First Record of the Water Mold Achlya bisexualis (Saprolegniaceae) Isolated from Ornamental Fish in South Africa

Abstract

The order Saprolegniales (Class Oomycota) is a group of fungus-like eukaryotic microorganisms that have been associated with infections in fish and fish eggs. Infections with microorganisms from this order are clearly evident because they have a cotton wool-like appearance. The aim of this study was to characterize and identify an oomycete that was isolated from the eye of an Orange Blotched Peacock Cichlid Aulonacara sp. A sample of cotton wool-like mycelia was isolated and single-spore isolations were conducted. Molecular characterization and phylogenetic analysis of the ITS1-5.8-ITS2 rDNA region for all isolates were used for species identification. Following molecular identification, one isolate was used to culture and characterize the reproductive structures. Physiological characterization entailed incubating the isolate on potato dextrose agar (PDA) at five different temperatures, ranging from 5°C to 25°C, to monitor growth rates. A multiple sequence alignment showed 100% similarity between all of the single-spore isolates and alignment with other Achlya bisexualis strains. Long, coarse hyphae with zoosporangia and gemmae typical of the order Saprolegniales were observed with an optimal growth rate at 25°C. The oomycete that was isolated from an Orange Blotched Peacock Cichlid was identified as A. bisexualis, the first record of this species in South Africa.

Efficacy of acriflavin chloride and Melaleuca alternifolia extract against Saprolegnia parasitica infection in Pterophyllum scalare

“…A study performed in Korea from fish identified seven isolates of saprolegniosis pathogens, morphological and molecular phylogenetic analysis of which permitted them to be identified as Achlya americana and A. bisexualis (Choi et al, 2019). Oomycetes isolated from cichlids in South Africa have been identified as A. bisexualis (Greeff-Laubscher et al, 2019).…”

“…Molecular studies and phylogenetic analysis of the DNA region of isolates are used to identify pathogens. Mycological studies involve incubation of isolates on potato agar dextrose (PDA) at different temperatures, from 5 to 25 °C to monitor growth rates (Greeff-Laubscher et al, 2019).…”