Parasites Of Freshwater Fishes Research Articles

Two new dactylogyrid species (Dactylogyroidea: Dactylogyridae), gill parasites of freshwater fishes from the Peruvian Amazon, including the proposal of Peruanella n. gen.

A new genus of dactylogyrid, Peruanella n. gen., is proposed to accommodate Peruanella madredediosensis n. sp. from Brachyplatystoma tigrinum (Britski) (Siluriformes: Pimelodidae) from the Madre de Dios River, in Puerto Maldonado City, Madre de Dios region, Peru. The new genus differs from Neotropical dactylogyrids by possessing a combination of the following features: (1) tandem gonads, (2) a tubular J-shaped MCO, (3) an accessory piece connected to the base of the MCO via a filament, (4) a midventral vaginal aperture, (5) anchors similar in shape, each with short roots, (6) straight and robust bars, and (7) equal hook, each with undilated shanks and a depressed thumb. A previously described species, Demidospermus aureagarciae Morey, Rojas, Dávila, Chu & De Pina, 2023 exhibits characteristics that are compatible with the diagnosis of the new genus; therefore, this species is transferred to the Peruanella n. gen. In addition, Jainus peruensis n. sp. is described from Brycon amazonicus (Spix & Agassiz) (Characiformes: Bryconidae). This new species, which is the first species of the genus described in Peru and the third species infecting a bryconid host, can be differentiated from all congeneric species due to: (1) a slender MCO forming a counterclockwise loop at the proximal end, (2) an unarticulated accessory piece with a scythe-shaped distal end, (3) a rod-shaped ventral bar with a medial projection, and (4) a V-shaped and grooved dorsal bar.

New records of a freshwater fish parasite <i>Argulus japonicus</i> (Branchiura: Argulidae) from northern Honshu, Japan, with a note on its occurrence in a brackish water lake

New records of a freshwater fish parasite <i>Argulus japonicus</i> (Branchiura: Argulidae) from northern Honshu, Japan, with a note on its occurrence in a brackish water lake

Freshwater fish parasites in Temengor, Chenderoh and Bersia reservoirs, Perak, Malaysia

Parasitic infection causes a decrease in wild fish population and financial losses in culture fish.Fundamental biological variables like fish parasite composition baseline data and fish hosts parasites interactions on fish parasites are needed in establishing a monitoring andmanagement system of these freshwater fishes to mitigate the possible adverse effect of theseparasitic diseases. There is no information about protozoa and myxozoa parasitic fauna of thefishes in River Perak reservoirs. The prevalence of freshwater fish parasites in Temengor, Bersia and Chenderoh Reservoirs, Perak was investigated for 23 months for fish parasites using standard parasitological techniques. A total of 32 species of parasites detected belonging to 8 major taxa: 2 species of protozoans, 2 species of myxozoa, 12 species of monogeneans, 3 species of digeneans, 4 species of nematodes, 3 species of acanthocephalans and 5 species of copepods. Balantidium sp., Henneguya sp., and Myxobulus sp. were newly recorded parasites species in the reservoirs. The prevalence of parasitic infection in the reservoirs were 51 % in Temengor, Bersia 61% and Chenderoh 65 %. The parasite diversity of the fish parasites per reservoir were moderate. The parasite with the highest prevalence rate was recorded in Paradiplozoon barbi (17.39 %). Eighteen fish species were infected with parasites out of the twenty-five species sampled from the reservoirs. The fish family Cyprinidae was the dominant and most parasitized fish family in the reservoirs.

An integrative taxonomy study reveals a rare new species of the genus Creptotrema (Trematoda: Allocreadiidae) in an endangered frog in South America.

