Seasonality of salmonid parasites from flow‐through aquaculture in northern Germany: Emphasis on pathogenicity of Diplostomum spp. metacercaria

Abstract

The aim of the present study was to identify the parasite fauna of cultured rainbow trout (Oncorhynchus mykiss Walbaum, 1792) and Arctic charr (Salvelinus alpinus (L.)) from a flow-through aquaculture system at Lake Tollense in northern Germany.The fish were sampled during different seasons in 2018 from an open freshwater raceway. For rainbow trout, 10 different parasite species were isolated, belonging to Monogenea (1), Cestoda (2), Crustacea (2) and Digenea (5), including the eye flukes Tylodelphys clavata Niewiadomska, 1984, Diplostomum pseudospathaceum and Diplostomum spathaceum (Rudolphi, 1819) Olsson, 1876, the latter representing a potential pathogenic species, which was molecularly identified and reported as a core species with prevalences of 80.0%-100.0% and high mean abundances of 42.8-55.0. Arctic charr only harboured T. clavata and D. spathaceum. Other taxa were found with low prevalence in the summer season exclusively, indicating strong seasonality of the detected parasites. Statistical correlation was positively tested for coherences of eye fluke burden and fish growth, weight and performance between seasons, recommending implementation of an enhanced aquaculture management for the surface waterdependent flow-through aquaculture system at Lake Tollense.

In-feed Praziquantel treatment of grass carp (Ctenopharyngodon idella) infected with eye flukes

“…This finding was confirmed by the lower average abundance of metacercariae in the heavier groups of fish in our study. On the other hand, Unger et al. (2022) proved that rainbow trout from open farm systems accumulate eye flukes over time and independent of the differences in resistance, getting exposed to a constant infection rate with the cercariae throughout the year.…”

“…This finding was confirmed by the lower average abundance of metacercariae in the heavier groups of fish in our study. On the other hand, Unger et al (2022) proved that rainbow trout from open farm systems accumulate eye flukes over time and independent of the differences in resistance, getting exposed to a constant infection rate with the cercariae throughout the year. PZQ is effective at treating the juvenile stages of digeneans in fish, with the treatment used to avoid detrimental health impacts, to maintain the market value, or to disrupt the parasite life cycle (Bader et al 2019).…”