Cucullanus lithodorasi n. sp. (Nematoda: Cucullanidae), a parasite of Lithodoras dorsalis (Siluriformes: Doradidae) on the north coast of Brazil

Cucullanus lithodorasi n. sp. (Nematoda: Cucullanidae), collected from the intestine of Lithodoras dorsalis (Siluriformes) and waters of the north coast of Brazil is described based on light and scanning electron microscopic observations. The new species differs from its congeners in the number and arrangement of cloacal papillae: five precloacal pairs and five postcloacal pairs and presence of unpaired ventral papillae located slightly anterior to the cloaca. This is the third nominal species of the genus infecting fishes from brackish water from Brazil.

Infection status of masu salmon Oncorhynchus masou by the parasite Salmonema cf. ephemeridarum (Nematoda, Cystidicolidae)

Nematodes that parasitize salmonids are found in both seawater and freshwater. Unlike seawater species such as those in family Anisakidae, freshwater species have not been well studied. In particular, the influences of these nematodes on the body condition of salmonids remain unclear. We studied the effects of Salmonema cf. ephemeridarum on the body condition of masu salmon Oncorhynchus masou. We found a positive relationship between the number of parasites and fish fork length. In contrast, we found a negative relationship between the body condition (condition factor) of fish and the number of parasites. These results suggest that nematode infection could affect host energy reserves for future growth.

Occurrence and First Molecular Characterization of Spinitectus notopteri Karve et Naik, 1951, Infected Bronze Featherback (Notopterus notopterus) in India

PURPOSE

The nematode genus Spinitectus Fourment, 1883, comprises species that are mainly parasitic on freshwater and marine fishes. However, our knowledge of the distribution and molecular identification of Spinitectus spp. in the Indian region is rather limited. This study aims to fill this gap in our knowledge using molecular data as evidence for Spinitectus species characterization.

METHODS

Bronze featherback were obtained opportunistically from the fish markets of district Muzaffarnagar (29.4727° N, 77.7085° E), Uttar Pradesh, India. Nematode species collected from the gastrointestinal tract were characterized morphologically and molecularly. Partial sequences of the ribosomal 18S rRNA gene were used for molecular characterization of the present specimens.

RESULTS

The current study represented molecular analysis that determined the presence of the species Spinitectus notopteri Karve et Naik, 1951. The sequences obtained were closely related to representatives of the family Rhabdochonidae.

CONCLUSION

This first molecular exploration of S. notopteri Karve et Naik, 1951, in the GenBank database and for any species of Spinitectus from India indicates a lack of genetic data for parasitic nematodes.

Molecular characterization of a novel Spiruromorpha species in wild Chinese pangolin by mitogenome sequence analysis

Pangolins are susceptible to a variety of gastrointestinal nematodes due to their burrowing lifestyle and feeding habits, and few parasitic nematodes have been reported. Here, a Chinese pangolin with old wounds on its leg and tail was rescued from the Heyuan City, Guangdong Province. The cox1 and SSU rRNA of the worms from the intestine of the Chinese pangolin had the highest sequence identity of 89.58% and 97.95% to the species in the infraorder Spiruromorpha. The complete mitogenome of the worm was further assembled by next-generation sequencing, with a size of 13,708 bp and a GC content of 25.6%. The worm mitogenome had the highest sequence identity of 78.56% to that of Spirocerca lupi, sharing the same gene arrangement with S. lupi and some species in other families under Spiruromorpha. However, the mitogenome between the worm and S. lupi showed differences in codon usage of PCGs, sequences of NCR, and tRNA secondary structures. Phylogenetic analysis showed that the worm mitogenome was clustered with S. lupi in the family Thelaziidae to form a separate branch. However, it is still difficult to identify the worm in the family Thelaziidae because the species in the family Thelaziidae are confused, specifically S. lupi and Thelazia callipaeda in the family Thelaziidae were separated and grouped with species from other families. Thus, the parasitic nematode from the Chinese pangolin may be a novel species in Spiruromorpha and closely related to S. lupi. This study enriches the data on gastrointestinal nematodes in the Chinese pangolin.