During an ecological study with a near-endangered anuran in Brazil, the Schmidt's Spinythumb frog, Crossodactylus schmidti Gallardo, 1961, we were given a chance to analyze the gastrointestinal tract of a few individuals for parasites. In this paper, we describe a new species of an allocreadiid trematode of the genus Creptotrema Travassos, Artigas & Pereira, 1928, which possesses a unique trait among allocreadiids (i.e., a bivalve shell-like muscular structure at the opening of the ventral sucker); the new species represents the fourth species of allocreadiid trematode parasitizing amphibians. Besides, the new species is distinguished from other congeners by the combination of characters such as the body size, ventral sucker size, cirrus-sac size, and by having small eggs. DNA sequences through the 28S rDNA and COI mtDNA further corroborated the distinction of the new species. Phylogenetic analyses placed the newly generated sequences in a monophyletic clade together with all other sequenced species of Creptotrema. Genetic divergences between the new species and other Creptotrema spp. varied from 2.0 to 4.2% for 28S rDNA, and 15.1 to 16.8% for COI mtDNA, providing robust validation for the recognition of the new species. Even though allocreadiids are mainly parasites of freshwater fishes, our results confirm anurans as hosts of trematodes of this family. Additionally, we propose the reallocation of Auriculostoma ocloya Liquin, Gilardoni, Cremonte, Saravia, Cristóbal & Davies, 2022 to the genus Creptotrema. This study increases the known diversity of allocreadiids and contributes to our understanding of their evolutionary relationships, host-parasite relationships, and biogeographic history.

The efficacy of salt treatment for Dactylogyrus extensus (Monogenea) infection in Carp (Cyprinus carpio)

Salt is widely recommended as a cost-effective and readily available compound against freshwater fish parasites in aquaculture; however, a limited number of studies provide scientific evidence regarding the efficacy of salt use despite its frequent use as an anti-parasitic in fish culture. Dactylogyrus is a severe gill parasite, causing considerable losses in freshwater aquaculture. The current study aimed to evaluate the anti-parasitic efficacy of salt against Dactylogyrus extensus in Cyprinus carpio. In vitro, mortality of D. extensus showed time- and concentration-dependent patterns. In vivo, the anti-parasitic effectiveness of salt to D. extensus was assessed at 23.56% after exposure to salt at a concentration of 1.25 g/L for 10 min. Anti-parasitic efficacy of salt in short-term application in carp can be categorised between slight and mild against monogenean, D. extensus.

A new species of Urocleidoides Mizelle & Price, 1964 from the gills of Schizodon nasutus Kner, 1858 (Characiformes, Anostomidae) in southeastern Brazil.

Based on an integrative approach, this study describes a new species of Urocleidoides infesting Schizodon nasutus in the Paranapanema River basin, Brazil. The new species can be distinguished from its congeners by specific morphological features, including the shape of the male copulatory organ and accessory piece, the ventral bar shape, and the shape and size of the hooks. Molecular analyses, particularly of the 28S rDNA gene, suggest a close relationship between the new species and Urocleidoides paradoxus. The phylogenetic and taxonomic arrangement of Urocleidoides is discussed, as the analyses of the 28S rDNA and COI mtDNA resolved the genus as non-monophyletic, with Diaphorocleidus, Rhinoxenus, and Cacatuocotyle nested within it. Additional morphological and molecular data of other congeneric species are required to investigate the phylogenetic position and classification of Urocleidoides. This study underscores the significance of using integrative approaches in understanding host-parasite associations and phylogenetic relationships, contributing to the description of the freshwater fish parasite biodiversity in South America, particularly in the Paranapanema river basin.

Parasitic Helminths and Freshwater Fish Introduction in Europe: A Systematic Review of Dynamic Interactions

