A new study finds that while common carp are highly vulnerable to a devastating virus, their close relatives help stop its spread—offering hope for fish farmers and freshwater ecosystems.
For many Israeli families, no Rosh Hashanah table is complete without carp. Whether served as traditional gefilte fish or another festive dish, the fish has long symbolized abundance and prosperity for the year ahead.
But for carp farmers around the world, the holiday favourite has a serious enemy.
Koi herpesvirus (CyHV-3) is one of the most destructive diseases in carp aquaculture, capable of wiping out entire populations in just days. Every outbreak can mean enormous economic losses and lasting damage to wild fish populations.
Now, just in time for the Jewish New Year, researchers from the Hebrew University of Jerusalem and Michigan State University have discovered an unexpected piece of good news: while common carp are highly vulnerable to the virus, several of their closest relatives are surprisingly good at stopping it in its tracks.
Their study found that goldfish, grass carp, silver carp and black carp rarely become infected naturally. Even when scientists deliberately infected them, these fish fought off the virus quickly and were far less likely to pass it on to others.
“Because these fish often live alongside common carp in ponds and lakes, there has been concern that they might act as silent carriers of the virus,” said Prof Lior David of the Hebrew University of Jerusalem, senior author of the study. “Our results show that, although they can occasionally become infected, they are actually very poor at spreading the disease.”
To find out, the researchers recreated how infections occur in the real world. Healthy fish were placed in tanks with infected common carp. While the virus spread rapidly among common carp, only a small fraction of the other carp species became infected, and almost none became ill.
The team then took the experiment one step further, injecting the virus directly into the fish to bypass their natural defences. Even then, the differences remained striking. Unlike common carp, which developed severe disease, the other species rapidly cleared the virus from their bodies and showed little sign of illness.
Finally, the researchers asked the most important question: could these healthy-looking fish spread the virus back to common carp?
The answer was yes—but only inefficiently.
Compared with infected common carp, the other species transmitted the virus much less effectively, making them what scientists describe as “inefficient carrier hosts.” In other words, they are unlikely to drive major disease outbreaks.
That matters because common carp, grass carp and silver carp remain among the world’s most important farmed fish, supplying food to billions of people and supporting aquaculture industries across Asia, Europe, and the Middle East.
“The biggest risk still comes from infected common carp themselves,” David said. “Our findings suggest that the presence of these other carp species is unlikely to be the main cause of disease outbreaks.”
As families gather around holiday tables this Rosh Hashanah, the research offers a timely reminder that protecting one of the world’s oldest farmed fish depends not only on understanding the virus—but also on understanding how some of its closest relatives have learned to resist it.
Media Contacts
Lior David, Hebrew University-RH Smith Faculty of agriculture, Food and Environment
Email: lior.david@mail.huji.ac.il
Research Paper
Dorfman, B., Lamichhane, S., Marcos-Hadad, E., Gorgoglione, B., & David, L. (2026). Differences in CyHV-3 infection and infectivity among common carp and Asian carp species. Aquaculture, 625, Article 744303.
DOI: https://doi.org/10.1016/j.aquaculture.2026.744303
Authors:
Batya Dorfman, Santosh Lamichhane, Evgenia Marcos-Hadad, Bartolomeo Gorgoglione, Lior David
Affiliations:
- Department of Animal Sciences, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
- Fish Pathobiology and Immunology Laboratory, Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA.
- Department of Fisheries and Wildlife, College of Agriculture and Natural Resources, Michigan State University, East Lansing, MI 48824, USA.