Scientists Warn: Warming Waters Are Fuelling a Dangerous Salmonid Parasite in Czech Rivers

Researchers from Mendel University (MENDELU) have raised the alarm over the spread of Tetracapsuloides bryosalmonae, a dangerous parasite that infects salmonid fish in Czech rivers. The team surveyed 59 sites along 42 waterways across the country and found the pathogen's DNA in 61.8% of the fish examined, with the parasite itself detected at 78% of the sampled locations.

The parasite needs two hosts to complete its life cycle — salmonid fish and freshwater bryozoans, tiny invertebrates that form colonies on underwater stones, roots or branches. When conditions favour bryozoan growth, the parasite produces infectious spores that are released into the water and go on to infect fish.

How the parasite attacks fish

"The main target is the kidneys, where the parasite multiplies and damages tissue. This leads to swelling of the kidneys and disrupts their normal function. However, fish that survive an infection are able to gradually repair the damaged tissue and build up a certain resistance to reinfection," explained MENDELU expert Miroslava Palíková.

According to the researchers, the disease progresses most aggressively when water temperatures rise above 12°C, making summer and early autumn the riskiest periods. Experts warn that climate change is likely to drive further spread of the infection and more severe outbreaks in the future.

No cure yet — prevention is key

There is currently no reliable treatment for the disease. Experiments have shown that ordinary table salt — sodium chloride — can reduce fish mortality and ease symptoms, but applying such measures in open waterways simply isn't feasible.

That makes prevention all the more important. On fish farms, the most effective solution is to use groundwater or well water, which contains no bryozoans. Preventing infection in the wild is far trickier, but measures such as reducing eutrophication (excess nutrient buildup in water), cooling water using cold reservoir supplies, and maintaining high genetic diversity within fish populations can all help.

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Source: ekolist.cz