The introduction of non-native freshwater fish is a primary cause of aquatic biodiversity loss at global scale. Such introductions have a severe impact on freshwater ecosystems in terms of competition, predation, habitat alteration, genetic pollution and transmission of diseases and parasites. A systematic review was conducted on the helminths parasites of freshwater fish in the context of species introduction and a total of 199 publications were retrieved between 1969 and November 2022. Several scenarios may arise when a new fish species arrive in a recipient area. Non-native fish hosts can co-introduce their parasites without transmitting them to native fish (e.g., the case of North American Centrarchidae and their Monogenea parasites). Another possible outcome is the transfer of these parasites to the native fish fauna (spillover, e.g., the cases of the Nematoda Anguillicola crassus Kuwahara, Niimi & Itagaki, 1974 and the Monogenea Gyrodactylus salaris Malmberg, 1957). Reciprocally, non-native fish hosts may acquire parasites in their new distribution range whether these parasites are native or were previously introduced (e.g., the cases of Ponto-Caspian Gobiidae and the Chinese sleeper Perccottus glenii Dybowski, 1877). Acquired parasites can then be spilled back to the native fauna. This phenomenon is of particular interest when non-native fish hosts influence the dynamics of zoonotic parasites.

Discovery of a Digenean (Cryptogonimidae) Living in a Cleft-Lipped Goby, Sicyopterus cynocephalus (Teleostei: Gobiidae) from Ranongga Island, Solomon Islands: Analysis of Multiple Ribosomal DNA Regions.

This study results from a continued investigation of the occurrence and diversity of parasites of freshwater fish in the Solomon Islands. Thus, we revealed a new host as well as a new site of infection and a new geographical area for the cryptogonimid parasite, Stemmatostoma cribbi (Digenea: Cryptogonimidae). The cryptogonimid species was identified based on general morphology and on molecular data of metacercariae found in the gills of the cleft-lipped goby, Sicyopterus cynocephalus, from Ranongga Island, Western Province of the Solomon Islands. This is the first report of a Stemmatostoma sp. digenean parasitizing fish of the genus Sicyopterus in the Indo-Pacific region and the first report of S. cribbi infection in a fish from the Solomon Islands. Phylogenetic analysis performed by Bayesian inference and maximum likelihood confirmed the presence of the cryptogonimid in a well-supported subclade of Stemmatostoma spp.

Epicatechin gallate: A promising agent isolated from Sargentodoxa cuneata for the treatment of ichthyophthiriasis in goldfish (Carassius auratus)

Ichthyophthirius multifiliis is a pathogenic parasite of freshwater fish that threatens the sustainability of aquaculture industry globally. Our previous studies have identified Sargentodoxa cuneata ethanol extracts exhibited potent antiparasitic activity against I. multifiliis. However, the active ingredients in S. cuneata remain unknown. In this study, we isolated an active compound from S. cuneata by bioassay-guided fractionation and identified it as epicatechin gallate (ECG) by NMR, FT-IR and HR-MS spectroscopy. In vitro assays revealed that ECG was effective against all the free-living stages of I. multifiliis. ECG could cause 100% mortality of theronts at 0.3 mg/L within 30.6 ± 0.4 min, and terminate reproduction of protomonts and tomonts at concentrations of 2.0 and 10.0 mg/L, respectively. Morphologically, 2.0 mg/L ECG treatment for 2 h induced the loss of plasma membrane integrity and leakage of intracellular contents of the protomont. Moreover, an in vivo parasite‑goldfish infection model was applied to evaluate the efficacy of ECG on prevention and treatment of ichthyophthiriasis. The results showed that 2.0 mg/L ECG treatment for 12 days could cure goldfish ichthyophthiriasis and significantly increase the survival rate of the infected goldfish by 86.7%. Acute toxicity test revealed that ECG was relatively safe to goldfish, with a median lethal concentration (LC50) value of 63.7 mg/L, which was >30 times higher than effective concentration against I. multifiliis in vivo. Overall, our data indicated that ECG had the potential as a novel antiparasitic agent for the treatment of ichthyophthiriasis in aquaculture.

Morphological and molecular characterization of three new species of Gyrodactylus (Monogenea: Gyrodactylidae) infecting Sicydium salvini (Teleostei: Gobiidae) in Mexican rivers draining into the Pacific Ocean.