Molecular species delimitation of marine trematodes over wide geographical ranges: Schikhobalotrema spp. (Digenea: Haplosplanchnidae) in needlefishes (Belonidae) from the Pacific Ocean and Gulf of Mexico

Geographical distribution plays a major role in our understanding of marine biodiversity. Some marine fish trematodes have been shown to have highly restricted geographical distributions, while some are known to occur over very wide ranges; however, very few of these wide distributions have been demonstrated genetically. Here, we analyse species of the genus Schikhobalotrema (Haplosplanchnidae) parasitizing beloniforms from the tropical west Pacific, the eastern Pacific and the Gulf of Mexico (GoM). We test the boundaries of these trematodes by integrating molecular and morphological data, host association, habitat of the hosts and geographical distribution, following a recently proposed and standardized delineation method for the recognition of marine trematode species. Based on the new collections, Schikhobalotrema huffmani is here synonymized with the type-species of the genus, Schikhobalotrema acutum; Sch. acutum is now considered to be widely distributed, from the GoM to the western Pacific. Additionally, we describe a new species, Schikhobalotrema minutum n. sp., from Strongylura notata and Strongylura marina (Belonidae) from La Carbonera coastal lagoon, northern Yucatán, GoM. We briefly discuss the role of host association and historical biogeography of the hosts as drivers of species diversification of Schikhobalotrema infecting beloniforms.

Three new species of Ascarophis van Beneden, 1871 (Nematoda: Cystidicolidae) from deep-sea hydrothermal vent fishes of the Pacific Ocean

Examinations of some deep-sea hydrothermal vent fishes from the western and eastern regions of the Pacific Ocean revealed the presence of three new species of Ascarophis van Beneden, 1871 (Nematoda: Cystidicolidae), all gastrointestinal parasites, namely: A. justinei n. sp. from Thermarces cerberus Rosenblatt & Cohen (type host) and Thermichthys hollisi Cohen, Rosemblatt & Moser (both Zoarcidae, Perciformes) and A. globuligera n. sp. from T. cerberus from the Northern East Pacific Rise, and A. monofilamentosa n. sp. from Pyrolicus manusanus Machida & Hashimoto (Zoarcidae, Perciformes) from the Manus Basin near Papua New Guinea. Specimens are described and illustrated based on light and scanning electron microscopical examinations. In addition to other morphological differences, all the three new species differ from each other by the structure of eggs: eggs bearing a lateral superficial swelling (A. globuligera n. sp.), eggs with one conspicuously long filament on one pole (A. monofilamentosa n. sp.) and eggs smooth, without any filaments or swellings (A. justinei n. sp.). The egg morphology of the two first-named species is unique within all species of Ascarophis, which indicates that all the three newly described species of Ascarophis are probably endemic to the respective hydrothermal vents as their fish hosts.

Redescriptions of Spinitectus acipenseri and S. micracanthus (Nematoda, Cystidicolidae), with notes on the taxonomy of Spinitectus-like nematodes parasitising North American fishes

Based on light microscopical and scanning electron microscopical (SEM) examinations, two North American species of Spinitectus Fourment, 1884, S. acipenseri Choudhury & Dick, 1992 and S. micracanthus Christian, 1972 (Nematoda, Cystidicolidae) are redescribed from museum voucher specimens (S. acipenseri) and those newly collected from centrarchid and some other fishes in the Upper San Marcos River in Texas and the Santee River in South Carolina, USA. The first use of SEM to study S. acipenseri, a parasite of lake sturgeon Acipenser fulvescens Rafinesque (Acipenseridae) in Canada, made it possible to describe dorsal and ventral lips, amphids and sublabia, and the presence of a dorsal barb on the right spicule, which was confirmed to be the most characteristic feature of this species. The SEM study of S. micracanthus, a parasite mainly of centrarchids, enabled us to correctly determine the location of the excretory pore in relation to rings of cuticular spines in the male, and to describe the exact structure of the tip of the male tail, sublabia, phasmids and the presence of a median ventral protuberance on the male tail. Some taxonomic problems of North American species of Spinitectus are discussed. Filaria serrata Linton, 1901 is considered a junior synonym of S. oviflagellis Fourment, 1884. To date, there are 13 valid species of Spinitectus parasitising fishes in North America. Keys to species of Spinitectus-like nematodes from fishes in North American waters are provided.

