In June 2019, the Ministry of Nature Conservation and Energy gave us permission to collect and keep 33 healthy individuals from the coastal areas of Pula. In addition to everyday monitoring of parameters, the construction of a live food culturing plant for large filtrates was needed. Seeing as the end of 2019 was marked by the mass mortality event of noble pen shells in the Bay of Trieste, and not long after that in Piran’s waters, we were compelled to ask for the Ministry’s permission to isolate individuals from other locations.

Pathogen analysis for Haplosporidium pinnae and Mycobacterium spp. was conducted in the Croatian Veterinary Institute (HVI) for every individual on three tissue samples (mantle, adductor muscle and digestive gland). Analysis was conducted exclusively on dead or sacrificed individuals. To check the condition of noble pen shells in the northern Adriatic, we tested three individuals from three locations (Pula-Stoja, Ližnjan and Peroj). After receiving negative results for H. pinnae and M. sherrisii, we isolated 34 individuals from the location Valovine in Pula on 4 October 2019 and placed them in separate tanks. Unfortunately, after some time, we detected changes in the speed of shell opening and closing and also in the appearance of the mantle. That was when the first individuals in the sanctuary started to die off. Analysis conducted on dead individuals showed that they were infected with M. sherrisii (19 February 2020 and 27 May 2020). To date (25 January 2021), of the 34 viable noble pen shells, only one individual is left alive.

The other three groups came from three different locations: Vinkuran, Štinjan and Rovinj, in February 2020. From each group, one sacrificed individual was tested on arrival. Results of the analysis of H. pinnae and M. sherrisii were negative. Unfortunately, with the increase in sea temperature (in May 2020), significant mortality occurred. We tested three dead individuals. Results showed that all three were infected with H. pinnae, and two also had M. sherrisii present in their tissue. Our opinion and the opinion of the Veterinary Institute is that all of these individuals that arrived at the sanctuary in February 2020 were already infected, but because of lower temperatures, we were not able to detect the presence of the parasite.