The genus Catadiscus Cohn, 1904 has a total of 16 known species that infect the intestinal tract of reptiles, amphibians, and mollusks. However, Catadiscus has never been found in teleosts. The annual fish Austrolebias prognathus (Amato, 1986) and A. cheradophilus (Vaz-Ferreira, Sierra de Soriano & Scaglia de Paulete, 1965) were collected from temporary ponds in the southeast of Uruguay. The specimens found in the intestinal tract of these hosts were morphologically identified as Catadiscus uruguayensis Freitas & Lent, 1939, which until now were only known to infect amphibians. This work represents the first report of the genus Catadiscus infecting and developing in a fish host.
Spirometra Faust, Campbell et Kellogg, 1929 is a genus of cestodes belonging to the family Diphyllobothriidae. To date, amphibians, reptiles, and mammals are known second intermediate hosts of these parasites; humans can also be infected (the zoonotic disease is known as sparganosis or spirometrosis). Although the number of phylogenetic studies on Spirometra spp. has increased worldwide in recent years, there are few in South America. Specifically in Uruguay, molecular studies have shown that tapeworms of S. decipiens (Diesing, 1850) complexes 1 and 2 are present in this country. In this study, we characterised the larvae of Spirometra present in the annual fish Austrolebias charrua Costa et Cheffe. Phylogenetic analysis of the cytochrome c oxidase subunit I (COI) sequences of these larvae showed that they belong to S. decipiens complex 1. This is the first report of teleost fishes serving as a second intermediate host for tapeworms of the genus Spirometra in nature.
Silversides are renowned for their phenotypic plasticity with different populations coexisting as incipient species. The New World silverside Odontesthes argentinensis is an estuarine-resident fish with known populations inhabiting the Rio de la Plata estuary as well as coastal lagoons of Brazil, Uruguay and Argentina, where it constitutes an important resource for artisanal fisheries. Using classical morphometric analysis, we study six morphological variables to determine if there are differences between the New World silversides collected from two Uruguayan Atlantic coastal lagoons (Garzon and Rocha Lagoons), which communicate periodically with the ocean. In collaboration with artisanal fishermen, silversides were measured in fresh condition. After removing the size and allometric effect on the variables, Canonical Discriminant Analysis (DA) was applied to compare the morphometry of individuals collected in the two lagoons. Results supported the existence of two groups with values greater than 80% of accurate classification. The morphometric variables that contributed the most to this result were eye diameter, breadth of mouth, length from mouth tip to anal fin and length of pectoral fin. The first two morphometric variables are related to sensory perception and feeding, which could be indicators of an ecological segregation, conditioned by the characteristics of the environment, considering that the two coastal lagoons differ in their abiotic characteristics, most importantly in their hydrodynamic conditions. This work represents the first study of differences between two estuarine coastal lagoon populations of O. argentinensis.
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