The fish sampled in this study were captured in seasonal collections samplings, conducted between May 2006 and February 2007 in 15 stretches of the Corrientes stream basin, Patos lagoon system, Rio Grande do Sul state, Brazil. A total of 8088 specimens were collected, belonging to nine orders, 24 families and 68 species. In general, the ichthyofauna in this basin has the same pattern recognized for Neotropical rivers with predominance of Characiformes and Siluriformes orders and a high representative of the Characidae and Loricariidae families.

During the period 2010-2012, eighty individuals of Calidris fuscicollis (Vieillot, 1819) were collected on the southern coast of Rio Grande do Sul, Brazil, with the objective of determining the presence of feather mites. Of the 80 birds examined, 32.5% were infested by mites, identified as Avenzoaria calidridis (Oudemans, 1904) Palavras-chave: ácaros plumícolas, Avenzoariidae, Pterolichidae, Alloptidae, maçarico-de-sobre-branco.

During April and September from 2010 to 2012, 80 birds of the species Calidris fuscicollis (white-rumped sandpiper) were collected for parasitological studies in the southern coast of Rio Grande do Sul, under ICMBIO license No. 26234-1. For ectoparasite collection, the birds were first submerged in water with detergent. The parasites found were fixed in 70% alcohol, cleared in 10% potassium hydroxide and mounted in Canada balsam. Of 80 birds examined, 79% were parasitized. Actornithophilus umbrinus (47.5%), Actornithophilus lacustris (37.5%), Actornithophilus spp. (13.75%), Carduiceps zonarius (26.25%), Lunaceps incoenis (27.5%), and Lunaceps spp. (16.25%) were the species found with their respective prevalence. We record for the first time parasitism by chewing lice in Calidris fuscicollis.

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