Towards an in situ non-lethal rapid test to accurately detect the presence of the nematode parasite, Anguillicoloides crassus, in European eel, Anguilla anguilla

Abstract

Anguillicoloides crassus is an invasive nematode parasite of the critically endangered European eel, Anguilla anguilla, and possibly one of the primary drivers of eel population collapse, impacting many features of eel physiology and life history. Early detection of the parasite is vital to limit the spread of A. crassus, to assess its potential impact on spawning biomass. However accurate diagnosis of infection could only be achieved via necropsy. To support eel fisheries management we developed a rapid, non-lethal, minimally invasive and in situ DNA-based method to infer the presence of the parasite in the swim bladder. Screening of 131 wild eels was undertaken between 2017 and 2019 in Ireland and UK to validate the procedure. DNA extractions and PCR were conducted using both a Qiagen Stool kit and in situ using Whatman qualitative filter paper No1 and a miniPCR DNA Discovery-System™. Primers were specifically designed to target the cytochrome oxidase mtDNA gene region and in situ extraction and amplification takes approximately 3 h for up to 16 individuals. Our in-situ diagnostic procedure demonstrated positive predictive values at 96% and negative predictive values at 87% by comparison to necropsy data. Our method could be a valuable tool in the hands of fisheries managers to enable infection control and help protect this iconic but critically endangered species.

Effects of preservation by ethanol on δ13C and δ15N of three tissues of the critically endangered European eel Anguilla anguilla

“…In contemporary sampling programmes where trophic analyses of eel are required, muscle tissue can be compared directly with fin and mucus, as there are no significant differences in the δ 13 C and δ 15 N values of these tissues within individuals (Boardman et al ., 2022). Non‐lethal tissue sampling is thus recommended due to their critically endangered status ( e.g ., Boardman et al ., 2022), especially as this can now be coupled with non‐lethal screening for the invasive nematode parasite Anguillicoloides crassus (De Noia et al ., 2022). Nevertheless, eel SIA is still often based on dorsal muscle, where tissue samples are usually excised from euthanised fish (Capoccioni et al ., 2021; Parzanini et al ., 2021).…”

Minimally Invasive Collection of Biometric Data Including Maturation Stage on European Eel Using Photography

“…2003; De Noia et al. 2022). Harmless methods are of special importance if the data are acquired for monitoring purposes and the respective fish are supposed to be released with no harm, as is the case, for example, in electrofishing surveys or mark–recapture studies.…”

“…Even though in some cases it may be necessary to sacrifice eels for certain methodologies (e.g., age reading, otolith microchemistry, or certain contaminant analyses), it is generally desirable to collect biometric data on live animals with limited harm by using minimally invasive methods to avoid the unnecessary sacrifice of these endangered specimens. This would complement available minimally invasive methods for the determination of muscle fat content (Pohlmann et al 2019), salinity-habitat history (Bertolini et al 2022), and parasite infection or damage (Beregi et al 1998;Crean et al 2003;De Noia et al 2022). Harmless methods are of special importance if the data are acquired for monitoring purposes and the respective fish are supposed to be released with no harm, as is the case, for example, in electrofishing surveys or mark-recapture studies.…”