The genus Gyrodactylus von Nordmann, 1832 is one of the most diverse within the class Monogenea; it contains mainly parasites of freshwater and marine teleost fishes. Around 40 species of Gyrodactylus have been described from gobiid fishes; mainly in Europe, as only two species are known from the Americas. In this study, we describe three new gyrodactylids from the body surface and fins of the goby Sicydium salvini (Gobiidae, Sycydiinae), which has a wide distribution on the Pacific coast, from Mexico to Panama. We describe Gyrodactylus oaxacae n. sp., G. atoyacensis n. sp. and G. salvini n. sp. collected from rivers draining to the eastern Pacific in the state of Oaxaca, Mexico. Morphologically, G. atoyacensis n. sp. and G. salvini n. sp. are very similar, and both are easily differentiated from G. oaxacae n. sp. Phylogenetic hypotheses based on sequences of the Internal Transcribed Spacers (ITS1-5.8S-ITS2 rDNA) and the D2+D3 domains of the large ribosomal subunit (28S rDNA) support the erection of the three new taxa; and suggest that G. atoyacensis n. sp. and G. salvini n. sp. are sister species. These gyrodactylids are the first monogeneans described from gobies of the genus Sicydium in Mexico.

Freshwater fish parasite diversity in West Bengal – A review

Aquaculture has the potential to meet the need of growing demand of fish in an affordable price. But in capture and in culture fisheries the fishes face diseases that interfere in the production of fish. The occurrence of disease causes the reduced production in aquaculture or reduce the marketable value of fish because of change of flesh quality, thus hampering the production. Freshwater fishes whether they are cultured or wild face different types of diseases in their skin, gills, fins, blood, and internal organs. The parasites that cause the diseases may be protozoans or metazoans.The main protozoan freshwater fish diseases are ichthyophthiriasis, trichodiniasis, costiosis, chilodonellosis. The most common metazoan parasitic diseases of freshwater fishes are dactylogyrusis, gyrodactylosis, argulosis, myxosporidiasis, ligulosis, ergasilosis, lernaesis, etc. The focus of this review is to screen the research studies that takes place on freshwater fish parasites of West Bengal. The review also aims to study the diversity of freshwater fish parasites in West Bengal, so that it will helps the researcher to get an idea about the freshwater fish parasites and their mode of infection in the fishes. The research work that takes place in different regions of West Bengal. Some of them reveal new species of parasites in fishes. Protozoan, cnidarian, acanthocephalan, nematode, cestode, trematode, crustacean parasites are identified in freshwater fishes of West Bengal. Among the protozoans cailiates, flagellates are identified. Trichodinids are very common protozoan fish parasites in most districts. Parasites under genus Myxobolus, Dactylogyrus, Gyrodactylus, Argulus, Lernea are common among the metazoans.

The elucidation of the life cycle of Saccocoelioides nanii Szidat, 1954 (Digenea: Haploporidae) using molecular techniques.

In South America, the knowledge of trematode diversity parasitizing freshwater fishes is still scarce, as less than 5% of the freshwater fish fauna has been examined for parasites. A similar situation applies to studies on digenean life cycles, which have become increasingly rare. Among the digenean families parasitizing freshwater fishes in the region, Haploporidae is considered the richest in species diversity. However, information about the developmental stages of haploporid life cycles remains fragmentary. Particularly, in Argentina, nine cercariae attributed to the family Haploporidae have been described using morphological analysis, and only two life cycles of this family have been completely elucidated. In this study a new type of cercaria, morphologically assigned to the family Haploporidae and collected from the snail Heleobia parchappii (Cochliopidae) in Los Padres shallow lake, Buenos Aires province, was identified using morphological and molecular techniques. The molecular analysis, based on 28S and ITS2 sequences, revealed that the cercariae were 100% identical to adult specimens of Saccocoelioides nanii (Haploporidae) parasitizing the fish Prochilodus lineatus (Prochilodontidae) from Los Talas, Buenos Aires province. Our results not only provide information about the life cycle of S.nanii but also show that a molecular and morphological approach can be extremely useful in identifying the developmental stages of digeneans and elucidating their life cycles.

