April 15, 2019 — Extreme weather events and changing ocean conditions are creating unpredictable outcomes for aquaculture. One area where research is offering some insight into what to expect, though, is the increasing incidences of disease.
Anyone who was in France in the summer of 2018 can attest to the searing temperatures that swept the country. From north to south, the nation experienced the second hottest summer since records began. Whilst children played in lakes and the sea to cool off, the shellfish producers of Étang de Thau could only watch as their oysters and mussels perished at the hands of malaïgue – a period of sustained high temperatures and little wind.
The ocean has always been a highly dynamic environment, with its ever-changing conditions presenting challenges to aquaculturalists. However, thanks to human-induced climate change and continuing carbon emissions, events like malaïgue may become more regular occurrences, bringing with them new disease-related challenges.
As every aquaculturalist knows, temperature plays a major role in the growth and health of aquatic species. Certainly, higher temperatures are typically related to higher energetic requirements and demand for food. In an interesting twist, finfish can find their hunger suppressed when held at the upper end of their thermal tolerance for too long – even though their metabolic demands continue to rise. Malnourished fish make for unhealthy fish, which makes for a more stressed and susceptible animal.
Temperature doesn’t just impact farmed animals. As work from Dr Tommy Leung, a parasitologist at the University of New England in Australia has shown, temperature also appears to have a relationship with the severity and duration of disease outbreaks. “If you are in a more temperate region, you might have an outbreak where half of your stock die whereas in the tropics you have over 90 percent dying,” Leung explained. To compound the problem, outbreaks in those warmer tropical and near-tropical regions also happen over a much shorter period. “This means you could have less time to respond to any potential outbreak.”