Hemiuroidean trematodes from freshwater Patagonian fishes: description of a new species, distribution and molecular phylogeny

Untangling the Derogenes varicus species complex in Scandinavian waters and the Arctic: description of Derogenes abba n. sp. (Trematoda, Derogenidae) from Hippoglossoides platessoides and new host records for D. varicus (Müller, 1784) sensu stricto

Several studies have shown that the euryxenic trematode Derogenes varicus (Müller, 1784) represents a species complex. Four lineages have been designated (DV1-4) with the DV1 clade corresponding to D. varicus sensu stricto. Herein, we investigate newly collected specimens of D. varicus sensu lato from Scandinavian and Arctic waters using integrative taxonomy. The trematodes were collected from Melanogrammus aeglefinus, Eutrigla gurnardus, Trachinus draco, and Merluccius merluccius off the Atlantic coast of Sweden and from Hippoglossoides platessoides from Arctic Svalbard. 28S sequences of derogenids from Sweden were identical to D. varicus sensu stricto, confirming its euryxeny. The 28S sequences of Derogenes sp. from H. platessoides were identical to Derogenes DV2 and differed from D. varicus sensu stricto by 3% and from Derogenes DV3 by 2%. The 28S sequence divergences of Derogenes sp. from H. platessoides with D. ruber and D. lacustris were 3 and 10%, respectively. ITS2 and cox1 divergences between Derogenes sp. from H. platessoides and other Derogenes species/lineages were at levels of interspecific differences. The species from H. platessoides is described here as D. abba n. sp. We also examined the type material of Progonus muelleri (Levinsen, 1881), the type and only species of the genus Progonus, with redescription and designations of paralectotypes. Based on specimens from Theodor Odhner's collections at the Swedish Museum of Natural History, SMNH, Stockholm, we provide novel morphological and anatomical data for D. varicus sensu lato species complex. Lastly, we investigated Arthur Looss's "lost collection" of Trematodes at the SMNH and characterised a putative species Derogenes sp. "limula".

Some trematodes including three new species from freshwater fishes of Venezuela

The present paper comprises a systematic survey of trematodes found in 13 species of freshwater fishes in Venezuela collected in 1992, 1996 and 2001. The following 15 trematode species were recorded: Adults: Genarchella venezuelaensis sp. n., Thometrema dissimilis sp. n., Megacoelium spinicavum Thatcher et Varella, 1981, Doradamphistoma bacuense Thatcher, 1999, Crassicutis cichlasomae Manter, 1936, Parspina carapo Ostrowski de Núñez, Arredonto et Gil de Pertierra, 2011, Phyllodistomoides hoplerythrini sp. n. Larvae (metacercariae): Clinostomatopsis sorbens (Braun, 1899), Clinostomum marginatum (Rudolphi, 1819), C. detruncatum Braun, 1899, Ithyoclinostomum dimorphum (Diesing, 1850), Odhneriotrema microcephala (Travassos, 1922), Tylodelphys sp., Posthodiplostomum sp., Sphincterodiplostomum sp. All these parasites are reported from Venezuela for the first time and many of these findings represent new host records. The new species G. venezuelaensis sp. n., T. dissimilis sp. n. and P. hoplerythrini sp. n. were collected from the accessory respiratory organ of Loricariichthys brunneus (Hancock) (Loricariidae), from the stomach of Hoplerythrinus unitaeniatus (Spix et Agassiz) (Erythrinidae) and from the intestine of H. unitaeniatus, respectively. All parasites are briefly described and illustrated and problems concerning their morphology, taxonomy, hosts and geographical distribution are discussed. Megacoelium spinispecum Thatcher et Varella, 1981 is considered a junior synonym of M. spinicavum Thatcher et Varella, 1981, and Crassicutis opisthoseminis Bravo-Hollis et Arroyo, 1962 as a junior synonym of C. cichlasomae Manter, 1936.

Integrative Taxonomy of Prosogonotrema bilabiatum Vigueras, 1940 (Digenea: Sclerodistomidae): A Parasite in Atlantic Spadefish Chaetodipterus faber (Broussonet, 1782) (Acanthuriformes: Ephippidae) from Brazil

OBJECTIVES

The present work aims to expand the knowledge of the digenean species Prosogonotrema bilabiatum (Sclerodistomidae), a parasite of Chaetodipterus faber (Acanthuriformes) from Brazil, with an integrative taxonomic approach, using light microscopy, scanning electron microscopy, histology, and molecular biology.

