Distribution patterns of two species of Corynosoma (Acanthocephala: Polymorphidae) in fishes from Southwestern Atlantic.

Corynosoma australe and C. cetaceum are the most frequently reported acanthocephalans in fish from the Argentine Sea, particularly in central and northern areas. Their definitive hosts are otariids and odontocete cetaceans, respectively. The low specificity of these larvae, in combination with high infective capability and long survival periods in fish, make them potentially good biological markers for stocks and other biological features of their fish hosts. In order to determine the distribution patterns of these species and their determining factors, a large dataset composed by newly collected fish samples, published and unpublished data from previous studies by the authors in the region were analysed in relation to host and environmental variables. The complete dataset comprised a total of 5084 fish, belonging to 29 species distributed in 21 families and 9 orders. Host size and trophic habits arose as the main determinants of abundance for both species of Corynosoma, showing higher abundances on larger fish and on higher trophic levels, as it is usual for trophically transmitted parasites. Biogeographic province and depth (indirectly representing the temperature of water) were the main drivers of the spatial distribution, displaying a latitudinal pattern associated to the temperature clines created by the interaction of Malvinas and Brazil currents, determining a decrease in abundance southwards and towards the deeper areas. No patterns were found regarding the distribution of definitive hosts. The knowledge of these distribution patterns of Corynosoma spp. in fish at regional scale, as well as of their causes, provides useful information to design management and conservation policies thus contributing to maintain the full and sustainable productivity of fisheries.

Merizocotyle euzeti sp. n. (Monogenea: Monocotylidae) from the nasal tissue of three deep sea skates (Rajidae) in the southwestern Atlantic Ocean.

A new species of Merizocotyle Cerfontaine, 1894 (Monogenea: Monocotylidae) is described from the nasal tissues of three deep sea rajid skates: the southern thorny skate, Amblyraja doellojuradoi (Pozzi), broadnose skate, Bathyraja brachyurops (Fowler), and yellownose skate, Zearaja chilensis (Guichenot), collected off Buenos Aires Province, Argentina, southwest Atlantic Ocean. Two additional species of sympatric rajid, the white-dotted skate, Bathyraja albomaculata (Norman), and the Patagonian skate, Bathyraja macloviana (Norman), were also examined but no merizocotylines were found. The taxonomy of the Merizocotylinae is not widely accepted and, as a result, the status of Thaumatocotyle and Mycteronastes, and their proposed synonymy with Merizocotyle are currently under discussion. The new species differs from its congeners by having a unique haptoral structure, 6 peripheral loculi that are asymmetrically arranged (one much smaller, indistinctly located in the left or right side of the haptor). The presence of the new species in three sympatric species of Rajidae belonging to distinct genera and subfamilies, as well as its absence in sympatric congenerics indicates the lack of phylogenetic host specificity. Host ecology and geographical distribution appear to be more important than host phylogeny in determining the distribution of this parasite across potential hosts in the region. This constitutes the first record of Merizocotyle in the southwestern Atlantic Ocean.

Plerocercoids of Adenocephalus pacificus in Argentine hakes: Broad distribution, low zoonotic risk.

Adenocephalus pacificus is a tapeworm parasitic of marine mammals and the main agent of human diphylobothriosis caused by consumption of raw or undercooked marine fishes, being considered as a reemerging disease. Despite having a broad distribution in marine mammals in both hemispheres, plerocercoid larvae in fish have only been reported in the Pacific Ocean, in Peruvian waters, from where most human cases are known. In Argentine waters larval stages of Diphyllobothriidae have been recorded in Merluccius hubbsi, a main fish resource mostly exported frozen, headed and gutted (H&G) or as fillets; therefore, the possible presence of A. pacificus in edible products, and the extent of the risk of parasitism for humans becomes of health and commercial relevance. With the aim of detecting and identifying potentially zoonotic diphyllobothriids and quantifying infection levels in viscera and fillets of hakes, 43 entire fish, 471 H&G, and 942 fillets obtained from research cruises in 2019 and 2021 from the southern Argentine Sea (44-53°S; 63-68°W) were examined by transillumination and under stereoscopic microscopy. Plerocercoids were recovered at low prevalence and mean abundance in entire fish (13.95 % and 0.35) and H&G fish (2.76 % and 0.03) but no larval worms were found adhered to musculature or peritoneum, furthermore, no larvae were found in the fillets. Larvae were genetically identified, based on sequences of the large subunit ribosomal RNA nuclear gene (lsrDNA) and the cytochrome c oxidase subunit 1 (cox1) mitochondrial gene, as members of A. pacificus, representing the first report of this species in a fish host outside South American Pacific coasts. No spatial nor bathymetric patterns in parasite burdens were observed across sampling sites, but prevalence increased with fish size. The recorded low parasite burdens, the absence of infective stages in fillets and the fact that most products are commercialized deeply frozen, diminish the risk of parasitism for consumers to a minimum. However, the identification of this zoonotic agent and the assessment of its distribution in fish products are a first indispensable step for the design of efficient and suitable measures, such as freezing or cooking meet, to ensure the prevention of human infections.

