Anthropogenic spreading ofanguillid herpesvirus 1by stocking of infected farmed European eels,Anguilla anguilla(L.), in the Schlei fjord in northern Germany

Abstract

The Schlei fjord in northern Germany is the recipient water of a comprehensive eel, Anguilla anguilla (L.), stocking programme. Since 2015, stocked eels become alizarin red S marked, but to date no control mechanism is implemented in this stock enhancement measure to prevent anthropogenic spreading of diseases. Consequentially, it was possible that farmed stocking cohorts of 2015 and 2016 (in total ca. 1040 kg) were subsequently tested positive for anguillid herpesvirus 1 (AngHV 1). For this study, 100 eels [total length (TL) 24.3-72.9 cm, age ca. 1-6 years] were caught in 2016 and investigated with regard to AngHV 1 infection, parasite load (Anguillicoloides crassus) and body conditions. 68% of the eels were found to be virus positive while larger specimens were more often infected. In addition, a fitted generalized linear model (area under the curve = 0.741) demonstrated that an increase in individual TL is accompanied with an increased risk of clinically relevant virus loads. Anguillicoloides crassus turned out to be an important stressor for eels, because parasite and virus load revealed a significant positive correlation. The results of this study evidently show the urgent need of a disease containment strategy for eel stocking programmes.

Important questions to progress science and sustainable management of anguillid eels

“…At present, there is no evidence that stocked eels contribute to the spawning stock (ICES, 2011, 2016c) but it can increase silver eel escapement from river basins (Pratt & Threader, 2011; Wickström, 2001). Habitat, glass eel condition and density‐dependent factors may impact stocking success (Dekker, 2015; Marohn et al, 2013; Simon & Dörner, 2014) and potential risks include altering local genetic structure (Als et al, 2011; Pavey et al, 2015; Pawson, 2012), introducing alien species (Marohn et al, 2014) diseases and parasites (Jakob et al, 2016; Kullmann et al, 2017; Pratt et al, 2019), and altering sex ratios and growth patterns (Côté et al, 2009; ICES, 2011). Several studies (without natural controls) demonstrate deviations from expected spawning migration patterns for stocked eels (Prigge et al, 2013; Sjöberg et al, 2017; Westin, 2003).…”

Genomes of Anguillid Herpesvirus 1 Strains Reveal Evolutionary Disparities and Low Genetic Diversity in the Genus Cyprinivirus

“…However, these differences may not only reflect the fundamental differences in biology but also the epidemiological circumstances linked to anthropogenic influence and possibly a certain amount of methodological bias. Firstly, it is likely that recent anthropogenic activities, including international trade associated with increased globalization, have played a significant role in the rapid spread of cypriniviruses [ 120 , 121 , 122 , 123 , 124 , 125 , 126 ], and thus their widespread distribution may only be a very recent phenomenon. Secondly, the sequence data in the present study may be biased towards pathogenic strains that have successfully adapted to aquaculture environments and are responsible for severe clinical outbreaks, thus leading to underestimations of cyprinivirus diversity.…”

Molecular ontogeny of larval immunity in European eel at increasing temperatures

“…Tail tissues (~10 mm of the body end) were sampled from 10 euthanized (with 0.5g l -1 of MS-222) European glass eels during routine health checks at the Veterinary University Hannover, Germany. The fish from which the explants had been collected were confirmed to be AngHV-1 negative by qPCR described earlier [9]. The explants were collected into PBS supplemented with 10 IU ml-1 penicillin, 100 mg ml -1 streptomycin, 100 mg ml -1 gentamycin, and 1 mg ml -1 amphotericin B (all Sigma), and thereafter placed on ice.…”

“…Knowledge of the development of the immune system is hence needed to design preventative methods against pathogens such as the anguillid herpesvirus 1 (AngHV-1) and the parasite Anguillicoloides crassus, which pose an important threat to the European eel [9], in order to prevent losses in forthcoming aquaculture hatcheries. The European eel is a commercially high-value fish species with a long tradition in European fisheries and fish farming.…”