Morphological and molecular characterization of Saprolegnia spp. from Himalayan snow trout, Schizothorax richardsonii: A case study report

Snow trout, Schizothorax richardsonii, in early as well as in advance life stages are highly susceptible to Saprolegnia spp. infections. In the present study, we aimed to identify the Saprolegnia spp. from different life stages of infected snow trout eggs, juveniles, and adults from two geographic regions, Bhimtal and Champawat of Central Himalaya, India. Morphological identification was carried out by microscopic observation of life stages of Saprolegnia. For the molecular characterization, the internal transcribed spacer region (ITS) was amplified using universal primers ITS 1 and ITS 4. On the basis of the morphological and molecular findings, we have identified two Saprolegnia species from snow trout, i.e., Saprolegnia parasitica from eggs and adults; and S. australis from eggs and juveniles. In particular, S. parasitica was isolated from both geographical regions and S. australis only from Bhimtal, where a comparatively higher temperature regime prevails. An in-vitro experiment was conducted to study the growth of Saprolegnia spp. in varying incubation temperatures. The results confirmed that S. australis could not thrive at or below 7 degrees C, whereas S. parasitica could grow within the temperature range of 4-20 degrees C.