The dusky grouper Epinephelus marginatus is a species associated with rocky bottoms that inhabits coastal reefs from shallow water to a depth of 50 m along all Mediterranean coasts. Due to its high economic and gastronomic value, overfishing has reduced dusky grouper populations throughout the Mediterranean Sea.

Since 2011 numerous observations of dead or moribund adult dusky groupers have been detected in several MPAs. This study aimed to detect by means of molecular, histological, and ultrastructural techniques, the causative agent of the anomalous mortality event of wild dusky groupers in Balearic Islands MPAs.

All analysed groupers showed abnormal swimming, mortality and neurological lesions. The undertaken analysis showed that the virus isolates from wild E. marginatus from the Balearic Islands MPAs were closely related to Dicentrarchus labrax and Mullus barbatus strains from Cyprus and Italy.

The authors state that, although vertical transmission from infected spawners has been described as the major route for nodavirus infection, the undertaken study shows that horizontal transmission among sub-clinical fishes after migration or commercial import for aquaculture production could play a major role in the spreading of the disease in MPAs.

The authors underline that further research is needed to elucidate the geographic origin of the reported viral infection, which is essential for the implementation of a suitable surveillance strategy for the reduction of the disease impact in MPAs, and to further preserve wild susceptible populations in the Balearic Islands.

Valencia et al. (2019) Viral encephalopathy and retinopathy (VER) disease in Epinephelus marginatus from the Balearic Islands marine protected areas. Diseases of Aquatic Organisms 135:49-58.