSU and ITS1, 5.8S, ITS2) and two mitochondrial (cox 1, nad 1) molecular markers showed that the sequences of D. spathans and D. auritus are nested together in a single clade with very low genetic divergence, with Petasiger mexicanus as its sister species. Additionally, P. mexicanus was not a close relative of other members of the genus Petasiger, showing that P. mexicanus actually belongs to the genus Drepanocephalus, suggesting the need to re-allocate Petasiger mexicanus back into the genus Drepanocephalus , as D. mexicanus. Morphological observations of the newly sampled individuals of D. spathans showed that the position of the testes is variable and testes might be contiguous or widely separated, which is one of the main diagnostic traits for D. auritus. Our results suggest that D. auritus might be considered a synonym of D. spathans and, as a result, the latter represents a species with a wide geographic range across the Americas, parasitizing both the Neotropical and the double-crested cormorant in Argentina, Brazil, Paraguay, Venezuela, Colombia, Mexico, USA and Canada. [ABSTRACT FROM AUTHOR]

The Asian fish tapeworm, Schyzocotyle acheilognathi (syn. Bothriocephalus acheilognathi) represents a threat to freshwater fish, mainly cyprinids, across the globe. This tapeworm possesses an extraordinary ability to adapt to different environmental conditions and, because of that, from its natural geographical origin in mainland Asia, it has colonized every continent except Antarctica. It is thought that this pathogenic tapeworm was first co-introduced into Mexico in 1965 from China, with the grass carp Ctenopharyngodon idella, although the first formal record of its presence was published in 1981. Over the past 35 years, the Asian fish tapeworm has invaded about 22% of the freshwater fish in Mexico. Because fish communities in Mexico are characterized by high species richness and levels of endemism, S. acheilognathi is considered as a co-introduced and co-invasive species. In this review, we update the geographic distribution and host spectrum of the Asian fish tapeworm in Mexico. Up until December 2016, the tapeworm had been recorded in 110 freshwater fish species (96 native and 14 introduced), included in 51 genera, 11 families and 4 orders; it was also widely distributed in all types of aquatic environments, and has been found in 214 localities. We present novel data from a survey aimed at establishing the distribution pattern of the tapeworm in native freshwater fishes of two rivers in north-central Mexico, and the genetic variation among individuals of this co-invasive species collected from different host species and localities. We discuss briefly the factors that have determined the remarkable invasive success of this parasite in freshwater systems in Mexico. [ABSTRACT FROM AUTHOR]

We examine the extent to which adult helminths of freshwater fishes have been part of the Great American Biotic Interchange (GABI), by integrating information in published studies and new data from Panama with fish biogeography and Earth history of Middle America. The review illustrates the following: (1) the helminth fauna south of the Trans-Mexican Volcanic Belt, and especially south of the Isthmus of Tehuantepec, shows strong Neotropical affinities; (2) host–parasite associations follow principles of the ‘biogeographic core fauna’ in which host-lineage specificity is pronounced; (3) phylogenetic analysis of the widespread freshwater trematode family Allocreadiidae reveals a complex history of host-shifting and co-diversification involving mainly cyprinodontiforms and characids; (4) allocreadiids, monogeneans and spiruridan nematodes of Middle American cyprinodontiforms may provide clues to the evolutionary history of their hosts; and (5) phylogenetic analyses of cryptogonimid trematodes may reveal whether or how cichlids interacted with marine or brackish-water environments during their colonization history. The review shows that ‘interchange’ is limited and asymmetrical, but simple narratives of northward isthmian dispersal will likely prove inadequate to explain the historical biogeography of many host–parasite associations in tropical Middle America, particularly those involving poeciliids. Finally, our study highlights the urgent need for targeted survey work across Middle America, focused sampling in river drainages of Colombia and Venezuela, and deeper strategic sampling in other parts of South America, in order to develop and test robust hypotheses about fish–parasite associations in Middle America. [ABSTRACT FROM PUBLISHER]

Tylodelphys aztecae n. sp. (Digenea: Diplostomidae) is described from adult specimens obtained from the intestine of the pied-billed grebe (Podilymbus podiceps) and the metacercariae found in the body cavity of freshwater fishes of the families Goodeidae and Cyprinidae in eight localities across central and northern Mexico. The new species is mainly distinguished from the other four described species of Tylodelphys from the Americas (T. adulta, T. americana, T. elongata and T. brevis) by having a forebody slightly concave, a larger ventral sucker, two larger pseudosuckers and by having between 2 and 7 eggs in the uterus. Partial DNA sequences of the mitochondrial gene cytochrome c oxidase subunit I (cox1), and the internal transcribed spacers (ITS1+5.8S+ ITS2) of the ribosomal DNA, were generated for both developmental stages and compared with available sequences in GenBank of other congeners. The genetic divergence estimated among Tylodelphys aztecae n. sp. and other congeneric species varied from 12 to 15% for cox1, and from 3 to 11% for ITS. In contrast, the genetic divergence among metacercariae and adults of the new species was very low, ranging between 0 and 1% for cox1 and between 0 and 0.3% for ITS. Phylogenetic analyses inferred with both molecular markers using maximum likelihood and Bayesian inference placed the adults and their metacercariae in a single clade, confirming that both stages are conspecific. The morphological evidence and the genetic divergence, in combination with the reciprocal monophyly in both phylogenetic trees, support the hypothesis that the diplostomids found in the intestines of the pied-billed grebe bird and the body cavity from goodeid and cyprinid fishes in central and northern Mexico represent a new species. [ABSTRACT FROM AUTHOR]

