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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of these species and their determining factors, a large dataset composed by newly collected fish samples, published and unpublished data from previous studies by the authors in the region were analysed in relation to host and environmental variables.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. [ABSTRACT FROM AUTHOR]

• Fish age and size have a strong influence on the structure of parasite assemblages. • Similarity in parasite assemblages decreases as differences in host size increase. • Parasite communities in younger specimens are more heterogeneous and stochastic. • Ontogenetic change in parasite loads is enhanced by age-related asynchronic migrations. • Parasite tags must be used cautiously if asynchronous and divergent migrations occur. Several species of marine fishes perform seasonal migrations alternating foraging and spawning habitats during their life cycles. The knowledge of these movements is essential to define their population structure which is, in turn, necessary for a sustainable management of any fishery resource. Parasite tags have been extensively applied for stock identification and host migration assessment, proving to be excellent markers. However, ontogenetic changes in the structure of parasite assemblages must be considered since, due to ontogenetic cumulative patterns, differences between host length can lead to a misinterpretation of the patterns in this type of studies. The aim of this work was to evaluate the asynchronous migrations of the Argentine croaker Umbrina canosai , a demersal fish that inhabits coastal waters of Brazil, Uruguay and Argentina, as a cause of ontogenetic differences in parasite loads, considering its impact in the interpretation of migratory patterns when parasite assemblages are used as biological tags. A total of 254 specimens distributed into 8 samples (3 newly collected and 5 from previous study) with differences in mean length were examined for their metazoan parasites. Only long-lived parasites were used for comparisons between samples. A strong influence of fish length on the structure and composition of the parasite assemblages was observed across samples. Indeed, a clear pattern of similarity decay between parasite communities was evident as the differences in host length increased, demonstrating the importance of ontogenetic changes in the structure of parasites assemblages. On the other hand, differences in parasite assemblages were, most noticeably observed in young fish, indicating probable variations in migratory routes, distance traveled and/or latitude reached, depending on environmental conditions and age. Consequently, differences among fish length classes must be considered when using parasite tags for those resources with temporally and spatially variable migratory patterns, especially when different cohorts are compared. [ABSTRACT FROM AUTHOR]

We assessed temporal variability in parasite infections of rough scad (Trachurus lathami) in 3 samples from Miramar (MI) in 2008, separated by periods of 1 mo, and 2 samples from Villa Gesell (VG), 1 each in 2008 and 2009 (Buenos Aires Province, Argentina), respectively. A sample was also obtained from Cabo Frio (CF) (Brazil) in 2009 to compare differences in parasite communities between fish from this locality and each Argentinean locality. All rough scad were parasitized by at least 1 of 27 parasite species. Similarity-based multivariate analysis revealed significant differences between localities, but temporal homogeneity in each Argentinean locality. Overall, prevalence and abundance of parasite species were most similar between samples from MI and VG, while the greatest differences occurred between samples from MI and CF. A canonical analysis of principal coordinates showed significant differences among samples. Grillotia carvajalregorum was the most important species in determining the position of Argentinean samples, especially those from MI, while Ectenurus virgulus , Raphidascaris sp., and Hysterothylacium sp. were the most important species related to fish from CF. The parasite assemblage of T. lathami showed a notable temporal persistence within the same locality and a high variability at the spatial scale, suggesting the existence of 3 independent stocks of T. lathami in South Atlantic waters.