Abstract
The nematode Eustrongylides excisus is a parasite of freshwater fish- and fish-eating birds, with known differences on prevalence values among fish species. Thus, the present study aims to explore the hypothesis that the feeding behavior and the size of fish belonging to different trophic levels could explain such differences. For that, 14 sampling sites were selected to perform a fish parasitological survey on Lake Garda (Italy) during spring-summer 2020. Amplification of nuclear ribosomal internal transcribed spacer (ITS) rDNA sequences of nematodes morphologically ascribable to the genus Eustrongylides allowed to identify them as E. excisus. From the five studied fish species (Perca fluviatilis, Lepomis gibbous, Coregonus lavaretus, Alosa fallax lacustris and Micropterus salmoides), only three presented the parasite E. excisus: P. fluviatilis, L. gibbous and M. salmoides, with significant differences in prevalence values among species (p = 0.002). Additionally, there were differences in prevalence values within the same fish species captured from different sampling sites. Findings showed that mainly piscivorous fish were positive for E. excisus and how the prevalence was highest in M. salmoides. As regard the fish size, a negative correlation between body size and E. excisus was found in P. fluviatilis due to the feeding habit of juvenile perch which feed mainly zooplankton and benthic invertebrates (i.e., oligochaetes, which are the first intermediate hosts of E. excisus). The study findings advance novel knowledge in the field of pathogens of zoonotic importance in the aquatic environment.
Highlights
Providing original and novel knowledge, the present study aims to explore if feeding behaviour and size could explain the difference in prevalence values among fish species belonging to different trophic levels
All isolated parasite larvae were morphologically referred to the genus Eustrongylides spp. (Figures 2 and 3)
We found that mainly piscivorous fish were positive for E. excisus and that prevalence was highest in M. salmoides
Summary
Nematodes ascribable to the genus Eustrongylides Jagerskiold, 1909 (Family: Dioctophymatidae) are large, red, grossly visible parasites that infect numerous fish species and fish–eating birds [1]. Many species have been described within the genus but only three are considered valid: Eustrongylides tubifex, E. excisus, and E. ignotus [2]. Eustrongylid nematodes have been described in 17 orders of fish worldwide to date [6,7,8,9,10]. Predatory fish such as pikeperch (Sander lucioperca) and pike (Esox spp.), amphibians, and reptiles [2,11] may act as paratenic hosts and humans as accidental hosts [12]. Species of the genus Eustrongylides are freshwater fish–borne zoonotic nematodes, of which E. excisus is the most relevant species [13]
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