Cryopreservation of three Saprolegnia species (Oomycota): Preliminary evidence for the long-term archiving of water mould species.

Saprolegnia spp. water moulds are opportunistic pathogens that can cause economic losses to aquaculture. The diseases caused by them are difficult to control since use of the effective drug, malachite green oxalate, is no longer permitted in several regions (including the European Union and USA). To develop an effective control strategy, Saprolegnia isolates must be maintained in the laboratory. Cryopreservation is a useful solution for long-term maintenance; however, at present, there is no developed protocol for the cryopreservation of Saprolegnia spp. Here, we isolated and identified three Saprolegnia species, S. parasitica, S. australis and S. ferax, and developed a deep-freezing protocol that enables the long-term archiving of these species. The survival and growth rates of isolates kept at −80 °C for 3, 6, 9 and 12 months, were tested and compared among the species examined. Although the growth rates of frozen isolates were significantly lower than those of the control (i.e. non-frozen) isolates, the overall survival rate (>90%) indicated the effectiveness of the technique developed. Thus, the protocol developed appears to be a promising method for the long-term preservation of Saprolegnia isolates and may facilitate the creation of stock collections.