Mass moralities were encountered in Perca fluviatilis from Axwell Park Pond in Northumberland. It was know from a previous study (Afi 1984) that this population has a high incidence of “liver cysts”. At the time of this morality fish had numerous “cysts” in and on the liver. the kidneys. https://www.markbroyard.com/top-super-pet-naturals-busy-butter-calming-peanut-butter-for-cheap-limited-save/