Jorge A. Etchegoin

Parasite assemblages of estuarine-dependent marine fishes from Mar Chiquita coastal lagoon (Buenos Aires Province, Argentina)

The estuarine-dependent marine fish includes marine species that inhabit, at some stage of their life cycle, the Mar Chiquita coastal lagoon, Buenos Aires Province, Argentina. In the present study, we examined for parasites a total of 209 fishes belonging to following the estuarine-dependent marine species: Brevoortia aurea, Odontesthes argentinensis, Mugil platanus, Paralichthys orbignyanus, Micropogonias furnieri, and Pogonias cromis. The parasite fauna in the six host species comprised 43 parasite species, the majority of which represented new locality and new host records. A high percentage of fish was parasitized with at least one parasite species. The greatest values of prevalence were registered for M. furnieri, B. aurea, and P. cromis, at the component community level, followed by P. orbignyanus, O. argentinensis, and M. platanus. On the other hand, B. aurea, O. argentinensis, M. furnieri, and P. cromis showed similar percentages of both larval and adult stages of parasites. In the case of M. platanus, adult stages dominated the total number of parasites, whereas P. orbignyanus harbored mainly larval stages. Out of the six fish species herein studied, M. platanus seems to generally act only as definitive host in the local parasite’s life cycle. From a parasitological point of view, the expression “estuarine-dependent marine fishes” remains valid, although the contribution of the fish species in the lagoon to the maintenance of parasite populations is relatively minor.

Some ecological aspects of the copepod parasites of the common hake, Merluccius hubbsi, from the Argentine-Uruguayan coasts.

A total of 2164 common hake Merluccius hubbsi captured in the Argentine-Uruguayan Common Fishing Zone was examined for parasitic copepods. The fish were infested with Chondracanthus palpifer and Neobrachiella insidiosa f. lageniformis, the former parasitizing the buccal cavity and the latter the branchial arches. C. palpifer showed an increase in both prevalence and intensity in relation to the host size; infestation with N. insidiosa f. lageniformis decreased with increasing length of hake. Attachment site preferences and variations in the parasite distribution patterns as related to the host biology were observed. Evidence of negative association between copepod species and seasonal changes in the parasite composition was also found.

Evaluation of species richness estimators in studies of diversity involving two larval digenean communities parasitizing snail hosts

The nonparametric estimators of species richness are some of the most widely used extrapolation methods in studies of biodiversity. These studies need relative large samples to achieve total diversity (including rare species), and estimators are routinely used to alleviate this problem. In the existing literature, parasite communities have received little attention. In fact, the present study is the first dealing with parasites in invertebrate hosts. Real data on seasonal diversity of larval digeneans in the snails Heleobia conexa and Heleobia australis from Mar Chiquita coastal lagoon (Argentina) were used to evaluate seven nonparametric estimators of species richness, observing the behavior of each method and its ability to estimate the richness using different subsample sizes. In addition, estimated species richness was compared with the previously observed species richness in the parasite component communities of both snail hosts, and the minimum sample size, necessary to include all the observed species of larval digeneans, was estimated using the nonparametric estimators. The bootstrap method had the best overall performance in the two communities. Although this estimator required large subsamples to estimate sample richness, it was in general the least biased and most accurate, and it presented the most similar curve shapes with lack of erratic behavior through the seasons. The results obtained from the comparison between the minimum sample sizes estimated in previous studies of both snail hosts and those suggested by the estimators also support the use of species richness estimators as methods to calculate the minimum sample size in studies of diversity.

Digenetic trematodes of the Brazilian flathead, Percophis brasiliensis Quoy et Gaimard, 1825 (Percophidae, Perciformes), from Argentinean and Uruguayan waters

Based on the examination of 234 specimens of the Brazilian flathead, Percophis brasiliensis (Percophidae), caught in the Argentinean and Uruguayan Seas, the list of digenean species parasitizing P. brasiliensis is increased from 6 to 9, including the specific identification of two species previously reported at the generic level. The three news digenean records for P. brasiliensis are: Elytrophalloides oatesi, Parahemiurus merus and Aponurus laguncula, while that Ectenurus virgulus and Lecithocladium cristatum were identified to specific level. These reports showed the highest diversity of digeneans registered in fishes from the study region. The diversity of the digenean fauna of P. brasiliensis could be a consequence of the generalist food habits of this fish.

Redescription of Bacciger microacetabularis (Martorelli et Suriano, 1983) nov. comb. parasitizing Paralichthys orbignyanus (Pisces, Paralichthyidae) from Argentina

In this paper Steringotrema microacetabularis (Suriano et Martorelli, 1983) is redescribed and transferred to Bacciger Nicoll, 1924 in the Faustulidae Poche, 1926 based on newly collected material from the type-host, Paralichthys orbignyanus Valenciennes, 1839 and the type-locality, Mar Chiquita coastal lagoon, Buenos Aires Province, Argentina. A careful re-examination of the new specimens shows that some anatomical characteristics were ignored or incompletely described by the previous authors and they are included herein. The species is tentatively transferred to Bacciger with which it appears to have closest affinity. Despite the anatomical differences detailed in this paper, confirmation of this proposal must await further work, including molecular studies.

Can the studies at a spatial scale of 100s meters detect the spatiotemporal fluctuations of a parasite assemblage

The importance of small-scale heterogeneity in local factors which overrides that of larger-scales factors, suggest that local factors play a major role in determining the richness and prevalence of larval digeneans in intertidal gastropods. The restricted distribution of the snail Heleobia australis along a 500 m transect in Cangrejo creek (Mar Chiquita, Argentina) provides a good opportunity to test the assumption that a study at spatial scale of 100s meters can detect spatiotemporal fluctuations of a larval digenean assemblage. To analyze that, 3600 specimens of H. australis were collected seasonally during the year 2011. A quantitative variation and a space-time interaction between sampling points and seasons of the year for the total prevalence of larval digeneans and snail’s densities were found, as well as a positive correlation with abiotic factors. These results revealed that the fluctuations in the community of larval digeneans of the snail H. australis can be detected at small spatial scale, using its natural distribution of 500 m. This study also highlights the importance of seasonality as a factor that must be considered in studies focused on the search for patterns structuring the communities of larval digeneans, at medium and large scales.