Parasitic nematodes can infect both wild and cultivated fish species and may be the source of many diseases. The consumption of raw fish meat in many countries has been the responsible of nematode related zoonosis. Knowing the risk of consumption of contaminated fish by the local communities, the main goal of this paper is to quantify and report the presence of larvae with zoonotic potential of Contracaecum spp. and Eustrongylides spp. found in two exotic fish species from the Tramandaí River Basin in southern Brazil. The sample sites were two lagoons of the basin, the Itapeva lagoon and Palmital lagoon, sampled in the period of April 2018. Forty specimens of Acestrorhynchus pantaneiro and twenty specimens of Trachelyopterus lucenai were examined. A. pantaneiro presented a 58% and 4% prevalence and a mean intensity of 3.17 and 1 for Contracaecum spp. and Eustrongylides spp., respectively. Meanwhile T. lucenai presented a prevalence of 70% and 5% and a mean intensity of 1.92 and 1 of Contracaecum spp. larvae and Eustrongylides spp. larvae, respectively. Although larvae of Contracaeucum spp. are reported only in the literature in experimental infections, they were able to complete their biological cycle in some mammals with certain pathogeneses. However, larvae of Eustrongylides spp. infect humans, as reported in the literature, causing severe damage to the intestinal tract. Knowing that local populations may be at risk, we recommend that all prophylactic measures be taken in relation to fish consumption. This study also contributes to the knowledge concerning the parasitic fauna of the host species studied.

The helminths belonging to the class Trematoda have great importance in ichthyoparasitology, and the subclass Digenea includes parasites with zoonotic potential. The family Heterophyidae is responsible for the heterophyiasis and, in Brazil, this disease is caused by the trematode genera Ascocotyle (Phagicola), commonly known as phagicolosis, both related to the fish-to-birds/mammals cycle. Clinostomum (belonging to the family Clinostomidae) has its larval stage in fish musculature and piscivorous birds as definitive hosts. It may parasitize humans accidentally, causing parasitic laryngopharyngitis and death by asphyxia. This study aims to quantify the presence of digenetic Heterophyidae and Clinostomidae parasites with zoonotic potential in fish from the Tramandaí River basin, in the state of Rio Grande do Sul, Brazil. The fish were purchased from fishermen from Terra de Areia/RS, from July 2016 to May 2017. The search for parasites was carried out by performing a necropsy on the fish. The digenetic parasites were preserved, stained and mounted on microscope slides for identification. Parasitological indices were calculated. Astyanax spp. Were positive for Ascocotyle whereas Geophagus brasiliensis was infected by Clinostomum sp. Therefore, the results suggest a risk of infection to the consumer population in the region.