Genetic identification of Anisakis spp. (Nematoda: Anisakidae) from cetaceans of the Southwestern Atlantic Ocean: ecological and zoogeographical implications.

Adult Anisakis Dujardin, 1845 were found in two specimens of killer whale Orcinus orca and one specimen of franciscana Pontoporia blainvillei stranded from off the coast of Buenos Aires Province, Argentina. Genetic identification of the nematodes (N = 144) was performed by sequence analysis of the mitochondrial (mtDNA cox2) and the nuclear (nas 10 nDNA) gene loci. Anisakis pegreffii and Anisakis berlandi were detected in the two individuals of O. orca, while Anisakis typica and A. pegreffii were identified in P. blainvillei. Morphological and morphometric analysis also carried out on adult specimens of A. pegreffii and A. berlandi has allowed to underlining the usefulness of genetic/molecular markers in their recognition. This represents the first record of A. pegreffii in O. orca and P. blainvillei and of A. berlandi in O. orca. This is also the first sympatric and syntopic occurrence, as adults, of A. pegreffii and A. berlandi from the Austral Region of the Atlantic Ocean waters. These results provide insights into the knowledge of the host ranges and geographical distribution of these parasites in the basin waters of the region. Pontoporia blainvillei showed low abundance values of infection with Anisakis spp., which is the general pattern for coastal dolphins in the area, whereas O. orca harboured higher abundance of Anisakis spp. than those previously recorded among cetacean species in the Argentine Sea. Differences in the Anisakis spp. distribution and their parasitic loads, observed among the three host specimens, are discussed in relation to the oceanographic parameters, as well as to the host ecology. The usefulness of genetic/molecular markers in the recognition of adults of the sibling species A. pegreffii and A. berlandi with considerable overlapping in morphometric and morphological characters was underlined. The distribution of Anisakis species from Southwestern Atlantic waters is discussed in relation to their value as indicators for studies on the zoogeography of their hosts at a regional-scale level.

Distribution of parasites of slimy sculpin Cottus cognatus Richardson, 1836 (Scorpaeniformes: Cottidae) in the Athabasca drainage, Alberta, Canada, and their relation to water quality.

The composition and diversity of parasite communities are useful tools to characterise ecosystem health and integrity. Environmental disturbances may affect parasite infection in fish directly, by their effects on the free-living stages, or indirectly, on the intermediate hosts. Slimy sculpins, Cottus cognatus, a small fish inhabiting cold waters of North America, have been considered as sentinels due to their limited mobility, often occupying relatively small areas throughout their lives and thus reflecting the local environment. Ninety-six specimens of C. cognatus were sampled from four tributaries of the Athabasca River to assess patterns of helminth parasite community structure in this fish and to study the composition and diversity of its parasite communities in relation to water quality. The localities included single samples from High Hills, Horse and Dunkirk rivers, and two from the Steepbank River. Twelve metazoan parasite species were found, most of them being larval forms. Significant differences occurred in the structure and composition of parasite assemblages of sculpins from the tributaries, although similarities were observed in connected and nearby sites. Parasite communities were influenced mainly by a combination of local environmental conditions, distance and connectivity, and were separated based on the distribution and abundance of autogenic and allogenic parasites. Water quality appeared to influence the distribution of trematode species that use gastropods as intermediate hosts, while proximity and connectivity of sites led to sharing allogenic parasite species in slimy sculpin.

Profilicollis chasmagnathi (Acanthocephala) parasitizing freshwater fishes: paratenicity and an exception to the phylogenetic conservatism of the genus?

Polymorphid acanthocephalans are parasites of marine mammals, waterfowl and ichthyophagous birds. Among these, the genus Profilicollis is known to use exclusively decapods as intermediate hosts. Here, we report the first record of living cystacanths of Profilicollis parasitizing the body cavity of a fish host, Oligosarcus jenynsii, inhabiting the freshwater section of an estuarial system, Mar Chiquita coastal lagoon, in south-east Buenos Aires Province, Argentina. In this environment, cystacanths of Profilicollis chasmagnathi have been previously recorded infecting decapod crabs and as transient accidental infections in the gut of some carcinophagous fishes. In the present study, larvae from the crab Neohelice granulata, from the intestine of the estuarine fish Odontesthes argentinensis and from the body cavity of O. jenynsii were morphologically and genetically compared, confirming their identity as P. chasmagnathi, a species characteristic of estuaries and marine coasts along Argentina, Uruguay and Chile. These findings can be interpreted as a possible case of incipient paratenicity for Profilicollis, and a colonization event of freshwater habitats, probably promoted by the highly variable conditions, typical of ecotonal environments. In addition, cystacanths of the genus Polymorphus were also found in O. jenynsii, representing the first record of this genus in Oligosarcus from Argentina.

