Ecology and effects of metazoan parasites of fish in transitional waters.

Given the abundance, heterogeneity and ubiquity of parasitic organisms, understanding how they influence biodiversity, evolution, health and ecosystem functionality is crucial, especially currently when anthropogenic pressures are altering host­parasite balances. This review describes the features, roles and impacts of metazoan parasites of fish occurring in transitional waters (TW). These aquatic ecosystems are highly productive and widespread around the globe and represent most favourable theatres for parasitism given the availability of hosts (invertebrates, fishes and birds) and an increased probability of parasite transmission, especially of those having complex life cycles. Fascinating examples of how parasitism can influence different hierarchical levels of biological systems, from host individuals and populations to entire aquatic communities, through effects on food webs come from this kind of ecosystem. Edible fish of commercial value found in TW can harbour some parasite species, significantly reducing host health, marketability and food safety, with possible economic and public health consequences. Many TW are historically exploited by humans as sources of relevant ecosystem services, including fisheries and aquaculture, and they are highly vulnerable ecosystems. Alteration of TW can be revealed through the study of parasite communities, contributing, as bioindicators, for assessing environmental changes, health and restoration. Fish parasites can provide much information about TW, but this potential appears to be not fully exploited. More studies are necessary to quantify the ecological, economic and medical impacts fish parasites can have on these important ecosystems.

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

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

The description of two new species of Chloromyxum from skates in the Argentine Sea reveals that a limited geographic host distribution causes phylogenetic lineage separation of myxozoans in Chondrichthyes.

During a survey on the myxosporean fauna of Rajiformes from the Atlantic coast of Argentina, in waters off Buenos Aires Province (34°-42°S; 53°-62°W), the gall bladders of 217 specimens belonging to seven species of skates, representatives of two families, were examined. As a result, three species of Chloromyxum Mingazzini, 1890, namely C. atlantoraji n. sp., C. zearaji n. sp. and C. riorajum Azevedo, Casal, Garcia, Matos, Teles-Grilo and Matos, 2009 were found infecting three endemic host species, the spotback skate Atlantoraja castelnaui (Arhynchobatidae), the yellownose skate Zearaja chilensis (Rajidae) and the Rio skate Rioraja agassizii (Arhynchobatidae), respectively. These species were described based on myxospore morphology and morphometry characterization, as well as by providing their small subunit ribosomal DNA (SSU rDNA) sequences. The SSU rDNA-based phylogenetic analyses showed that these three species constituted a well-established monophyletic subclade within the marine Chloromyxum clade, while branches subtending the other Chloromyxum species were poorly resolved or unresolved, independently of the host taxonomic identities (Carchariniformes, Myliobatiformes, Orectolobiformes, Pristiophoriformes, Rajiformes, Squaliformes and Torpediniformes) and/or host geographic distribution (Atlantic coast of Portugal, Atlantic coast of the USA, Australian waters or Mediterranean Sea). The possible causes of these discrepancies are discussed, providing new insights into the phylogeny of the marine Chloromyxum clade.

Distribution of anisakid nematodes parasitizing rajiform skates under commercial exploitation in the Southwestern Atlantic.

In order to evaluate the infestation by anisakids present in elasmobranchs and their distribution in the Argentine Sea, this study was carried at a regional scale with the following aims: 1) to identify those anisakid species present in skates under exploitation; 2) to characterize quantitatively these infestations and 3) to determine those factors driving the variability in parasite burdens across skate species. A total of 351 skates, belonging to 3 species (218 Sympterygia bonapartii, 86 Zearaja chilensis and 47 Atlantoraja castelnaui) and from different localities of the Argentine Sea were examined for anisakids. Parasites were found in the stomach wall at high prevalence in some samples. Based on morphology and mtDNA cox2 sequences analyses (from 24 larval worms), specimens were identified as Anisakis berlandi, A. pegreffii and Pseudoterranova cattani; the last two known as potentially pathogenic for humans. Differential distribution patterns were observed across parasite and hosts species. In general, fish caught in southern and deeper waters exhibited higher loads of Anisakis spp., whereas infestation levels by P. cattani increase in larger skates. Taking into account that the mere presence of worms or their antigens in fish meat can provoke allergic responses, information on distribution of parasites and their variability is essential for the implementation of food safety practices.

