Abstract
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.
Highlights
The Saprolegnia spp. (Heterokontophyta: Oomycota), known as water moulds, are endemic in most freshwater habitats worldwide (van West, 2006)
Saprolegnia spp. are generally a secondary pathogens, under appropriate conditions, they can act as primary pathogens, causing substantial economic losses to aquaculture (Wuensch et al, 2018); this is of particular concern for fish farms where fish eggs, fish fry and adult fish are affected by infection with water mould (Eiras et al, 2008; Woo and Bruno, 2011)
The survival rate of the strains S. parasitica and S. australis strains was two out of three after 6 months of deep-freezing, while that of the strain S. ferax was three of three; all surviving strains colonised the entire medium by day 4 (Fig. 2B)
Summary
The Saprolegnia spp. (Heterokontophyta: Oomycota), known as water moulds, are endemic in most freshwater habitats worldwide (van West, 2006). Saprolegnia spp. are generally a secondary pathogens, under appropriate conditions, they can act as primary pathogens, causing substantial economic losses to aquaculture (Wuensch et al, 2018); this is of particular concern for fish farms where fish eggs, fish fry and adult fish are affected by infection with water mould (Eiras et al, 2008; Woo and Bruno, 2011). There are several reported methods for culturing Saprolegnia. El-Nagdy and Abdel-Hafez (1990) and Khallil et al (1991) used hemp seed as bait, and glucose or cellulose Czapek Dox agar as culture medium. Hussein et al (2001) cultured Saprolegnia spp. on glucose-yeast (GY) medium containing ampicillin and streptomycin. El-Nagdy and Abdel-Hafez (1990) and Khallil et al (1991) used hemp seed as bait, and glucose or cellulose Czapek Dox agar as culture medium. Hussein et al (2001) cultured Saprolegnia spp. on glucose-yeast (GY) medium containing ampicillin and streptomycin. Carbajal-Gonzalez et al (2011) used tryptic soy agar (TSA) and sheep blood agar for culturing, whereas Shin et al (2017)
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