Dangerous CyHV-2 virus in the Oder river and Gliwice Canal – a new threat to crucian carp

On Wednesday, April 23, employees of PGW Wody Polskie in Gliwice collected 670 kg of dead fish from the Oder River between the Koźle and Krapkowice weirs. Tests suggest that the cause of the disaster is the CyHV-2 virus, which primarily affects crucian carp. A few days earlier, a similar phenomenon was observed in the Gliwice Canal.

Dead fish in the Oder

The first alarming reports came from the Gliwice Canal as early as April 13, when employees of Wody Polskie working on the waterway’s Section I recovered 25 kg of dead fish. Two days later, another 50 kg were collected below the Koźle weir on the Oder River. The incident was reported to, among others, the Voivodeship Crisis Management Center of the Opole Voivodeship Office, the Voivodeship Inspectorate of Environmental Protection in Opole, and the Voivodeship Veterinary Inspectorate in Opole.

In the following days, dead fish were observed in Sections I and II of the Gliwice Canal and in the Sławęcice lock chambers. Most of the dead fish were crucian carp, but some carp were also collected from the water. This week, the situation significantly worsened. Dead fish were found throughout Sections 0–VI of the Gliwice Canal — nearly 200 kg were collected on Wednesday alone. An additional 670 kg of silver crucian carp in advanced stages of decomposition were collected from the Oder River itself, specifically from the Koźle, Januszkowice, Krępa, and Krapkowice weirs.

Probable cause of fish mortality: CyHV-2 virus

Employees of PGW WP RZGW in Gliwice, patrolling the Gliwice Canal, also captured live fish and transported them to the National Veterinary Institute in Puławy (PIWet) for testing. PCR tests confirmed the presence of CyHV-2 genetic material in crucian carp tissues. This diagnosis was supported by other characteristic symptoms such as lethargic behavior, necrosis of gill tissue, hemorrhages, and kidney swelling.

In response to the situation, the RZGW in Gliwice decided to intensify water and land patrols in the Oder River basin, the Gliwice Canal, the Kędzierzyn Canal, and multipurpose reservoirs, including the Dzierżno Duże reservoir. Field monitoring is being carried out 24/7 by nearly 200 personnel.

CyHV-2 virus – what is it?

In September 2024, mass fish deaths were reported in Lake Słupeckie, where 30 tons of silver crucian carp were collected. The virus CyHV-2 was detected in their tissues. The pathogen belongs to the herpesvirus family and causes necrosis of the hematopoietic system in common, golden, and silver crucian carp, as well as in some other cyprinid fish, but it is not believed to harm other species. Unfortunately, it is highly virulent, with a mortality rate of 50–100%.

First discovered in Japan in the 1990s, CyHV-2 has been observed in the past three decades in Europe, North America, Oceania, and Asia. In China, between 2011 and 2012, an outbreak among silver crucian carp caused significant economic losses, and mass fish deaths were also recorded in Italy and France between 2012 and 2014.

The pathogen is present throughout Poland as well as in the Czech Republic, Germany, the Netherlands, and Hungary. Its spread northward may be partly due to climate change, but international trade—especially of seemingly healthy fish that are carriers of the virus—also plays a significant role. Epidemics are typically observed when water temperatures range between 15–25°C.

So far, there are no effective treatments or vaccines against the CyHV-2 virus. The only available prevention methods include increased veterinary inspection of imported fish and raising water temperatures in fish farms to above 32°C.

Main photo: Jaroslav Kubec/Wikimedia