Abstract
Metacercariae of Diplostomidae are widely distributed in America and may cause diplostomiasis, an ocular disease in fishes. The aim of this study is to report the occurrence of metacercariae of Austrodiplostomum compactum in Plagioscion squamosissimus (non-native fish species) from Nova Avanhandava Reservoir, Tietê River, Brazil and an explanation for the high infection rates with this parasite in the Paraná River Basin is proposed. Eyes of 70 hosts were examined, the metacercariae were preserved and identified. The prevalence (P), mean intensity of infection (MII) ± standard deviation, mean abundance (MA) ± standard deviation, were calculated and a bibliographic review was performed. There was no difference in parasitism between male and female hosts. The values of P = 80%, MII = 21.55 ± 3.25 and MA = 17.24 ± 2.91 were high, as in most studies in areas where P. squamosissimus were introduced, while these values were low in areas of natural occurrence. This may be explained by the genetic susceptibility of the host to the parasite. The entire population of P. squamosissimus from the Upper Paraná has been founded by a few specimens, resulting in very low genetic variability. Consequently, the population may be highly susceptible to A. compactum.
Highlights
Metacercariae of Diplostomidae are widely distributed in the Americas (Ramos et al 2013, García-Varela et al 2016)
The aim of the present study was to report the occurrence of metacercariae of A. compactum in P. squamosissimus from the Bonito River, in the Nova Avanhandava reservoir, Lower Tietê River, State of São Paulo, Brazil, and to propose an alternative explanation for the high rate of parasitic infection in areas where P. squamosissimus were introduced
Morphometric analysis of the metacercariae was carried out using a computerized system for image analysis with differential interference contrast (DIC) (Leica Application Suite, V3; Leica Microsystems, Wetzlar, Germany) and the identification of the parasite was based on Ostrowski de Núñez (2017)
Summary
Metacercariae of Diplostomidae are widely distributed in the Americas (Ramos et al 2013, García-Varela et al 2016). Ocular diplostomiasis is a parasitic disease that affects reared and wild fish (Pinto & Melo 2013) caused by metacercariae, which at high densities may result in blindness and retarded development, as well as facilitating predation by piscivorous birds (Shariff et al 1980, Corrêa et al 2014). In South America, diplostomiasis is mainly caused by species of the genus Austrodiplostomum Szidat & Nani, 1951. The adults of Austrodiplostomum compactum (Lutz, 1928) were recorded in several countries from America (Argentina, Brazil, U.S.A., Mexico and Venezuela) inhabit the intestine of the piscivorous birds Nannopterum auritus (Lesson, 1831) (=Phalacrocorax auritus) and Nannopterum brasilianus (Gmelin, 1789) (=Phalacrocorax brasilianus) (Szidat & Nani 1951, Dubois 1968, Ostrowski de Núñez 1982, 2017, Dronen 2009, Monteiro et al 2011, O’Hear et al 2014, Garcia-Varela et al 2016, Rosser et al 2016).
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