DAO prepress abstract  -  doi: 10.3354/dao01916

ABSTRACT: Coldwater strawberry disease (CWSD) or Red mark syndrome, is a severe dermatitis affecting rainbow trout (O. mykiss). The condition, which presents as multifocal-raised lesions on the flanks of affected fish, was first diagnosed in Scotland in 2003 and has since spread to England and Wales. Results of field investigations indicated the condition had an infectious aetiology, with outbreaks in England linked to movements of live fish from affected sites in Scotland. Transmission trials confirmed these results, with 11/149 and 106/159 naïve rainbow trout displaying CWSD-characteristic lesions 104-106 days after being cohabited with CWSD-affected fish from two farms (Farm B from England and Farm C from Wales respectively). The condition apparently has a long latency, with the first characteristic lesions in the previously naïve fish not definitively observed until 65 days (650 day-degrees) post-contact with affected fish. Affected fish from both outbreak investigations and the infection trial were examined for the presence of viruses, oomycetes, parasites and bacteria using a combination of techniques and methodologies (including culture-independent cloning of PCR-amplifiedbacterial 16S rRNA genes from lesions), with no potentially causative infectious agent consistently identified. The majority of the cloned phylotypes from both lesion and negative control skin samples were assigned to Acidovax-like β-Proteobacteria and Methylobacter-like α-Proteobacteria