A new species of Hedruris Nitzsch, 1821 (Nematoda: Hedruridae) parasitic in the freshwater fish Oligosarcus jenynsii (Günther, 1864) (Characidae) from Argentina.

Nematodes belonging to genus Hedruris Nitzsch, 1821 (Nematoda: Hedruridae) were found in the stomach of the freshwater fish Oligosarcus jenynsii (Günther, 1864) (Characidae) from a shallow eutrophic lake in Argentina. Morphological comparisons with congeneric relatives showed that these nematodes belong to a new species, for which H. bifida n. sp. is proposed. Hedruris bifida n. sp. can be distinguished from its congeners by the following combination of characters: bifid deirids, absence of precloacal papillae and nine pairs of postcloacal papillae and non-mammillated eggs. The new species closely resembles Hedruris suttonae Brugni & Viozzi, 2010¸ the only known species from Argentina; however, the bifid deirids in the new species and the distribution pattern of perianal spines in females clearly distinguish both species. Hedruris bifida n. sp. represents the second nominal species of the genus in Argentina and the eighth species described in the Neotropical region.

Dactylogyrid monogeneans parasitising Cyphocharax voga (Hensel) (Teleostei: Curimatidae) from the Pampas region, Argentina: new and previously described species.

Most studies on dactylogyrid monogeneans in Argentina have been carried out during 1980s and 1990s. Many of these species have been later synonymised and other remain under a confusing taxonomic status, particularly those parasitising Cyphocharax voga (Hensel) (Teleostei: Curimatidae). In order to clarify the identity of dactylogyrids, new material was collected from fishes in Lake Chascomús, Buenos Aires Province, Argentina. A total of four species was found in the gills of C. voga. Two known species, Curvianchoratus singularis (Suriano, 1980) Suriano, 1986 and Palombitrema triangulum (Suriano, 1981) Suriano, 1997, are redescribed and their generic and specific status discussed, and two new species are described. Urocleidoides surianoae n. sp. can be distinguished from its congeners by having an anterior medial projection in the ventral bar and a laminar ligament connecting the base of the male copulatory organ and accessory piece. Annulotrematoides bonaerensis n. sp. differs from its congeners principally by having a ventral bar with an anterior medial projection. The diversity of dactylogyrids harboured by C. voga indicates the need of further studies in the Pampas region, which will provide interesting and valuable sources of evidence for future zoogeographical and evolutionary research on dactylogyrids in the Neotropics.

Characithecium (Monogenoidea: Dactylogyridae) parasitic on the Neotropical fish Oligosarcus jenynsii (Teleostei: Characidae) from the Pampasic region, Argentina, with the emendation of the genus.

Presently, only 2 species of dactylogyrid monogeneans have been reported Characidae inhabiting lakes and streams from the Pampasic region (central Argentina). During a parasitological survey on the characid Oligosarcus jenynsii, from Nahuel Rucá Lake (Buenos Aires province, Argentina), dactylogyrids were found on the gills. Specimens were identified as members of Characithecium: C. chascomusensis n. comb, C. longianchoratum n. sp., C. robustum n. sp., C. quadratum n. sp. and C. chelatum n. sp. These species can be distinguished from each other mainly by differences in the shape of the accessory piece of the male copulatory organ, morphology of anchors and ventral bars as well as position of vaginal aperture. The observation of some additional features present in all species studied, such as the vaginal aperture position (as midventral, lateroventral or lateromarginal) and the variability in the morphology of ventral bar (posteromedial projection present or absent) justified an emended diagnosis of Characithecium. 

Pseudascarophis brasiliensis sp. nov. (Nematoda: Cystidicolidae) parasitic in the Bermuda chub Kyphosus sectatrix (Perciformes: Kyphosidae) from southeastern Brazil.

