Percentage survival with SD compared to previous date of hatchery produced O. edulis from two broodstock origins (pre-screened Bonamia free = RvY and Bonamia naïve = NIOZ) in 2020 (A) and 2021 (B). From February until August 2020 the two groups were kept in the harbour of Yerseke (Oosterschelde) in one basket each. From August onwards 1 to 7 baskets per group with two compartments each were placed in Lake Grevelingen. * = significant difference between the two groups, P < 0.05.