The diplostomid genus Austrodiplostomum currently contains two species, i.e. A. mordax and A. ostrowskiae. Adults of these species inhabit the intestine of cormorants of the genus Nannopterum, whereas larval forms (metacercariae) are found in the eyes (vitreous humor) of freshwater fishes. Records of both species have been established across a wide geographic range in the Americas. Diplostomid adults and metacercariae were collected from a wide geographical range that spans from south-eastern Mexico, southwards to Central and South America. Even though the diplostomid has been largely reported in Mexico as Diplostomum (Austrodiplostomum) compactum, our specimens were identified morphologically as A. ostrowskiae. Sequences of the mitochondrial gene cytochrome c oxidase (cox 1) were obtained for 86 individuals, including 15 adults recovered from the intestine of Nannopterum brasilianus, in five localities, and 71 metacercariae from the eyes of ten fish species, in 13 localities. Sequences were used to evaluate the genetic diversity, and to test conspecificity of these specimens with the available sequence of A. ostrowskiae. Sequences were aligned with another 12 taxa representing five genera of Diplostomatidae, forming a dataset of 104 taxa with 478 nucleotides. The genetic divergence estimated among the 86 sequenced individuals, and that of A. ostrowskiae from the double-crested cormorant, Nannopterum auritus, in the USA, was very low, ranging from 0 to 0.8%. The maximum likelihood (ML) and Bayesian consensus trees showed that all sequences nested within a monophyletic lineage, with strong bootstrap and Bayesian posterior probability support values (100/1.0). In conclusion, a link between the metacercariae in fish and the adults in cormorants was established, indicating also that a single species is found in the distribution range comprising southern USA, southwards to Venezuela. Previous records of this species, particularly from Mexico, need to be corrected. [ABSTRACT FROM AUTHOR]

In parasitic organisms, particularly helminths, the usage of the mitochondrial cytochrome c oxidase subunit I gene as the standard DNA barcoding region for species identification and discovery has been very limited. Here, we present an integrated study, based on both DNA barcoding and morphological analyses, for acanthocephalans belonging to the genus Polymorphus, whose larvae (cystacanths) are commonly found in the mesentery of freshwater fishes, while adults are found in the intestine of fish-eating birds. The alpha taxonomy of parasitic helminths is based on adult morphological traits, and because of that larval forms cannot be identified to species level based on morphology alone. DNA barcoding offers an alternative tool for linking larval stages of parasitic organisms to known adults. We sequenced cystacanths collected from freshwater fishes in localities across central Mexico and adults obtained from fish-eating birds, to determine whether they were conspecific. To corroborate the molecular results, we conducted a morphometric analysis with 'Proboscis profiler', which is a software tool developed to detect heterogeneity in morphologically similar acanthocephalans based on the multivariate statistical analysis of proboscis hook dimensions. Both sources of information indicate that cystacanths infecting freshwater fishes in central Mexico belong to a single species, Polymorphus brevis. [ABSTRACT FROM AUTHOR]

Describes the nematode Rhabdochona ahuehuellensis from the intestines of the freshwater fish, Ilyodon whitei in Mexico. Comparison with other Rhabdochona species; Differentiation of male and female morphology; Thick-walled prostom; Large conical teeth; Body length; Muscular esophagus; Presence of pairs of subventral preanal papillae in male tail; Ratio of left to right spicule length.

The helminthological record of the California halibut, Paralichthys californicus, in hstero de Punta Banda, Todos Santos Bay and San Quintin Bay, Baja California, Mexico, is described. A total of 102 halibut was analyzed and 14 helminth species were identified: six were adult trematodes (Stephanostomum dentatum, Criptogoniminae, Metadena magdalenae, Opegaster parapristipomatis, Parahemiurus merus and Tubulovesicula lindbergi);. six nematodes (Spirocamallanus pereirai, Philometra sp. and Hysterothylacium sp. in the adult stage, and Anisakis sp., Contracaecum sp. and Porrocaecum sp. as larvae); a cestode (Tetraphyllidea); and an acanthocephalan (Corynosoma strumosum) in the larval stage. At the three sites, Anisakis sp. larvae and the plerocercoids from the order Tetraphyllidea were important, due to their high valuesof abundance and prevalence. Anisakis sp. is important for humans, because of the risk it presents for contracting anisakiasis disease. [ABSTRACT FROM AUTHOR]