Vesieroosi

Vesieroosi, also known as *Vesiroosi* or *Vesiroosi disease*, is a fungal infection primarily affecting fish, particularly in freshwater aquaculture systems. The disease is caused by the fungus *Saprolegnia parasitica*, a member of the oomycete group, which is distinct from true fungi but behaves similarly in terms of pathogenicity. Vesieroosi is most commonly observed in salmonid species such as trout and salmon, though it can also impact other fish, amphibians, and even aquatic invertebrates.

The infection typically begins when fish experience physical damage to their skin or gills, often due to handling, poor water quality, or parasitic infestations. The fungus then attaches to the exposed tissue, forming cottony, white to grayish growths that resemble cotton wool. These growths can spread rapidly, leading to severe tissue damage, secondary bacterial infections, and, in advanced cases, death. Environmental factors such as cold water temperatures, low oxygen levels, and high organic load exacerbate the risk of infection.

Prevention of Vesieroosi relies on maintaining optimal water quality, including proper aeration, filtration, and regular monitoring of ammonia, nitrite, and nitrate levels. Minimizing physical stress on fish, such as reducing handling and ensuring proper stocking densities, also helps reduce susceptibility. In affected systems, treatments may involve mechanical removal of infected tissue, application of antifungal agents like malachite green (though its use is regulated in many regions), or improving water conditions to inhibit fungal growth. Quarantine and disinfection of equipment and tanks are critical in controlling outbreaks.

While Vesieroosi is not directly transmissible to humans, it highlights the importance of biosecurity in aquaculture to prevent economic losses and maintain fish health. Research continues to explore more sustainable and effective control measures, particularly as global aquaculture expands.