A new species of Pseudascarophis (Nematoda: Cystidicolidae) found in the stomach of Kyphosus sectatrix (Linnaeus) (Kyphosidae), off Rio de Janeiro, Brazil, is described. The new species can be differentiated from the other congeners by the presence of lateral alae, distinct but inconspicuous cephalic papillae at the anterior end, three pairs of precloacal and one pair of adcloacal papillae in males, egg morphology and morphometry of glandular oesophagus and spicules. Pseudascarophis tropica is transferred to Ascarophis as Ascarophis tropica (Solov'eva) comb. n. due to its ambiguous diagnosis.

Pseudascarophis brasiliensis sp. nov. (Nematoda: Cystidicolidae) parasitic in the Bermuda chub Kyphosus sectatrix (Perciformes: Kyphosidae) from southeastern Brazil

A new species of Pseudascarophis (Nematoda: Cystidicolidae) found in the stomach of Kyphosus sectatrix (Linnaeus) (Kyphosidae), off Rio de Janeiro, Brazil, is described. The new species can be differentiated from the other congeners by the presence of lateral alae, distinct but inconspicuous cephalic papillae at the anterior end, three pairs of precloacal and one pair of adcloacal papillae in males, egg morphology and morphometry of glandular oesophagus and spicules. Pseudascarophis tropica is transferred to Ascarophis as Ascarophis tropica (Solov'eva) comb. n. due to its ambiguous diagnosis.

A new species of Caudotestis (Digenea: Opecoelidae) parasitizing the horsefish, Congiopodus peruvianus (Scorpaeniformes: Congiopodidae) from the Patagonian Shelf, Argentina.

A new species of digenean, Caudotestis patagonensis n. sp. (Digenea: Opecoelidae), is described and illustrated based on specimens collected from the intestine of the horsefish, Congiopodus peruvianus (Cuvier, 1829) (Scorpaeniformes: Congiopodidae) from the Patagonian Shelf, Argentina (45-48 ° S, 60-64°W). This opecelid differs from the 4 previously known species of Caudotestis mainly in the extent of its seminal vesicle within the hindbody and the distribution of vitelline follicles. Moreover, the new species can also be distinguished by possessing the following combination of features: oral and ventral suckers nearly equal in size, ventral sucker at boundary of anterior third of body, intestinal bifurcation in posterior third of forebody and anterior to genital pore, genital pore submedial sinistral, anteriormost extent of the excretory vesicle reaching ovarian region, ovary nearly equidistant from both ventral sucker and anterior testis, posteriormost extent of the uterine loops just reaching ovarian region, testes oval and in tandem, ceca ending in front of the anterior testis, and size and number of eggs. This is the fifth recognized species of Caudotestis, the first report of a species of this genus in the southern Atlantic Ocean, and the second from a congiopodid fish.

A new species of Acanthochondria (Copepoda: Chondracanthidae) parasitizing the flounder Xystreurys rasile (Pleuronectiformes: Paralichthyidae) from Argentina.

A new copepod species, Acanthochondria sagitta sp. n., is described based on specimens collected from the flounder Xystreurys rasile (Jordan) (Pleuronectiformes, Paralichthyidae), caught in the coastal waters off Necochea, Buenos Aires Province, Argentina. The new species differs from its congeners by the following combination of characters: presence of three pairs of cephalic outgrowths; the triangular shape of the trunk with diverging postero-lateral processes; leg 2 of an intermediate shape between Types C and D, which projects laterally from the trunk, and Type B-V antennule bearing two proximal processes (one ventral and one dorsal) on the swollen basal portion.

New species of Acanthochondria (Copepoda: Chondracanthidae) infecting the longtail southern cod, Patagonotothen ramsayi (Perciformes: Nototheniidae), from Patagonian waters, Argentina.

Acanthochondria lilianae n. sp. (Copepoda: Chondracanthidae) is described and illustrated based on specimens of both sexes collected from inner surface of the operculum of the longtail southern cod, Patagonotothen ramsayi (Regan) (Perciformes: Nototheniidae), from the Patagonian Shelf, Argentina (42-48°S, 60-63°W). Acanthochondria lilianae n. sp. is characterized by the combination of a Type B-III antennule and Type A leg 2, in addition to both the cephalosome and the trunk being wider than long. The new species most closely resembles Acanthochondria incisa Shiino, 1955, Acanthochondria ophidii (Krøyer, 1863), Acanthochondria priacanthi Shiino, 1964, and Acanthochondria tasmaniae Heegaard, 1962, but differs from these species in the general measurements and proportions of the body, shape and size of head, shape and size of genitoabdomen, and fine details of appendages such as the armature of antennule, ornamentation of both pairs of legs, number of teeth on mandible and maxilla, and ornamentation on maxilliped. This is the first Acanthochondria species recorded from a nototheniid and the second southernmost record of a species of this genus in the southwestern Atlantic Ocean.