Discovery of a New Genus and Species of Allocreadiidae (Trematoda) in Mexico: Mesoamericatrema Magnisacculus n. Gen. n. Sp.

The trematodes of Allocreadiidae are mainly parasites of freshwater fish and the family contains 18 valid genera. Since 2004, 4 genera have been described in the Americas: Paracreptotrema, Paracreptotrematoides, Pseudoparacreptotrema and Auriculostoma, of which the latter was recently synonymized with Creptotrema by Franceschini et al., (2021). During a study in 2018 on fish parasites of Lacantún River, Chiapas, Mexico, allocreadiids were collected from the intestine of Atherinella alvarezi and morphological differences with other genera of the family were immediately noted. These differences were corroborated with molecular data and phylogenetic analyses, which indicated that it was a new genus and species. The objective of this study is to describe the new taxon, which we name Mesoamericatrema magnisacculus n. gen., n. sp. as well as to clarify its phylogenetic relationships, host specificity, and geographical distribution. For this, we carried out a meticulous study of the morphology and compared the new taxon with its congeners. We also obtained sequences of the 28S and ITS from the ribosomal RNA region that were used in generating molecular phylogenies and in calculating genetic distances with sequences of other species of Allocreadiidae available in the Genbank. The new genus is mainly characterized by having a very large cirrus sac in relation to the length of its body and nests in a clade that groups Creptotrema, Creptotrematina, Paracreptotrema, Paracreptotrematoides, Pseudoparacreptotrema and Wallinia, all of which have a Neotropical affinity in terms of their geographic and host distribution. Mesoamericatrema n. gen. is the fifth genus of Allocreadiidae to be described in the Americas since 2004, the third discovered in Mexico since 2016, and the first to be described as parasitizing Atheriniformes, which indicates that Middle America is a region where important speciation events have occurred in freshwater fish parasites.

Does the fish-infecting Trypanosoma micropteri belong to Trypanosoma carassii?

Recently, based on a limited morphological characterisation and partial 18S rRNA gene sequence, Jiang et al. (2019) described Trypanosoma micropteri Jiang, Lu, Du, Wang, Hu, Su et Li, 2019 as a new pathogen of farmed fish. Here we provide evidence based on the expanded sequence dataset, morphology and experimental infections that this trypanosome does not warrant the establishment as a new species, because it is conspecific with the long-term known Trypanosoma carassii Mitrophanow, 1883, a common haemoflagellate parasite of freshwater fish. The former taxon thus becomes a new junior synonym of T. carassii.

Is Water Pollution the Only Cause of Abnormalities of the Attachment Clamps of Monogeneans (Diplozoidae), a Parasite of Freshwater Fishes?

Is Water Pollution the Only Cause of Abnormalities of the Attachment Clamps of Monogeneans (Diplozoidae), a Parasite of Freshwater Fishes?

Assessment of genotoxicity induced by helminthes parasites in freshwater fishes of river Ganges

Several parasites have been shown to induce genotoxicity in humans and fish are important intermediate hosts for completing the life cycle of many parasites, posing a huge economic loss worldwide through the ecosystem food chain. In the present study, we assessed the genotoxic potential of helminth Rostellascaris sp. through a benchmark of comet assay and micronucleus (MNi) tests on the hepatocytes, muscle, and whole blood of infected fish Bagarius bagarius (Hamilton) collected from different sites of the river Ganges. The percentage of the mean tail length of the comet was 10.28±0.36 in the reticulocytes of the infected fish which was significantly (P ˂0.05) longer compared to the control (2.86±0.12). Similarly, a significantly (P ˂0.05) higher DNA damage was observed in hepatocytes of parasite-infected fish (12.15±0.24) when compared to the control (3.024±0.013). A comparatively higher DNA damage was observed in the hepatocytes than the reticulocytes, indicative of tissue-specific DNA damage as hepatocytes are the biomarkers of metabolic functions prone toward biotic stress. A higher induction of MN was observed in infested fish (0.18±0.07) as compared to the control. Our results suggest that parasites contribute to the induction of cellular and DNA damage in fish during the progression of the host-parasite interaction.

