Parasite assemblages of whitemouth croaker, Micropogonias furnieri: comparison between marine and brackish waters from the Argentine Sea.

The whitemouth croaker, Micropogonias furnieri, a coastal demersal fish with wide distribution in the Southwest Atlantic Ocean, is a euryhaline species, inhabiting waters with a wide range in salinity. Here, the composition of parasite assemblages of M. furnieri caught along the coastal area off Mar del Plata, Argentina, was described and the infracommunity structure compared with fish from brackish waters to determine variations of its parasite communities due to fish migration between these environments. The relationships between the presence of parasites and the diet and ecological traits of this fish host were discussed. A total of 61 fish from Mar del Plata (MDP) were examined for parasites and compared with previously published data for whitemouth croakers from Mar Chiquita coastal lagoon (MCH), an estuarine system connected to the sea. Corynosoma australe, Dichelyne sciaenidicola, and Neopterinotrematoides avaginata were the most prevalent and abundant species in MDP. Comparisons of infracommunity descriptors showed that fish from MDP harbored a higher number of parasites, as well as richer and more diverse infracommunities than those of MCH. Significant differences occurred in the structure and composition of parasite assemblages of whitemouth croaker from MDP compared to those from MCH, in which Neomacrovalvitrema argentinensis, N. avaginata, Neobrachiella chevreuxii, D. sciaenidicola, and C. australe were the key discriminating species related to these differences. The present study provides comparative data, of great importance for the understanding of parasite-host-environment interactions, particularly in a host that alternates between brackish and marine waters during its life cycle.

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.

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.

Molecular identification, morphological characterization and new insights into the ecology of larval Pseudoterranova cattani in fishes from the Argentine coast with its differentiation from the Antarctic species, P. decipiens sp. E (Nematoda: Anisakidae).

Larvae of the genus Pseudoterranova constitute a risk for human health when ingested through raw or undercooked fish. They can provoke pseudoterranovosis in humans, a fish-borne zoonotic disease whose pathogenicity varies with the species involved, making their correct specific identification a necessary step in the knowledge of this zoonosis. Larvae of Pseudoterranova decipiens s.l. have been reported in several fish species from off the Argentine coasts; however, there are no studies dealing with their specific identification in this region. Here, a genetic identification and morphological characterization of larval Pseudoterranova spp. from three fish species sampled from Argentine waters and from Notothenia coriiceps from Antarctic waters was carried out. Larvae were sequenced for their genetic/molecular identification, including the mitochondrial cytochrome c oxidase subunit II (mtDNA cox2), the first (ITS-1) and the second (ITS-2) internal transcribed spacers of the nuclear ribosomal DNA, and compared with all species of the P. decipiens (sensu lato) species complex (sequences available in GenBank). Further, adults of Pseudoterranova spp. from the definitive host, the southern sea lion, Otaria flavescens, from Argentine and Chilean coasts were sequenced at the same genes. The sequences obtained at the ITS-1 and ITS-2 genes from all the larvae examined from fish of Argentine waters, as well as the adult worms, matched 100% the sequences for the species P. cattani. The sequences obtained at mtDNA cox2 gene for Antarctic larvae matched 99% those available in GenBank for the sibling P. decipiens sp. E. Both MP and BI phylogenetic trees strongly supported P. cattani and P. decipiens sp. E as two distinct phylogenetic lineages and depicted the species P. decipiens sp. E as sister taxon to the remaining taxa of the P. decipiens complex. Larval morphometry was similar between specimens of P. cattani from Argentina, but significantly different from those of P. decipiens sp. E, indicating that larval forms can be distinguished based on their morphology. Pseudoterranova cattani is common and abundant in a variety of fish species from Chile, whereas few host species harbour these larvae in Argentina where they show low levels of parasitism. This pattern could arise from a combination of factors, including environmental conditions, density and dietary preferences of definitive hosts and life-cycle pathways of the parasite. Finally, this study revealed that the life-cycle of P. cattani involves mainly demersal and benthic organisms, with a marked preference by large-sized benthophagous fish.

Parasite communities in three sympatric flounder species (Pleuronectiformes: Paralichthyidae): similar ecological filters driving toward repeatable assemblages.

The relative role of host phylogeny and ecology on parasite community structure is analyzed in three sympatric paralichthyids from Argentine waters: the carcinophagous Xystreurys rasile and the piscivorous Paralichthys isosceles and P. patagonicus. Their relatedness, inherited ecological and physiological traits and shared past histories should result in certain similarities in their parasite assemblages. With this as our null hypothesis, we focused on the effects of measurable traits (size, age and diet) across fish species, with departures from a general pattern being interpreted as a consequence of ecological filters preventing homogeneous infections. The percentage of individuals/species that host-specific parasites contributed to each component community, as well as their effect on similarity of assemblages within/across host species, showed that they were not important contributors to abundance, richness and similarity, being irrelevant for the repeatability within component communities and across fish species as a phylogenetically related group. To minimize the effect of variables other than diet or trophic level only trophically transmitted nonspecific parasites were included in further analyses. After controlling for fish size, the congeneric host species harboured assemblages significantly different from those found in X. rasile, but were similar to each other because of their shared high trophic levels. Assemblages of equivalent structure harboured by fish with different age-size relationships showed that these variables seem to act at dissimilar rates on different features of the parasites assemblages. Indeed, age affected mainly the parasite abundance, whereas body size influenced mostly species richness. In conclusion, similar ecological filters produce analogous infections across host species driving towards homogeneous parasite communities.

A new species of Dichelyne (Nematoda: Cucullanidae) parasitizing Pogonias cromis (Pisces: Sciaenidae) from Mar Chiquita coastal lagoon, Argentina.

A new nematode species Dichelyne (Cucullanellus) mariajuliae n. sp., is described based on specimens collected from the black drum, Pogonias cromis (Linnaeus, 1766), from Mar Chiquita coastal lagoon, Buenos Aires Province, Argentina (37 degrees 32'S, 57 degrees 19'W) (prevalence 75%, mean intensity 3.75). Among Dichelyne (Cucullanellus), the new species is unique in having the papillae 2 situated at the level of ventral sucker in males and bearing subcuticular ornamentation in the female tail.