METHODS

Forty-one digenean specimens were stained with hydrochloric carmine for morphological studies. Eleven parasites were dehydrated through a graded ethanol series, critical point dried with carbon dioxide, and coated with gold for scanning electron microscopy analysis. Four specimens were processed following histological routine and stained with hematoxylin and eosin and Gomori trichrome. DNA extracted was amplified using 28S partial primer D1-D3. Maximum likelihood and Bayesian inference were performed for phylogenetic analysis.

RESULTS

Morphometric and morphological data of the specimens studied ranged in accordance as observed in previous descriptions of the species. Observations from scanning electron microscopy and histology corroborated with those observed in stained whole mounts. Molecular analysis showed that specimens of P. bilabiatum from Brazil clustered with another two sequences of this species from different hosts and localities, with a high node support value.

CONCLUSIONS

The integrative taxonomic approach allowed to record and describe new characteristics of P. bilabiatum related to the tegument, the structure and the arrangement of its tissues. The use of molecular markers confirmed that specimens identified as P. bilabiatum from different hosts and localities are all conspecific. Further studies, mainly molecular with less conserved genetic markers, should be carried out to better understand the phylogenetic relationships of Prosogonotrema with Hemiuroidea.

Redescription and Molecular Characterisation of Derogenes ruber Lühe, 1900 (Hemiuroidea: Derogenidae) from Chelidonichthys lastoviza (Scorpaeniformes: Triglidae) in the Western Mediterranean

PURPOSE

Derogenes ruber Lühe, 1900, the type-species of the genus Derogenes Lühe, 1900, is a poorly known derogenid digenean. The original description of this species was not illustrated and aspects of the morphology of the parasite from the type-host remain scarce. Available records of this species were brief and/or lacked illustrations and were based on morphology alone. Additionally, molecular data for Derogenes spp. are warranted to untangle species complexes as they provide a better assessment of interspecific genetic divergence.

METHODS

Derogenes ruber is redescribed based on newly collected specimens from the gall bladder of its type-host Chelidonichthys lastoviza (Bonnaterre, 1788) collected in the Western Mediterranean off the Algerian coast during 2017-2019 and molecular data are provided using a partial fragment of the nuclear 28S ribosomal RNA gene (28S rRNA), the internal transcribed spacer 2 (ITS2) and a fragment of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene.

RESULTS

We herein provide a detailed illustrated redescription and morphometric data of D. ruber from its type-host C. lastoviza. We report a new geographical record (off Algeria) for it. Derogenes ruber is also genetically characterised for the first time. Species/lineages of Derogenes were recovered in five strongly supported reciprocally monophyletic clades: (i) D. ruber from C. lastoviza off Algeria; (ii) D. lacustris from Galaxias maculatus (Jenyns) off Argentina; (iii) Lineage "D. varicus DV1" (D. varicus sensu stricto) from fish hosts in the White and Barents seas and the North Sea; (iv) Lineage "D. varicus DV2" from mollusc hosts in the White Sea; and (v) Lineage "D. varicus DV3" from Eumicrotremus fedorovi Mandrytsa. in the Pacific Ocean. Hence, comparison of the newly generated sequences with other available data for Derogenes species supports the distinction of D. ruber confirming its taxonomic status and helping assess interspecific variation. Comparison of D. ruber with the closely related species Derogenes latus revealed overlaps in morphometric data and the validity of the latter species is questioned.

CONCLUSION

The combination of morphological and molecular data provided for D. ruber provides a firm foundation for further investigations of Derogenes spp. Although we do describe herein material of D. ruber from the type-host, given that the occurrence of a single Derogenes species in various hosts has been challenged by molecular data, and both D. lacustris and D. varicus sensu stricto had been genetically proven to occur in various hosts, D. ruber and D. latus may be indeed synonymous. Additional sequencing effort on Derogenes spp. will strengthen systematic comparative studies and evolutionary relationships within the Derogenidae in general.

