Isolation, Characterization and Pathogenicity of Saprolegnia parasitica—Causal Agent of Saprolegniasis in Indian Major Carps

Saprolegnia species are responsible for an important fungal disease, saprolegniasis in Indian major carp. The present research work aimed to isolate, characterize, optimize and study the pathogenicity of Saprolegnia parasitica in Indian major carp. Four isolates of cotton mold were isolated from Indian major carp (Catla catla, Labeo rohita, and Cirrhinus mrigala) suffering from saprolegniasis, initially based on morphological attributes. Isolates were characterized by both morphological and molecular 18S rRNA methods. Constructed phylogenetic tree of four isolates suggested that the isolates are closely related to Saprolegnia parasitica (GenBank accession numbers are MW080657, MW050939, MW049353, and MW077678) and had a wide geographical region. The pathogenicity of Saprolegnia parasitica on Indian major carp experienced 100% cumulative mortality. The histopathological study of infected fishes showed ruptured epidermis, edema in the hypodermis, and degenerated myofibrillar cells. Saprolegnia parasitica is a highly pathogenic fungus for freshwater Indian major carp.