Correlated evolution of fish host length and parasite spore size: a tale from myxosporeans inhabiting elasmobranchs.

Myxozoa represent a diverse group of microscopic cnidarian endoparasites alternating between invertebrate and vertebrate hosts. Of the approximately 2,600 species described predominantly from teleost fish, only 1.8% have been reported from cartilaginous fishes (Elasmobranchii). As ancestral vertebrate hosts of myxozoans, elasmobranchs may have played an important role in myxozoan evolution, however, they are also some of the largest vertebrate hosts known for this group of parasites. We screened 50 elasmobranchs belonging to nine species and seven families, from various geographical areas, for myxozoan infection. We found a 22% overall prevalence of myxozoans in elasmobranchs and describe five species new to science. We investigated, for the first known time, the evolution of spore size within three phylogenetic clades, Ceratomyxa, Sphaerospora sensu stricto and Parvicapsula. We found that spores from elasmobranch-infecting myxozoans were on average 4.8× (Ceratomyxa), 2.2× (Parvicapsula clade) and 1.8× (Sphaerospora sensu stricto except polysporoplasmic Sphaerospora spp.) larger than those from teleosts. In all analysed clades, spore size was correlated with phylogenetic position. In ceratomyxids, it was further strongly positively correlated with fish body size and habitat depth, independent of cellular composition of the spores and phylogenetic position in the tree. While in macroparasites a host size-correlated increase in parasite size occurs on a large scale and is often related to improved exploitation of host resources, in microscopic parasites size ranges vary at the scale of a few micrometres, disproportionate to the available additional space in a large host. We discuss the ecological role of these changes with regard to transmission under high pressure and an invertebrate fauna that is adapted to deeper marine habitats.

Pauciconfibula patagonensis sp. nov. (Monogenea: Microcotylidae) parasitizing the horsefish, Congiopodus peruvianus (Pisces: Congiopodidae), from the Patagonian Shelf, Argentina.

Pauciconfibula patagonensis sp. nov. (Monogenea: Microcotylidae), parasite of gill filaments of the horsefish, Congiopodus peruvianus (Congiopodidae) collected in the Patagonian Shelf, Argentina, is described and illustrated. The new species is characterized by having intestinal caeca not confluent and entering into the haptor, vitelline follicles extending from the genital pore to near the posterior portion of haptor, two parallel rows each comprised of 16-20 microcotylid clamps in the haptor, 25-43 testes and a fusiform egg with one very long tangled polar filament. P. patagonensis is the only member of the genus known to parasitize a scorpaeniform host and represents the first record of a representative of this genus in the southern Atlantic Ocean.

Males of Ichthyofilaria argentinensis Incorvaia, 1999 and I. bergensis (Wülker, 1930) (Dracunculoidea:Guyanemidae): new morphological aspects and emendation of the generic diagnosis.

Abstract: The adult male of dracunculoid nematode Ichthyofilaria argentinensis Incorvaia, 1999 (Guyanemidae) is described for the first time based on specimens found in the swimbladder of its type host, Merluccius hubbsi Marini (Merlucciidae), caught off the coast of Buenos Aires, Argentina (western Atlantic Ocean). In addition, the males of Ichthyofilaria bergensis (Wülker, 1930) Køie, 1993 are redescribed from specimens collected from the body cavity and visceral surface of Molva macrophthalma (Rafinesque) (Lotidae) caught in the western Mediterranean Sea, off the coast of Sardinia. Light and scanning electron microscopy examinations revealed some new morphological features for the genus, such as a pair of deirids located near the end of muscular oesophagus, the body wall conspicuously twisted immediately anterior to the cloaca, the presence of a copulatory plate, one pair of adcloacal papillae and a pair of phasmids situated on the posterior half of the tail. On the basis of this material, the generic diagnosis of Ichthyofilaria is modified to include some of these newly observed features, as well as to indicate the absence of spicules. The diagnosis of Guyanemidae is extended to include that a copulatory plate and/or two spicules may be present as characteristics for this family.

A new species of Capillostrongyloides (Nematoda: Capillariidae) parasitizing the horsefish, Congiopodus peruvianus (Pisces: Congiopodidae), from Argentina.

A new species of parasitic nematode, Capillostrongyloides congiopodi n. sp. (Capillariidae), is described based on specimens collected from the gall bladder of the horsefish, Congiopodus peruvianus Cuvier and Velenciennes (Congiopodidae, Scorpaeniformes), from the Patagonian Shelf, Argentina (45-48 degrees S; 60-64 degrees W). Among the 9 species described so far in the genus, the new species most closely resembles C. norvegica Moravec and Karlsbakk, 2000, by the presence of its conspicuously elevated anterior vulvar lip in females; however, it is readily distinguished from it by having a larger body size, larger eggs with protruding polar plugs, the shape and length of the spicule, and mainly by the general morphology of the caudal bursa of males. In addition, the site of infection, i.e., stomach versus gall bladder. This is the first Capillostrongyloides species reported from fishes in the southern Atlantic Ocean.