Morphological and molecular characterization of Stomachicola muraenesocis Yamaguti, 1934 (Digenea: Hemiuridae) from the daggertooth pike conger Muraenesox cinereus (Forsskål)

Hemiurid digeneans conspecific with Stomachicola muraenesocis Yamaguti, 1934 (the type species of the genus Stomachicola Yamaguti, 1934) were collected from the stomach of the daggertooth pike conger Muraenesox cinereus (Forsskål) off the Persian Gulf of Iran. This study aimed to provide a detailed characterization of Stom. muraenesocis, including measurements, illustrations and scanning electron microscopy (s.e.m.) representations. Comparisons with the original and previous descriptions revealed morphological and metrical variations in several features (i.e. body size and shape, arrangement of reproductive organs, soma to ecsoma length ratio, position of genital opening, number of vitelline tubules and extension of uterine coils) between Stom. muraenesocis from different hosts and localities. This study presents the first molecular sequence data associated with the small (18S) and large (28S) subunit nuclear ribosomal RNA genes (rDNA) for Stom. muraenesocis. Phylogenetic analyses of the 18S dataset placed Stom. muraenesocis as sister lineage to a clade formed of a group of species of Lecithaster Lühe, 1901 (Lecithasteridae Odhner, 1905). In contrast, phylogenetic analyses based on the 28S consistently recovered a sister relationship between Stom. muraenesocis and representatives of the Hemiuridae Looss, 1899. Further comprehensive phylogenetically based classification in light of morphology and taxonomic history of the Hemiuridae and Lecithasteridae is required to infer phylogenetic affinities and historical biogeography of Stomachicola. A comprehensive list of previously reported species of Stomachicola together with their associated hosts, localities and morphometric data is provided.

A regional scale study of parasites in Percichthys trucha, an endemic fish of southern South America: insights on diversity and distribution from two decades of field surveys

The current conservation status of Percichthys trucha (Creole perch) is Least Concern, although the population trend is considered to be decreasing. We conducted an extensive survey of parasite fauna in this species over two decades in its distribution range in Argentina. Fish were collected using gill and trawl nets. Parasites were collected, identified, and counted to calculate prevalence and mean intensity. The present work reports the parasite species infecting P. trucha, using data from our own survey and from previously published records. This information enables us to evaluate infection and distribution patterns, assess the role of P. trucha as host, determine the specificity of the parasites, and evaluate the threat represented by introduced, invasive parasites. The data set consists of a total of 453 host-parasite-locality records, of which only 15 are exclusively bibliographic. We found 44 parasite taxa: 19 digeneans, 4 monogeneans, 5 cestodes, 8 nematodes, 4 acanthocephalans, 3 crustaceans, and 1 mollusk. The most represented families were Diplostomidae, Heterophyidae, and Dactylogyridae. This study increases the number of parasite species known from 25 to 44. It can be concluded that this parasite fauna is characterized by high diversity, particularly of digeneans, and most of the parasites reproduce within this host, a pattern which is related to the top position of this fish species in the trophic webs. Six parasite species (Allocreadium patagonicum, Homalometron papilliferum, Acanthostomoides apophalliformis, Duplaccessorius andinus, Pseudodelphys limnicola, and Hysterothylacium patagonense) exhibit high host specificity (only matures in Creole perches) and are widely distributed, which could now be considered as "biogeographical core helminth fauna." Some P. trucha populations are affected by the invasion of alien fishes like Cyprinus carpio and pathogenic parasites like Lernaea cyprinacea and Schizocotyle acheilognathi. Our findings emphasize the need for further research.

Hidden in the fog: morphological and molecular characterisation of Derogenes varicus sensu stricto (Trematoda, Derogenidae) from Sweden and Norway, and redescription of two poorly known Derogenes species

Derogenes varicus (Müller, 1784) is widely reported as a trematode with exceptionally low host specificity and a wide, bipolar distribution. However, several recent studies have suggested that D. varicus represents a species complex and based on molecular evidence, four genetic lineages (labeled as "DV1-4") have been designated within the D. varicus species complex. This possibility requires improved (ideally molecular) characterisation of specimens from the type-host (Salmo salar) and type-locality (off Denmark). During examination of trematode parasites of fish from Scandinavian and Arctic waters (Sweden and Norway), we found specimens of D. varicus in the stomach of Merlangius merlangus off the coast of Sweden, and in Gadus morhua off the coast of Sweden and Norway; we compared them to D. varicus from the type-host, the Atlantic salmon Salmo salar from Norway, to verify their conspecificity. Newly generated sequences (28S rDNA, ITS2 and cox1) of Scandinavian and Arctic specimens consistent with D. varicus all formed a single clade, DV1. 28S sequences of D. varicus from S. salar from Norway, i.e., close to the Danish type locality, clustered within the DV1 clade along with sequences of D. varicus from various hosts including Limanda limanda, G. morhua and Myoxocephalus scorpius from the White Sea and the Barents Sea (Russia), without any host-related structuring. We thus consider that the lineage DV1 represents D. varicus sensu stricto. Additionally, specimens from M. merlangus had a similar morphology and anatomy to those of D. varicus from L. limanda, G. morhua and M. scorpius from T. Odhner's collection, supporting the presence of a single species in the DV1 lineage designated herein as D. varicus sensu stricto. We redescribe D. varicus sensu stricto, add new morphological characters and provide morphometric data. We infer that D. varicus types DV2-4 all relate to separate species. We also revise type-specimens of Derogenes minor Looss, 1901 from the A. Looss collection in the Swedish Museum of Natural History and provide redescriptions of it and of the type-species of the genus, Derogenes ruber Lühe, 1900. In light of their morphological distinctiveness relative to D. varicus sensu stricto, we reinstate D. parvus Szidat, 1950 and D. fuhrmanni Mola, 1912.