Integrated morphological and molecular characterization of the fish parasitic nematode Rhabdochona (Rhabdochona) gendrei Campana-Rouget, 1961 infecting Labeobarbus altianalis (Boulenger, 1900) in Kenya

During a parasitological survey carried out between May and August 2022 in the River Nyando, Lake Victoria Basin, a single species of Rhabdochona Railliet, 1916 (Nematoda: Rhabdochonidae) was recorded from the intestine of the Rippon barbel, Labeobarbus altianalis (Boulenger, 1900) (Cyprinidae). Based on light microscopy (LM), scanning electron microscopy (SEM) and DNA analyses the parasite was identified as Rhabdochona (Rhabdochona) gendrei Campana-Rouget, 1961. Light microscopy, SEM and DNA studies on this rhabdochonid resulted in a detailed redescription of the adult male and female. The following additional taxonomic features are described in the male: 14 anterior prostomal teeth; 12 pairs of preanal papillae: 11 subventral and one lateral; six pairs of postanal papillae: five subventral and one lateral, with the latter pair at the level of first subventral pairs when counted from the cloacal aperture. For the female: 14 anterior prostomal teeth and the size and absence of superficial structures on fully mature (larvated) eggs dissected out of the nematode body. Specimens of R. gendrei were genetically distinct in the 28S rRNA and cytochrome c oxidase subunit 1 (cox1) mitochondrial gene regions from known species of Rhabdochona. This is the first study that provides genetic data for a species of Rhabdochona from Africa, the first SEM of R. gendrei, and the first report of this parasite from Kenya. The molecular and SEM data reported herein provide a useful point of reference for future studies on Rhadochona in Africa.

First report of Metathelazia capsulata in red foxes (Vulpes vulpes) in Europe and new contributions to its identification

Metathelazia capsulata is a lungworm that inhabit in the bronchi and bronchioles from mammal carnivore species, which life cycle is unknown. M. capsulata-like spirurid nematodes were isolated at necropsy from the respiratory tract of red foxes (Vulpes vulpes) from the Region of Murcia (SE Spain). The main objective of this study was to describe in detail the morphometric features of these nematodes, as well as to report some molecular markers. The principal morphometric difference compared to previous M. capsulata descriptions was the shorter total length for both males and females (6.6 mm and 7.4 mm, respectively). In addition, the mean values of buccal cavity depth and distance between the excretory pore and the anterior end of the nematode were also lower than those previously reported. On the other hand, sequence data of the mitochondrial (COI) and nuclear (rDNA) genes of M. capsulata were described, being the first time that molecular markers are reported for the genus Metathelazia and also for the entire family Pneumospiruridae. Based on data available from GenBank, these results indicate that M. capsulata sequences are closely related to the family Rhabdochonidae, which is assumed to belong to superfamily Thelazioidea, a superfamily including the family Pneumospiruridae, but also suggest the distant relations with the family Thelaziidae. This is the first time that M. capsulata is reported in red fox from Europe. This study provides valuable information for future phylogenetic studies on Metathelazia spp. nematodes and, in general, on species of the family Pneumospiruridae.

Additional data on Spinitectus petterae (Nematoda: Rhabditida) from Clarias gariepinus (Siluriformes: Clariidae) in the Vaal River system: conserved morphology or high intraspecific genetic variability?

Two species of Spinitectus Fourment, 1884 have been recorded from southern Africa, namely Spinitectus polli Campana-Rouget, 1961 and Spinitectus petterae Boomker, 1993, both from the Limpopo River system. Spinitectus petterae was described from North African catfish, Clarias gariepinus (Burchell), whereas S. polli infects squeakers, Synodontis spp. During parasitological surveys in the Vaal River system (Orange River catchment), Spinitectus specimens were collected from C. gariepinus. These systems are adjacent but not connected. Therefore, this study aimed to identify the specimens collected using morphological and molecular techniques. The morphological study included light and scanning electron microscopy of whole specimens and excised spicules. Specimens were genetically characterised using 18S rDNA, 28S rDNA and cox1 mtDNA. Additionally, immature specimens of S. petterae were collected near the type locality. Morphological characteristics were most similar to S. petterae from C. gariepinus, whereas genetic data were dissimilar to all available data for the genus. Additional morphological characteristics noted for S. petterae in the present study were the details of the left and right spicule structure and the porous structures on the pseudolabia. Specimens from the Vaal River system differed from those originally described as S. petterae by additional spines posterior to the third ring, lacking caudal alae and variable total body and male oesophagus length. Based on 18S rDNA, haplotypes from the type locality varied only slightly from the study material, supporting the morphological identification. However, 28S rDNA and, more conspicuously, cox1 mtDNA displayed substantial variation between specimens from these localities, which needs further investigation. Haplotypes generated in the present study were highly dissimilar to those characterised for S. petterae from Tanzania and Egypt. Nevertheless, the nematodes collected from C. gariepinus in the Vaal River system are considered S. petterae. This study expands the geographical distribution and adds additional morphological and genetic information for S. petterae, contributing to the limited knowledge of African species of Spinitectus.