Influence of confluent marine currents in an ecotonal region of the South-West Atlantic on the distribution of larval anisakids (Nematoda: Anisakidae).

BACKGROUND: In the marine environment, transitional zones between major water masses harbour high biodiversity, mostly due to their productivity and by containing representatives of species characteristic of adjacent communities. With the aim of assessing the value of larval Anisakis as zoogeographical indicators in a transitional zone between subtropical and sub-Antarctic marine currents, larvae obtained from Zenopsis conchifer were genetically identified. Larvae from Pagrus pagrus and Merluccius hubbsi from two adjacent zoogeographical provinces were also sequenced. RESULTS: Four species were genetically identified in the whole sample, including Anisakis typica, A. pegreffii, A. berlandi and a probably new species related to A. paggiae. Anisakis typica and A. pegreffii were identified as indicators of tropical/subtropical and sub-Antarctic waters, respectively, and their presence evidenced the transitional conditions of the region. Multivariate analyses on prevalence and mean abundance of Anisakis spp. of 18 samples represented by 9 fish species caught south of 35°S determined that host trophic level and locality of capture were the main drivers of the distribution of parasites across zoogeographical units in the South-West Atlantic. CONCLUSIONS: Most samples followed a clear zoogeographical pattern, but the sample of Z. conchifer, composed mostly of A. typica, was an exception. This finding suggests that population parameters of A. typica and A. pegreffii could differ enough to be considered as a surrogates of the identity of larvae parasitizing a given host population and, therefore, a step forward the validation of the use of larval Anisakis as biological indicators for studies on host zoogeography.

Parasitic copepods infesting the olfactory sacs of skates from the southwestern Atlantic with the description of a new species of Kroeyerina Wilson, 1932.

The olfactory sacs of 488 specimens belonging to 18 species of rajid and arhynchobatid skates from the Argentine Sea were sampled for parasites. No parasitic copepods were found in 11 host species, but siphonostomatoid specimens referable to Kroeyerina Wilson, 1932 (Kroyeriidae) and Brianella corniger Wilson, 1915 (Lernaeopodidae) were found on the spotback skate Atlantoraja castelnaui (Miranda Ribeiro, 1907), the smallnose fanskate Sympterygia bonapartii Müller & Henle, 1841, the bignose fanskate Sympterygia acuta Garman, 1877 and the zipper sand skate Psammobatis extenta (Garman, 1913) (Rajiformes: Arhynchobatidae). Additionally, specimens of B. corniger were found in the olfactory sacs of the Rio skate Rioraja agassizii (Müller & Henle, 1841) and attached to the pectoral fins of the Magellan skate Bathyraja magellanica (Philippi, 1902) and the smallthorn sand skate Psammobatis rudis Günther, 1870. A new species, Kroeyerina sudamericana sp. nov., is described and illustrated. The new species most closely resembles Kroeyerina nasuta Wilson, 1932, but can be distinguished from it by the different armature of the antennule, a proportionally shorter genital complex and the chela of the antenna which, when closed, leaves a gap between the corpus and claw, the latter having no spines. The new species represents the first record of Kroeyerina in South American marine waters. The present study also extends the distribution range of B. corniger, previously known only from the Pacific, to include Atlantic waters, and records seven new host species, all of which are members of the Arhynchobatidae.

Ecotonal marine regions - ecotonal parasite communities: helminth assemblages in the convergence of masses of water in the southwestern Atlantic Ocean.

With the aim of evaluating the utility of marine parasites as indicators of ecotonal regions in the marine environment, we analysed data on assemblages of long-lived larval parasites of Zenopsis conchifer inhabiting the region of convergence of three masses of water in the southwestern Atlantic Oceans. These masses of water with different origins are expected to affect the structure of parasite communities by acting as sources of infective stages of helminth species typical of adjacent zoogeographical regions. Multivariate analyses at both infracommunity and component community levels, including data of four other species recognised as harbouring parasite assemblages representatives of these zoogeographical regions, were carried out to corroborate the existence of repeatable distribution patterns and to provide further evidence of the utility of parasites as zoogeographic indicators in the region. Results showed a tight correspondence with the existing zoogeographical classification in the study region, namely two zoogeographical provinces, one of which is subdivided into two districts demonstrating the ecotonal nature of parasite assemblages from the convergence region, which were characterised by a species rich component community but depauperate and heterogeneous infracommunities. The borders of biological communities have been suggested as priority areas for conservation where a fully functioning ecosystem can be protected and parasite communities can be considered as reliable indicators to define such transitional regions.