The first detection and in vivo pathogenicity characterization of Saprolegnia delica from Kashmir Himalayas

Abstract Saprolegniosis caused by ubiquitous oomycetes pathogen Saprolegnia spp. poses a serious threat to the welfare and fortitude of the fish industry, therefore having potential to inflict severe socio-economic losses to the stakeholders involved in aquaculture trade. In this study, Saprolegnia delica was isolated for the first time from naturally infected farmed fish in Kashmir Himalayas, India. The isolate was identified by a combination of (macro and micro morphological) and molecular approaches, the latter involving sequencing of the entire internal transcribed spacer region. The identified S. delica was further evaluated for its pathogenic potential in an artificial setting by using in vivo models, Scale Carp (Cyprinis carpio communis) fingerlings and Rainbow Trout (Oncorhynchus mykiss) eggs. We used intraperitoneal injection and bath immersion means for challenging the host, our results indicated that S. delica is highly pathogenic to both, the fish fingerlings of scale carp and the eggs of rainbow trout. Also, intraperitoneal inoculation was observed to cause higher mortality (55%) in scale carp fingerlings compared to the bath immersion method. The postmortem and histopathology analyses revealed that S. delica is severely infecting skin, gills, eyes and other visceral organs, which led to the infection of multiple organs causing high mortality. However, severity of the disease depends on the route of infection in fingerlings, the time of exposure and the concentration of spores inoculated to eggs. The study presents the first isolation and detection of S. delica infecting rainbow trout in fish farm of Kashmir valley, hence, provides a way forward for the establishment of management strategies aimed at controlling saprolegniosis.