Parasites of a marine benthic fish in the Southwestern Atlantic: searching for geographical recurrent patterns of community structure.

Parasite communities of Raneya brasiliensis are described and its parasites used as biological tags to discriminate its populations. Fish were caught in two zones of the Argentine Sea: one sample from San Jorge Gulf (Patagonian Region) and three samples from off the coast of Buenos Aires (Bonaerense Region). A total of 183 fish were examined for parasites and 11 species were found. Host body size and its ecology are pointed out as drivers of the paucity of taxa found. Multivariate similarity analyses allowed the identification of three stocks: one in the San Jorge Gulf, and two other in the Bonaerense Region. The parasite species that contributed most to the separation of the samples were generally those identified as biological markers in previous studies in the area. Patterns of distance decay in similarity among communities in R. brasiliensis were found; with dissimilarity values between distant localities being higher than between close ones. Whereas the composition and structure of parasite assemblages in Bonaerense waters reflect those of other fish species in this region, being mainly determined by the composition of the compound community, no repeatable patterns were found in the composition of parasites assemblages when R. brasiliensis was compared with other hosts species in Patagonia.

Parasite assemblages of Nemadactylus bergi (Pisces: Latridae): the role of larval stages in the short-scale predictability.

The short-scale temporal repeatability in the structure and composition of parasite communities of Nemadactylus bergi were analyzed by comparing population and infracommunity descriptors in five samples caught off Mar del Plata, Argentina (38º 27' S, 57º 90' W) at intervals of 20 days. This is the first study aiming to detect relevant local or short-term processes in an area where larval endohelminths dominate the parasite assemblages and are expected to provide predictability to the communities they belong. The parasite fauna of this host species was composed by 18 species, 16 of them being endoparasites, among which larval stages accounted for most of both the number of parasite individuals found and the highest percentages of average similarity among infracommunities. The structure of parasite communities of N. bergi was, as predicted, repeatable across samples at short spatial and temporal scales and, as expected, this predictability was mainly provided by larval stages, namely Corynosoma australe and Grillotia carvajalregorum. These results imply that a single sample of N. bergi from this locality will be enough to catch the structure and intrinsic variability of their component communities in further studies aiming to compare parasite assemblages at larger spatial scales. These studies should, however, take into account the heterogeneity in the size of fish among samples, which proved to be an important confounding factor in comparisons among samples by affecting their similarity.

Redescription of Gessyella latridopsis (Johnston et Mawson, 1945) (Nematoda: Capillariidae), a parasite of latrid fishes from the southern hemisphere.

The type species of the monotypic genus Gessyella Freitas, 1959, G. latridopsis (Johnston et Mawson, 1945) (Nematoda: Capillariidae), is redescribed from specimens found in the rectum of the marine fish Nemadactylus bergi Norman (Latridae, Perciformes) (a new host record) from the southwestern Atlantic Ocean off Mar del Plata, Argentina. In addition to the morphological and biometrical variability of this species, some new, previously unreported taxonomic features, such as the extent of the spination of the spicular sheath, the morphology of the spicular canal, the distal end of the spicule, the ejaculatory duct, the cloaca, the seminal vesicle, vas deferens and the testis, are described for the first time. Despite the long geographical distance of G. latridopsis records (Australia vs. Argentina), the morphology of the newly collected specimens is in agreement with the existing descriptions of G. latridopsis and both host species are closely related. Therefore, the Argentine specimens are considered to belong to this species.

A new species of Paracapillaroides (Nematoda: Capillariidae) parasitizing Nemadactylus bergi (Perciformes: Latridae) from the Argentine Sea.

