First case of betanodavirus infection in a grouper confirmed in Catalonia in 2025

On 7 September a specimen of grouper (Epinephelus marginatus) was detected in waters near Barcelona with clear symptoms consistent with betanodavirus infection, also known as viral nervous necrosis (VNN). The discovery was made possible thanks to a report from a member of the Barcelona Underwater Fishing Association (APS), who sent the specimen to the Fish Pathology Diagnostic Service at the Universitat Autònoma de Barcelona (UAB). Samples of the fish were then sent to the European reference laboratory for this disease, where molecular techniques (qPCR) confirmed a very high presence of the virus in the animal's brain.

This identification, together with other reports of dead or symptomatic groupers, unequivocally confirms the spread of VNN and its presence in the coastal waters of Catalonia. For several years now, this betanodavirus has been causing outbreaks of mortality in groupers and other fish species throughout the Mediterranean, with particularly severe outbreaks in Greece, southern Italy, Spain, and recently in the Azores. In Spain, this virus had already caused outbreaks in the Balearic Islands, and a few years ago outbreaks were detected on the coast of the peninsula, with a progressive advance northwards causing very significant mortality of groupers in nature reserves such as Cabrera and Columbretes.

The UAB and the ICM-CSIC set up an alert and sample collection network

Given this scenario and the risk of spread and new outbreaks posed by the confirmed presence of cases of this disease, particularly aggravated by the abnormal temperatures detected since the end of summer in the seawater off the coast of Catalonia, the UAB and the Institute of Marine Sciences (ICM-CSIC) have set up a permanent alert and sample collection network to quickly identify cases and monitor the evolution of this disease.

Francesc Padrós and Maria Constenla, researchers at the UAB who are also responsible for monitoring, emphasise that "the identification and monitoring of outbreaks and the characterisation of the virus are critical to establishing containment plans, especially in highly sensitive areas with a high density of specimens. The existence of highly accurate diagnostic tools and the availability of a commercial vaccine developed by HIPRA to prevent the disease in farmed sea bass are two great opportunities to implement emergency measures, even if only experimentally and at least in areas critical for this species."

“This case demonstrates the importance of maintaining an active network of observers, such as divers or recreational fishermen, who can detect potential outbreaks at a very early stage”, points out Valerio Sbragaglia, researcher at ICM-CSIC and one of the people responsible for monitoring.

Citizen collaboration and the response of authorities are key to monitoring the health of fish populations and being prepared to respond quickly to possible outbreaks threatening marine biodiversity. In this regard, the researchers are grateful for the sensitivity and interest shown so far by associations such as the APS and the Federació Catalana d'Activitats Subaquàtiques (FECDAS), as well as the managers and technicians of the Cap de Creus Natural Park and the Montgrí, Medes Islands, and Baix Ter Natural Park.