Evaluation of physiological aspects and molecular identification of Saprolegnia isolates from rainbow trout (Oncorhynchus mykiss) and Caspian trout (Salmo trutta caspius) eggs based on RAPD- PCR

The genus of saprolegnia is one of the most important pathogenic aquatic fungi in farmed and wild fish. In the present study, fungal infected egss were collected from rainbow trout (Oncorhyncus mykiss) and Caspian trout (Salmo trutta caspius). After purification, 16 isolates were obtained (8 isolates from rainbow trout and 8 isolates from Caspian salmon, respectively). The isolates were then coded as R2 – R9 (rainbow trout) and S2 – S9 (Caspian trout).The registered DNA for S. parasitica (ACTT # 200048) and S. diclina (ACTT # 4206) were used and coded as R1 and S1, respectively. Based on the RAPD profile obtained all samples were divided to 3 groups and members of each group had more than 90% similarity among themselves. According to matrix of similarity and reference strains, the isolates were classified as three groups. Therefore, all of isolates in group 1 and 3 were S. parasitica and S. diclina, respectively, and the members of group 2 were known as Saprolegnia sp. The results of thermal resistance assessment showed that the isolates of rainbow trout and Caspian salmon eggs had slow growth in the temperature between 18 – 20 °C. Thus, R2 and S8 isolates had the lowest radial growth compared to other isolates. The isolates categorized in S. parasitica (group 1) created secoundry zoospores but not observed in two other groups. Thus, catenulated gamme was found in 78% and 55.55% isolates of rainbow trout and Caspian trout eggs, respectively. This study indicated that molecular methods were the best methods for identification of Saprolegnia spp. and it could be applied as a supplementary confirming method.