reasons for population settlement along the Norwegian coasts. Because cod fishery in Norway is seasonal between January and April, in addition and there is yearly variation in the cod fishing quota, the start of commercial cod aquaculture was encouraged. Cod farming bloomed in the mid-2000 reaching 533 farming licenses in 2008 and a total production of 21 240 tons in 2010. However, this industry was not to last, and the production started to drop until a total collapse in 2014. Several reasons led to this dramatic failure; juvenile deformities and early sexual maturation induced mediocre growth rates and elevated mortalities. In addition, disease outbreaks were also an important contributing reason to the collapse of cod farming in Norway. Two notifiable diseases dominated, franciselliosis and viral nervous necrosis (VNN). Bacterial disease francisellosis caused by Francisella noatunensis resulted in massive losses with no effective vaccine or treatment available. VNN caused by betanodavirus had similar consequences. The aim of this study was to screen migrating and stationary wild cod for these two pathogens to evaluate the risk of transmission to farmed cod before attempting the restoration of large-scale cod aquaculture.
Sampling: Sampling of migrating Atlantic cod was conducted from 2019 to 2021 by Nord University staff along the coast of Norway from Ålesund (n=200), Myre (n=1200) and Båtsfjord (n=200). Sampling of stationary wild cod at 8 sites from Bergen in the south to Tromsø in the north was performed in 2022 (n=500). Brain (for betanodavirus) and head-kidney (for Francisella) samples were collected for qPCR analysis. RNA extraction from brain and kidney samples was performed using E.Z.N.A.® Total RNA Kit (Omega BIO-TEK) according to manufacturer’s recommendations, and RNA were kept in -80°C until RT-qPCR analysis.
Oligonucleotide primers and hybridization probes: Assays for screening utilized in the study comprised of betanodavirus (Korsnes et al. 2005), Francisella nuatonensis (Ottem et al. 2008). In addition, a reference gene (elongation factor) was used as quality control of RNA (Mittelholzer et al. 2008). The amplification was performed using a one-step mastermix (qScript™ XLT One-Step RT-qPCR ToughMix® Quantabio). All RT-qPCR reactions were performed on a LightCycler 96 (Roche) and results analyzed by instrument software.
Prevalence of pathogens was low. So far, out of 1 600 kidney samples from migrating cod, only 10 came out positive for Francisella and none for nodavirus. Results from stationary cod are under processing. Complete set of results will be presented.
Acknowledgements
The study is part of the SmitteRisk research project, funded by RFF Nordland.