Assessing the role of host traits as drivers of the abundance of long-lived parasites in fish-stock assessment studies.

In order to identify the best tools for stock assessment studies using fish parasites as biological indicators, different host traits (size, mass and age and their interaction with sex) were evaluated as descriptors of cumulative patterns of both parasite abundance and infracommunity species richness. The effect of such variables was analysed for a sample of 265 specimens of Percophis brasiliensis caught in the Argentine Sea. The abundances and species richness were modelled using generalized linear mixed models (GLMMs) with negative binomial and Poisson distribution respectively. Due to collinearity, separate models were fitted for each of the three main explanatory variables (length, mass and age) to identify the optimal set of factors determining the parasite burdens. Optimal GLMMs were selected on the basis of the lowest Akaike information criteria, residual information and simulation studies based on 10 000 iterations. Results indicated that the covariates length and sex consistently appeared in the most parsimonious models suggesting that fish length seems to be a slightly better predictor than age or mass. The biological causes of these patterns are discussed. It is recommended to use fish length as a measure of growth and to restrict comparisons with fish of similar length or to incorporate length as covariate when comparing parasite burdens. Host sex should be also taken into account for those species sexually dimorphic in terms of morphology, behaviour or growth rates.

Homogeneity of parasite assemblages of Dules auriga (Serranidae) in hydrographically heterogeneous sites.

Parasite assemblages of Dules auriga are described for the first time from samples caught during research cruises in two localities of the Argentine-Uruguayan Common Fishing Zone (AUCFZ) and are compared with four additional samples collected by commercial catches from the same region. A total of 178 fish were examined and 13 parasite species were found. This showed low species richness, a condition observed in some other small benthic species at a low trophic level. The composition of the parasite fauna was similar to those found on other host species in the region, sharing the same set of dominant species with other sympatric fishes, which have been identified as both typical and as indicators of this ecoregion: Grillotia carvajalregorum, Corynosoma australe and Hysterothylacium sp. Multivariate similarity analyses at the infracommunity and the component community levels indicated that the two samples caught at different latitudes in the AUCFZ display almost identical parasite assemblages. This repeatability in assemblage structure was also observed across samples from commercial catches. The homogeneity of the parasite assemblages is considered to be an intrinsic property of fish inhabiting the AUCFZ, independent of their ecology and trophic level.

Fish trophic level and the similarity of non-specific larval parasite assemblages.

Whereas the effect of parasites on food webs is increasingly recognised and has been extensively measured and modelled, the effect of food webs on the structure of parasite assemblages has not been quantified in a similar way. Here, we apply the concept of decay in community similarity with increasing distance, previously used for parasites in geographical, phylogenetic and ontogenetic contexts, to differences in the trophic level (TL) based on diet composition of fishes. It is proposed as an accurate quantitative method to measure rates of assemblage change as a function of host feeding habits and is applied, to our knowledge for the first time, across host species in marine waters. We focused on a suite of 15 species of trophically-transmitted and non-specific larval helminths across 16 fish species (1783 specimens, six orders, 14 families) with different sizes and TLs, gathered from the same ecosystem. Not all host species harboured the same number and types of parasites, reflecting the differences in their ecological characteristics. Using differences in TL and body length as measurements of size and trophic distances, we found that similarity at both infracommunity and component community levels showed a very clear decay pattern, based on parasite abundance and relative abundance, with increasing distance in TL, but was not related to changes in fish size, with TL thus emerging as the main explanatory factor for similarity of parasite assemblages. Furthermore, the relationships between host TL and assemblage similarity allowed identification of fishes for which the TL was under- or over-estimated and prediction of the TL of host species based on parasite data alone.