Species complexes and life cycles of digenetic trematodes from the family Derogenidae

The best way to study digenean diversity combines molecular genetic methods, life-cycle studies and elaborate morphological descriptions. This approach has been barely used for one of the most widespread digenean taxa parasitizing fish – the superfamily Hemiuroidea. Here, we applied the integrative approach to the hemiuroideans from the family Derogenidae parasitizing fish at the White and Barents Seas. Analysis of 28S, 18S, 5.8S rDNA, ITS2 and cox1 gene sequences from sexually adult worms (maritae) showed genetic heterogeneity for 2 derogenid species known from this area: Derogenes varicus and Progonus muelleri. Thus, 2 pairs of genetic lineages were found: DV1 and DV2, PM1 and PM2, respectively. Data from other regions indicate that 2 more lineages of D. varicus probably exist. Based on previous records from the White and Barents Seas, we hypothesized that the cercariae found in the moonsnails (family Naticidae) belong to the Derogenidae and may help to differentiate these lineages as species. According to our results, Cercaria appendiculata from Cryptonatica affinis matched DV1, similar nameless cercariae from Euspira pallida and Amauropsis islandica matched DV2, and Cercaria octocauda from C. affinis matched PM1. We provide new data on the structure of these cercariae and discuss the life-cycle pattern of the studied digeneans.

First report of post-cyclic transmission in trematodes: Derogenes lacustris (Digenea: Hemiuroidea) in Patagonian freshwater fishes

The transmission of adult parasites from prey to predatory hosts has been demonstrated for some acanthocephalan and one cestode species. Derogenes lacustris (Digenea: Hemiuroidea: Derogenidae) is a generalist parasite that infects, as an adult, the stomach of native and introduced freshwater fishes in Andean Patagonia. In the present work, the post-cyclic transmission of D. lacustris from native Galaxias maculatus (Galaxiidae) to introduced Oncorhynchus mykiss (Salmonidae) was proved experimentally. The observed transmission rate for this experimental infection was 19%. The body length of D. lacustris on day 14 post-infection was significantly greater than before transmission. The number of eggs also increased significantly after transmission, showing that D. lacustris can survive, grow and continue with egg production for at least 2 weeks in predatory salmonids. This study provides the first experimental evidence of post-cyclic transmission of trematodes and the results suggest that post-cyclic parasitism enables this species to broaden its range of hosts and distribution ranges in Argentinean Patagonia.

A new species of hemiuroidean trematode from Hatcheria macraei (Siluriformes, Trichomycteridae) and Heleobia hatcheri (Gastropoda, Cochliopidae) in a Patagonian River

A new hemiuroidean species, Genarchella pichileufuensis n. sp. (Derogenidae: Halipeginae), was found in the stomach of the siluriform freshwater fish, Hatcheria macraei (Girard, 1855), in the Pichileufu River, Patagonia, Argentina. Its rediae with immature cystophorous cercariae were found in the snail Heleobia hatcheri (Pilsbry, 1911) in the same site. The present new species is morphologically featured by having a cyclocoel in the hindbody unlike the other species of the genus. The characteristics of this species allowed us to amend the diagnosis of the genus Genarchella as follows: cyclocoel present or absent; testes symmetrical to tandem; ootype pouch present. In the phylogenetic analysis, G. pichileufuensis forms a well-supported clade with Genarchella spp. recovered from Mexican freshwater fishes. This clade is included in the cluster of representatives of the subfamily Halipeginae. So far, three hemiuroidean species, Thometrema patagonica (Szidat, 1956), Derogenes lacustris Tsuchida, Flores, Viozzi, Rauque et Urabe, 2021 and G. pichileufuensis n. sp., have been reported from freshwater fishes in Argentinean Patagonia.