Review of the parasitic nematodes of marine fishes from off the American continent

The ichthyofauna of the Atlantic and Pacific coasts off the American continent is very rich. Consequently, a high biodiversity of nematodes parasitizing these vertebrates is also expected. Currently, data on nematode parasites of marine fish off the Americas are fragmented. A review of all adult nematode species reported parasitizing marine fish from off the American continent is herein presented, as well as comments on their patterns of diversity, life cycles and advances in the taxonomic and phylogenetic knowledge. A total of 209 valid species, 19 species inquirendae and 6 dubious records have been recorded, the majority from the fish taxa Eupercaria and Perciformes. The families Sciaenidae, Serranidae and Lutjanidae, as well as the tropical and temperate Atlantic waters, exhibited the highest records of parasitic nematodes. The Cucullanidae, Philometridae and Cystidicolidae were the most speciose families of nematodes, which may be related to technological advances and relatively recent efforts of taxonomists, resulting in description of new taxa and the resolution of taxonomic problems. Numerous taxonomic questions still need resolution and, even though genetic data have been important for this process, the database is very scarce. This is the first review on all currently known nematode species parasitizing marine fish off the Americas and may serve as an important basis of reference for future approaches on these organisms.

Assessment of Hydrobiological and Soil Characteristics of Non-Fertilized, Earthen Fish Ponds in Sindh (Pakistan), Supplied with Seawater from Tidal Creeks

In this study, the suitability of four earthen, seawater ponds located in the Thatta district of Sindh province (Pakistan) was evaluated for the purpose of semi-intensive mariculture, which remains to be a severely underdeveloped branch of the agricultural industry of this populous Asian country. Initial pond soil probes were promising, as they showed a high clay and silt content. Monthly water samples were obtained in the year 2019 (from January to December), which allowed for the monitoring of water parameters, as well as the identification and relative quantification of planktic populations. As a result, the monthly variations of basic water parameters were found within optimal ranges for planktic growth (water temperature, salinity, pH, transparency, and dissolved oxygen). Bacillariophyta was the largest phytoplanktic group, with the most dominant species being Sundstroemia setigera, followed by the cyanobacteria Oscillatoria limosa. Copepoda was the most numerous group of identified zooplankton, followed by tintinnids and foraminiferans. Total suspended solids (TSS) calculations indicated up to nine-fold month-to-month reductions of planktic biomass, observed in the form of diminishing Bacillariophyta (December) and Copepoda (June and December). In conclusion, the studied ponds appear to be suitable for semi-intensive mariculture activity due to the abundance of diverse planktic forms (mainly Copepoda—preferable natural food for commercially important fish species), which was achieved even without the use of fertilizers. However, significant drops of planktic biomass may still occur, which implies the need for regular water monitoring procedures, which would in turn allow fish producers to implement periodical adjustments to the administered feeding rates with artificial diets.

Genetic characterisation of Tanqua (von Linstow, 1879) (Nematoda: Gnathostomatidae) larval forms including new host and locality records

In an unrelated study of spotted snakehead fish Channa punctata (Bloch) of family Channidae (N = 103) from Bangladesh, ten fish had taupe and clear coloured cysts attached to the intestinal mesentery. Investigation of the cysts revealed larval nematodes. The larvae were damaged and not suitable for detailed morphological study, however, key features such as tooth like projections of the pseudolabia and lateral pseudolabium were observed in specimens with undamaged cephalic regions. Molecular characterisation was undertaken and although the parasite genetic material was poor, five of the twelve nematode larvae through sequencing of the 18S ribosomal RNA gene, showed 98.17% match with sequences assigned for Tanqua tiara (accession number JF934728) deposited in GenBank. The prevalence of infection was 9.7% and the mean intensity 2.70. Tanqua has not previously been identified in fish, or from the definitive host, the Asian water monitor Varanus salvator (Laurenti, 1768) of family Varanidae (class Reptilia), in Bangladesh. Therefore, this study represents a new host and locality record for this nematode species. In many previous reports from this region, nematode larvae have been identified morphologically and assigned to a diverse range of nematode genera. Some confusion therefore exists regarding their accuracy and further investigations are required using molecular methodology to clarify the species of larval nematodes which infect edible fish in Bangladesh.

