Carmen Gilardoni

During a parasitological survey of freshwater fishes from Khun Thale Swamp, Surat Thani Province, Thailand, a new species of opecoelid trematode, Dactylostomum brayi n. sp., was recovered from the intestine of the Asian redtail catfish Hemibagrus nemurus (Bagridae). Of the 1065 fishes examined, representing 33 species, 27 genera, and 16 families, the parasite was found exclusively in H. nemurus, with a prevalence of 27.27% and a mean intensity of 2.33 worms per infected host, suggesting a high degree of host specificity. The new species differs from all recognised freshwater congeners in the number of ventral sucker papillae, body proportions relative to the oral sucker, and the morphology of the reproductive organs. This represents the second record of Dactylostomum from Thailand, following specimens identified as Dactylostomum sp. by R. A. Bray from the same host and deposited in the Natural History Museum, London, in 1983. The present study also provides the first molecular characterisation (18S, ITS2, and 28S rRNA) for the genus Dactylostomum and reveals a close phylogenetic relationship with Dimerosaccus. These findings contribute to the taxonomy and distribution of Dactylostomum and provide a basis for future systematic and phylogenetic studies of this poorly known genus.

A new species of Prodistomum (Digenea, Lepocreadiidae), Prodistomum chumphonense sp. nov ., is described from the intestine of Rastrelliger kanagurta and Rastrelliger brachysoma (Scombridae) collected in the Gulf of Thailand. The new species is characterized by vitelline follicles confined to the hindbody but extending anteriorly to the level of the anterior to posterior margin of the ventral sucker; a ventral sucker consistently larger than the oral sucker; an esophageal region approximately equal in length to the prepharynx; an entire, oval ovary; and a tubular excretory vesicle terminating below the level of the intestinal bifurcation. The new species differs from most congeners, mainly those with vitelline follicles extending into the forebody, by the restriction of the vitellarium to the hindbody. Although morphometrically similar to some specimens in the literature previously identified as P. orientale , previous molecular phylogenetic analyses based on 18S, ITS2, and 28S rDNA sequences demonstrate that P. chumphonense sp. nov . represents a distinct taxon. The present study underscores the importance of integrating detailed morphometric with molecular data for accurate species delimitation in trematodes of the genus Prodistomum .

The high incidence of anthropogenic impacts in the Mediterranean basin raises concerns on the health and quality of commercial fish species. This study aims to evaluate the health status of the European hake, Merluccius merluccius, from three areas of the Catalan coast (NW Mediterranean Sea) with different anthropogenic impacts (i.e., chemical pollution, litter, …) and assess if hake could serve as a sentinel species. We measured biomarkers of chemical exposure including B-esterases, antioxidant enzymes (GST, GR, GPx, CAT), biotransformation markers (EROD), lipid peroxidation, and macro-parasite assemblages. Hake showed, generally, a good health status across all areas with homogeneous patterns for most parameters. Tissue-specific differences included elevated gonadal cholinesterases and higher brain and hepatic carboxylesterase activities in the south, and increased hepatic EROD but lower lipid peroxidation in the central Barcelona area. Parasite assemblages were dominated by Digenea, Cestoda, and Nematoda, with higher cestode prevalence in both central and south zones. In summary, despite a greater prevalence of environmental pollution in the central region, there was a homogeneous pattern in hake health indicators throughout the three studied fishing zones. These results establish a baseline for hake health in Mediterranean waters and suggest that the species’ high mobility and wide depth range may limit its utility to detect local-scale pollution impacts, though it may serve as a regional-scale bioindicator.

Bivalves serve as the first intermediate hosts in the life cycles of some digeneans, but little is known about their larval stages along the southwestern Atlantic coast. These larvae may provide valuable insights into the ecological role of mollusks in parasite life cycles and marine food webs. This study offers a morphological, histological, and molecular (ITS2, 28S rDNA) description of the larval stages of three digenean species parasitizing the bivalve Jukesena foveolata in the Beagle Channel, Tierra del Fuego Province, Argentina. Sporocysts containing cercariae of a monorchiid species were found infecting the gonads and digestive glands (p = 2%), while metacercariae were encysted in the foot (p = 7%). Additionally, metacercariae of Renicola sp. (Renicolidae) were located between the tubules of the digestive gland (p = 2%), and metacercariae of Bartolius sp. (Gymnophallidae) were found in the extrapallial space (between the mantle and the valve, p = 13.5%), where they elicited a histopathological reaction with the secretion of a calcareous, igloo-shaped coating. The monorchiid larvae are described here for the first time in this bivalve, with fish as their definitive hosts. Metacercariae of Renicola sp. and Bartolius sp., both of which use coastal birds as definitive hosts, have been previously recorded in other mollusks from the Argentine coast. This study contributes to our understanding of the life cycles of digeneans from the southwestern Atlantic coast and the role of bivalve hosts in marine food webs.

