Zombie Fungus is Fiction. Saprolegnia is Not.

Fungal infections often bring to mind athlete’s foot or mild skin rashes—minor issues easily treated with over-the-counter ointments. But with the release of  The Last of Us  Season 2, following an already nail-biting first season (click if you dare, spoiler alert and scare warning!) audiences were introduced to a more terrifying vision of fungal infection on an apocalyptic scale. While  Ophiocordyceps unilateralis  does in fact zombify ants, it poses no threat to humans—so no need to prepare for a fungal apocalypse just yet! 

In aquaculture, however, fungal infections are a very real and damaging threat. Unlike in humans, these infections can have serious consequences for fish health and welfare, and the economic impact on farms is significant. Saprolegnia, in particular, is responsible for an estimated $400 million in annual losses to the industry. This cotton-like fungus attacks the skin, fins, and gills of fish, leading to open lesions, secondary infections, respiratory distress, and often high mortality. 

Traditional treatments for Saprolegnia—including formalin, hydrogen peroxide, and other chemicals—come with safety concerns, high costs, and variable effectiveness. Regulatory changes have also removed the only proven option, malachite green, from the toolbox, prompting a push toward preventative strategies and new treatments, including plant-based and biological alternatives. But no single method works universally, which is why innovation is so critical. 

At Onda, we’re focused on helping the industry stay ahead of these growing challenges. Our latest innovation—a controlled Saprolegnia challenge model—provides a reliable way to test new treatments and preventative solutions against this persistent pathogen. In a recent study using this model, we evaluated how stress levels and pathogen load affect young salmon during early life stages. The findings were clear: higher stress and fungal exposure led to significantly higher mortality, especially within the first 10 days. These insights reinforce the need for early intervention and robust hatchery management practices. 

With this model, Onda can support clients from discovery to deployment—helping bring effective, science-backed health solutions to market. Whether you're exploring new products or improving existing protocols, we’re ready to be your partner in protecting fish health and supporting a more sustainable aquaculture industry.