•

Tanqua species identified from Channa punctata.

•

New host and region record for Tanqua species in Bangladesh.

•

Tanqua species identified using molecular methodology.

Morphology and phylogeny of the parasitic nematode Mooleptus rabuka (Machida, Ogawa & Okiyama, 1982) (Rhabditida, Spirurina: Mooleptinae nom. nov.), with notes on taxonomy of the family Gnathostomatidae

The nematode Mooleptus rabuka is recorded in the digestive tract of catshark Apristurus fedorovi caught at the Imperial Ridge (Pacific Ocean). Important morphological features such as the number of cephalic and caudal papillae, the position of amphids and the shape of the gubernaculum are detailed in this parasite species. According to the phylogenetic analyses based on the 18S ribosomal RNA gene sequences, M. rabuka forms a lineage, Mooleptinae nom. nov., which is close to the gnathostomatid genus Echinocephalus (maximum likelihood analysis), or else forms a polytomy with this genus and the lineages of Anguillicola + Spiroxys and Tanqua + 'Linstowinema' sp. (Bayesian inference analysis). Overall, our findings do not support the monophyly of the Gnathostomatidae. We elevate spiroxyines to the family status, Spiroxyidae stat. nov., and temporarily consider the Gnathostomatidae to include the following subfamilies: Ancyracanthinae Yorke & Maplestone, 1926, Gnathostomatinae Railliet, 1895 sensu lato and Mooleptinae nom. nov. The name Mooleptinae nom. nov. is suggested instead of the Metaleptinae Moravec & Nagasawa, 2000, which is based on a preoccupied generic name Metaleptus Machida, Ogawa & Okiyama, 1982.

A new species of Hedruris (Nematoda: Hedruridae) from freshwater turtles, its life cycle and biogeographic distribution of the genus

We describe Hedruris dratini n. sp. (Nematoda, Hedruridae) from Hydromedusa tectifera and Phrynops hilarii in Argentina based on morphological and molecular characters. Also, we provide information about its life cycle. The new species differs from other species of the genus by possessing the excretory pore, nerve ring and deirids at equal distance from the anterior end. Additionally, H. dratini n. sp. has mammilated eggs and males possess nine pairs of caudal papillae. The subadults and adults of H. dratini n. sp and H. orestiae were characterized by sequencing the small subunit ribosomal DNA (18S). We present for the first time a life cycle of a species of Hedruris that includes an amphipod as intermediate host and a reptile as definitive host. Furthermore, we analysed the host and geographic distribution of all Hedruris species. Although the genus has a cosmopolitan distribution and parasitizes a great host diversity, the majority of species have a Gondwanian distribution, with amphibians being the preferred hosts.

Diversity ofRhabdochona mexicana(Nematoda: Rhabdochonidae), a parasite ofAstyanaxspp. (Characidae) in Mexico and Guatemala, using mitochondrial and nuclear genes, with the description of a new species

Among fish parasitic nematodesRhabdochonais one of the most speciose genera, withc.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 ofRhabdochonain Mexico. One of these species,Rhabdochona mexicana, is highly specific to the characid genusAstyanax.Characids are a group of freshwater fish with Neotropical affinity. In this paper, we explore the genetic diversity ofR. mexicanathrough samples obtained from populations ofAstyanaxspp. 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 usingcox1, and a concatenated alignment of 18S + 28S +cox1 recovered two genetic lineages. One of them corresponded withR. 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 asRhabdochona.

Taxonomic status of Rhabdochona ictaluri (Nematoda: Rhabdochonidae) based on molecular and morphological evidence

The genus Rhabdochona includes more than 100 species infecting freshwater fishes in all zoogeographical regions of the world. In Mexico, 12 nominal species of Rhabdochona have been recorded. Of these, Rhabdochona ictaluri was originally described as a parasite of endemic catfishes of the family Ictaluridae; however, the species was later considered on morphological grounds as a junior synonym of Rhabdochona kidderi. In this study, newly sampled specimens of R. ictaluri were obtained from the type host and type locality and were used to perform a detailed morphological analysis and molecular phylogenetic inferences through one mitochondrial and two nuclear genes; data were used in an integrative taxonomy context to test the taxonomic status of R. ictaluri. This approach proved to be very useful to confirm the validity of this species, and robust species limits were established between these two putative species considering morphology, molecular data, host association, and biogeography.