A new nematode species, Paracapillaroides acanthocotylus sp. n., is described from the marine fish Nemadactylus bergi (Norman) (Latridae, Perciformes) from waters off Mar del Plata, Argentina (38 degrees 08'S, 57 degrees 32'W) (prevalence 81.8%, mean intensity 12.4 +/- 10.3). The new species is readily distinguished from P. agonostomi Moravec, Salgado-Maldonado et Caspeta-Mandujano, 1999, the only known species of the genus, by having in both sexes a longer oesophagus in relation to total body length. Males of the new species have a shorter and more complex spicule and a markedly different morphology of the spicular sheath; the rays supporting the caudal bursa are also shorter and rounded, instead of digitiform. Furthermore, females of the new species have elevated vulval lips and longer eggs. The complex structure of both the spicule and spicular sheath is unique among all capillariids parasitizing cold-blooded vertebrates. This is the first record of a species of Paracapillaroides in the southwestern Atlantic Ocean.

The importance of the compound community on the parasite infracommunity structure in a small benthic fish.

The extent to which the structure of parasite infracommunities and component communities is determined by the composition of the compound community was assessed by determining the importance of unspecific larval parasites relative to the other guilds (ectoparasites and adult endoparasites). This was analyzed under the hypothesis that the infracommunities harbored by any fish species in coastal waters of the northern Argentine sea will be dominated by unspecific larval stages, which also will be the determinants of the infracommunity structure. These predictions were tested in the Atlantic sea robin, Prionotus nudigula. A total of 1,570 metazoans belonging to 11 species were found in the overall sample (total prevalence = 98%). Larval endoparasites, especially Corynosoma australe and Grillotia sp., were the best represented species, with a deep influence on the infracommunity structure, accounting for the highest proportion of individuals, dominating about 60% of the infracommunities, greatly determining all infracommunity descriptors, and producing marked changes in the similarity among infracommunities. Given the abundance and broad distribution of unspecific larval parasites in the compound community, infracommunities can be considered as subsets of the species available regionally. They are obtained by passive sampling of infective stages as fish feed, and lead to predictable assemblages, with a non-random composition and structure modeled mainly by ecological filters.

Causes of inter-individual variation in reproductive strategies of the parasitic nematode Graphidioides subterraneus.

Several factors capable of affecting the amount of resources available to an individual parasite, such as the number of other parasites in the host or host quality, may cause variability in reproductive success among parasites. Variation in egg output and mean egg volume was investigated among adult females of the nematode Graphidioides subterraneus, parasitic in the herbivorous subterranean rodent Ctenomys talarum (Octodontidae). Female nematode body size correlated strongly with the number of eggs produced. However, neither host body mass nor the number of other nematodes per host had any influence on the number or volume of eggs produced by the parasites. There was also no evidence for a trade-off between the number of eggs produced and mean egg volume among female nematodes. All these results suggest that resource supply to individual worms is not limited by host size or by the number of conspecific parasites vying for the same resources, despite the 30-fold variation in intensity of infection and the twofold variation in host body mass observed in the present study. Instead, resource availability does not appear to constrain reproduction in G. subterraneus, with its host providing a stable, predictable environment.

Is there a trade-off between fecundity and egg volume in the parasitic copepod Lernanthropus cynoscicola?

Negative relationships between egg number and egg size are commonly seen in many animal taxa, supporting the idea that there is a trade-off between egg number and egg size resulting from the allocation of resources to either one or the other. In parasites, where availability of resources is presumably very high, there may be fewer energetic constraints acting on allocation strategies, and the trade-off may be weakened. We investigated the association between egg number and egg volume among females of the copepod Lernanthropus cynoscicola Timi and Etchegoin, 1996, parasitic on the fish Cynoscion guatucupa (Cuvier). Both egg number and egg volume were strongly correlated with female body size. After controlling for the effects of body size, we found absolutely no evidence of a trade-off, i.e. no negative relationship, between egg number and egg volume. For a given body length, females that produce many eggs do not tend to produce relatively small eggs, and vice versa. In contrast, under conditions in which resources are plentiful, large females produce large quantities of high-quality eggs, and have a marked fitness advantage over small females.