Pomacea canaliculata is one of the most dangerous invasive species. Morphological and molecular analyses have revealed that a digenean species belonging to the family Echinostomatidae parasitizes this snail at two sites in Buenos Aires Province, Argentina, South America. Molecular results confirmed that the species belongs to a genus closely related to Patagifer. Analysis of the 28S rDNA showed that the sequences of the rediae and metacercariae are identical, indicating that the apple snail acts as the first and second intermediate host. The cercariae may encyst as metacercaria inside the redia and also emerge and re-infect the same snail or another snail. The prevalence of digeneans was higher in one of the sampling locations (15.1% vs. 0.72%), probably because the bird species that acts as the definitive host is more abundant in that area. Histopathological examination showed that the parasite quickly invades multiple host organs (gills, intestines, albumen gland, lung, kidney, and mantle border) besides the gonad and digestive gland, as is usual in digeneans. In addition, the partial or total castration of snails was observed in cases of moderate and high infection intensity. In males, there was loss of integrity in testicular tubules, while in females, the replacement of ovarian tissue by rediae was found.

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.

The genus Maritrema Nicoll, 1907 (Platyhelminthes, Trematoda, Plagiorchiida, Microphallidae) comprises cosmopolitan species that predominantly parasitize birds. Although approximately 65 species have been described worldwide, including 6 for Argentina, molecular data referring to Maritrema species are still scarce worldwide, especially in South America. Unfortunately, this lack of references for nucleotide sequences is an obstacle to understanding the taxonomy and life cycles of trematodes, and impedes advancing our studies on the phylogeny and geographical distribution of these parasites. For that reason, we performed the molecular study of developmental stages of Maritrema bonaerense: cercariae (collected from the snail first intermediate host Heleobia australis, inhabiting Mar Chiquita lagoon) and metacercariae (collected from the crab second intermediate host Neohelice granulata, inhabiting Mar Chiquita lagoon and San Antonio Oeste, Argentina). The accordance between the ITS2 sequence of M. bonaerense cercaria from the snail H. australis and the sequences of metacercariae from the crab N. granulata was 100%, supporting previous findings of the life cycle of M. bonaerense based on morphological data. All Maritrema species are included in a monophyletic and well-supported clade. Maritrema bonaerense grouped more closely with Maritrema gratiosum. These findings contribute to the knowledge of digeneans in coastal marine ecosystems.

Ecto and endoparasites of four species of coastal birds, Haematopus ater, Larus dominicanus, Leucophaeus scoresbii (Charadriiformes), and Lophonetta specularioides (Anseriformes), are reported from Puerto Deseado on the Patagonian coast, Argentina. Only H. ater was infested with lice (Phthiraptera), belonging to 2 species (Ischnocera, Amblycera). A total of 19 helminth species were found parasitizing the coastal birds studied: 4 cestodes (1 Tetrabothriidae, 3 Cyclophyllidea); 11 trematodes (2 Gymnophallidae, 3 Microphallidae, 2 Notocotylidae, 1 Philophthalmidae, 2 Renicolidae, 1 Schistosomatidae); 3 nematodes (1 Anisakidae, 2 Acuariidae); and 1 acanthocephalan (Polymorphidae). Although some isolated records have been previously reported for these birds, the present work provides a parasitofauna study for H. ater, L. scoresbii, and L. specularioides for the first time. Endoparasites reflected the feeding habits of the birds; the parasite assemblage of L. dominicanus was the richest, indicating their wide prey spectrum and the diversity of the habitats frequented. A great species richness of trematodes, whose life cycles are partially known, suggests that L. specularioides feeds upon crustaceans and small bivalves. The blackish oystercatcher H. ater preys upon the limpet Nacella magellanica which hosts two larval trematodes corresponding to the adults found parasitizing it.