Length-Weight Relationship and the Distribution of Intestinal Helminth Parasites in Freshwater Fishes from Amansea and Ebenebe Rivers in Anambra State, Nigeria

Aims: The current study was carried out to evaluate the prevalence and distribution of intestinal helminths in freshwater fishes. 
 Study Design: The study was a survey done to establish the type of intestinal parasite found in freshwater fish in the rivers.
 Place and Duration of Study: The fish samples were collected from Amansea and Ebenebe Rivers from November 2021 to January 2022.
 Methodology: Intestinal parasites of three (3) fish species commonly found in these rivers (Parachanna obscura, Clarias gariepinus, and Ctenopoma kingsleyae) were examined. A comparative evaluation of the prevalence and distribution of the parasite was done in relation to their gender, location, weight, and length.
 Results: A total of 24 fish samples were collected in the Amansea River and 26 samples were collected in Ebenebe River. Seventeen (17) samples of P. obscura, 21 samples of C. gariepinus and 12 samples of C. kingsleyae caught with the cast nets of various mesh sizes and gill traps by artisanal fishermen in Rivers were bought early in the morning, transported to the Laboratory and identified based on morphological features. Out of a total of 50 fish sampled, 17 fishes (34% of the total sample) were infected by intestinal helminths. P. obscura had the highest parasite prevalence (47.06%) followed by C. gariepinus (42.86%). However, no parasite was recorded in C. kingsleyae. Prevalence of intestinal parasites in Ebenebe (18.00%) was higher than in Amansea (16.00) with a significant difference in prevalence (p<0.05), while parasite abundance was higher in Amansea (50.94%) than in Ebenebe (49.06%) with significant difference (p<0.05). Females had the highest prevalence (35.00%) against male fishes (33.33%) with no significant difference. A total number of 53 parasites belonging to 7 genera were recovered in this study. Parasites identified were nematodes: Procamallanus sp. (41.5%), Camallanus sp. (9.43%), Rhabdochona sp. (26.42%), Contracaecum sp. (7.55%), and Spinitectus sp. (5.66%); cestodes: Polyonchobothrium sp. (5.66%); and trematodes: Clinostomum sp (3.77%). The highest parasite abundance was recorded in Procamallanus sp. (41.5%), while Clinostomum sp had the least (3.77%).
 Conclusion: This study revealed that the prevalence of intestinal parasites in freshwater fish is relatively high. Therefore, fish consumers should subject the fish to proper processing before consumption as some of these parasites are of zoonotic importance.

Description of Myxobolus hoabinhensis n. sp. (Myxosporea: Myxobolidae), infecting the trunk muscles of goldfish Carassius auratus (Linnaeus, 1758) (Cypriniformes: Cyprinidae) in northern Vietnam.

During a survey of myxosporean parasites of freshwater fishes in northern Vietnam, myxospores resembling those of the genus Myxobolus (Myxosporea: Myxobolidae) were found in the trunk muscle of 6 out of 35 specimens (17.14%) of wild goldfish Carassius auratus (Cypriniformes: Cyprinidae). The mature spores were 12.0 ± 0.4 (11.4 - 12.6) µm long, 8.5 ± 0.2 (7.9 - 9.0) µm wide and 6.1 ± 0.2 (5.8 - 6.3) µm thick, containing two pyriform-shaped polar capsules unequal in size. The larger polar capsule was 7.6 ± 0.3 (7.1 - 8.4) µm long and 3.5 ± 0.1 (3.3 - 3.8) µm wide, and the smaller polar capsule was 6.2 ± 0.3 (5.5 - 6.7) µm long and 2.9 ± 0.2 (2.6 - 3.4) µm wide. Each polar capsule contained a polar filament with 3-5 coils. A phylogenetic analysis based on the small subunit rDNA (SSU rDNA) sequence revealed that this Myxobolus species forms a distinct branch in the phylogenetic tree sister to Myxobolus artus and Myxobolus cyprini, with DNA sequence similarity at 97.6% to M. artus and 97.5% to M. cyprini. A combination of the morphological characteristics and molecular data suggest that this is an undescribed species, and we propose the name Myxobolus hoabinhensis n. sp.

