Aquatics Water Mold Infection Study Guide

Overview and Clinical Importance

Saprolegniosis (commonly called water mold infection or cotton wool disease) is one of the most economically significant oomycete infections affecting freshwater fish and their eggs worldwide. Caused primarily by species of the genus Saprolegnia (especially S. parasitica and S. diclina), this disease causes substantial mortality in aquaculture facilities, hatcheries, and wild fish populations. Understanding this pathogen is essential for the NAVLE as it represents a significant aquatic disease entity.

Taxonomic Classification: Despite being commonly referred to as a fungus, Saprolegnia is actually an oomycete (water mold) belonging to the Kingdom Stramenopila (Chromista), Phylum Oomycota. Oomycetes are more closely related to brown algae and diatoms than to true fungi. Key distinguishing features include cellulose-based cell walls (rather than chitin), diploid vegetative states, and biflagellate zoospores.

Etiology and Pathogen Characteristics

Causative Agents

The order Saprolegniales includes several genera that can cause disease in fish: Saprolegnia, Achlya, Aphanomyces, Leptolegnia, and Dictyuchus. The most pathogenic and commonly encountered species include: