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

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.

Mycotoxin production by three different toxigenic fungi genera on formulated abalone feed and the effect of an aquatic environment on fumonisins.

Mycotoxins are toxic secondary metabolites produced by various filamentous fungi, of which Fusarium, Aspergillus and Penicillium are the three main genera. Fusarium verticillioides is one of the most dominant toxigenic fungal species, associated with fumonisin contamination in grain-based feeds, such as compound abalone feed. Mycotoxin production is influenced by temperature and available nutrients. In this study the aims were: to determine if abalone feed as growth substrate favours mycotoxin production for toxigenic fungi; to determine the most effective temperature for fumonisin production by F. verticillioides on abalone feed; and to assess the effect of the aquatic environment on fumonisin-contaminated abalone feed. A total of 93 fungal isolates were inoculated onto abalone feed, including species belonging to the genera Fusarium, Aspergillus and Penicillium. Feed inoculated with F. verticillioides were incubated at two different temperatures and fumonisin-contaminated feed was submerged into seawater for 24 h. Results showed that mycotoxins were produced when abalone feed was inoculated with toxigenic fungi, and that F. verticillioides produced higher concentrations of fumonisins at a lower temperature. Submerging fumonisin-contaminated feed in seawater showed that this toxin leached into the seawater, lowering the risk of fumonisins to be consumed by abalone.