New cytogenetic data on Caryophyllaeus laticeps and Paracaryophyllaeus gotoi, parasites of evolutionary interest.

Caryophyllideans are intestinal parasites of freshwater fishes, occupying a basal position among the ‘true’ tapeworms. We performed detailed cytogenetic analyses of the well-known caryophyllidean species Caryophyllaeus laticeps. For comparison, we also examined for the first time the chromosomes of Paracaryophyllaeus gotoi, a specific parasite of loaches in China. Both species showed a diploid chromosome number of 2n = 20, n = 10m. Chromomycin A3 (CMA3)/diamidino-2-phenylindole (DAPI) staining performed for the first time in the class Cestoda revealed CMA3+/DAPI− bands in the pericentromeric regions of the short arms of chromosome pair no. 7 in the karyotype of C. laticeps. Fluorescence in situ hybridization with the 18S rDNA probe confirmed the presence of a single cluster of major rDNA near the centromere on a pair of small chromosomes in both species. These findings support the hypothesis that the ancestral state in the family Caryophyllaeidae is a single interstitial cluster of major rDNA genes and thus one nucleolar organizer region per haploid genome. Our results, which we presented together with literature data plotted on a phylogenetic tree, show stability of caryophyllidean karyotypes at the genus level, but showed differences between genera without a clear phylogenetic signal. The data allowed us to at least formulate a hypothesis about the ancestral haploid chromosome number of n = 10 for the family Caryophyllaeidae and possibly for the sister family Capingentidae. In addition, we compared two populations of C. laticeps from water bodies with different levels of polychlorinated biphenyl contamination, showing a slightly increased incidence of chromosomal abnormalities at the contaminated site.

A checklist of the parasitic nematodes of freshwater fishes from Argentina

An annotated checklist of the nematodes parasites of Argentinian freshwater fishes is presented. This review includes information for 42 taxa of parasitic nematodes from 56 species of freshwater fish hosts. Fourty nematode species have been reported as adults and two as larvae. Camallanidae was the nematode family with the highest number of taxa (12 species), followed by Cucullanidae (4 species) and Raphidascarididae (4 species and 1 at genus level). The larval nematode Contracaecum sp. was the parasite with the widest range of host species, follow by Spirocamallanus hilarii, Spirocamallanus inopinatus, and Camallanus corderoi. Of the 570 species of freshwater fishes reported in Argentina, only 65 (11.4 %) were recorded as hosts of nematodes. Most records were in Characiformes, Siluriformes and Galaxiiformes, which may reflects sampling effort, since its abundance and widely distributions across differents ichthyogeographic provinces of Argentina. Most sampling were done in Great River and Patagonian ichthyogeographic provinces. The small number of examined fish hosts and geographically biased studies may not reflect the real richness and distribution of these parasites. Other obstacles that also contributes to the lack of completeness of this checklist are the problems in the taxonomic validity of some nematode species, doubtful host identification, and poor taxonomic resolution for larval stages of nematodes. Therefore, it is strongly recommended to deposit voucher specimens, including also of the hosts in reference collection, as well as performing integrative studies to elucidate the real taxonomic identity of nematode larvae. This is the first compilation on the nematode parasites of freshwater fishes from Argentina, including three nematode taxa recorded for new host records and four from new localities. Despite this study is exhaustive, the knowledge about parasitic nematodes from Argentinian freshwater fishes is far from complete, since some hydrological basin mainly in Pampean and Andean Cuyan regions and some host families remain unexplored in terms of nematode parasite detection.