Oomycetes are a diverse group of fungus-like eukaryotic organisms, many of which are responsible for serious infections in both wild and cultured aquatic animals. Although oomyctes within the order Saprolegniales, such as Saprolegnia, Achlya, and Aphanomyces, may present with similar clinical signs, they differ notably in their pathogenicity, environmental preferences, and responses to antifungal treatments. . These differences have practical consequences for aquaculture, where empirical, broad-spectrum antifungal treatments often fail to resolve infections effectively, leading to economic losses and compromised animal welfare.
In this study, we report the first isolation of Achlya bisexualis from ornamental fish in South Africa and characterise the isolate using morphological, physiological, and molecular techniques. The species demonstrated unique growth responses across a temperature gradient, highlighting the need to consider individual species’ biology in disease diagnosis and control. When compared to closely related oomycetes, the variability in physiological traits reinforces that not all oomycetes respond uniformly to environmental stressors or treatments.
Accurate species identification improves aquaculture disease management by enabling targeted treatment protocols, avoiding in discriminate medication use, and informing biosecurity strategies. With molecular diagnostics becoming more accessible, routine identification of oomycetes at the species level should be integrated into standard health monitoring procedures. Such an approach not only improves treatment efficacy but also contributes to antimicrobial stewardship and sustainable aquaculture practices.
This study supports a growing body of evidence that emphasises the ecological and pathological diversity of oomycetes. Recognising and addressing species-specific traits is essential for the advancement of effective, evidence-based disease management in aquaculture systems.