ABSTRACT Sewage pollution is an increasing problem for Perna perna mussel farmers in Brazil, and there is an urgent need to adopt post-harvest treatments, such as depuration, to reduce the associated microbiological risks. However, depuration of this species has been discouraged by experiences showing that the animals usually spawn during this procedure, bringing difficulties for water treatment and making them lighter, weakened, and undesirable to be traded as a live product. This study aimed at developing a protocol to prevent mussels from spawning by modulating the water temperature during depuration. For one year (from 2021-07-07 to 2022-06-29), market-size mussels harvested from the Brazilian southern coast were divided into groups of five and immersed during 50 hours in sets of experimental units (15 L acrylic aquariums) that emulated depuration tanks with different water temperatures (ranging from 8°C to 31°C). During this period, the experimental units were inspected nine times to check for spawning/spawned mussels. Analysis of the overall results showed that 21 (95.5%) out of the 22 assays resulted in mussels spawning and that this behavior was mostly recorded (80.3%) within the first 5:30 hours of the assays. The models developed (binary logistic regression) indicate that conditioning the depuration water to temperatures 5°C lower than those registered at the harvest site holds the potential to reduce the chances of spawning by more than 50%, and these chances drop to 8.2% when this difference reaches 10°C. Further studies are needed to show how reducing water temperature during depuration influences its efficiency in terms of pathogen reduction, aiming to define the best protocol to optimize microbial removal and minimize spawning. Brazil postharvest post treatments risks However procedure lighter weakened product 20210707 2021 07 2021-07-0 20220629, 20220629 2022 06 29 , 2022-06-29) marketsize market size 5 15 (1 aquariums ranging 8C C 8 31°C. 31C 31°C . 31 31°C) period spawningspawned spawned 2 95.5% 955 95 (95.5% 80.3% 803 80 3 (80.3% 530 30 5:3 binary regression 5C 50% 82 8.2 10C 10 10°C reduction 2021070 202 0 2021-07- 2022062 2022-06-29 1 ( 95.5 9 (95.5 80.3 (80.3 53 5: 8. 202107 20 2021-07 202206 2022-06-2 95. (95. 80. (80. 20210 2021-0 20220 2022-06- (95 (80 2021- 2022-06 (9 (8 2022-0 2022-

Abstract The Santa Catarina Island Bay (SCIB) contributes with the largest production of cultivated oysters in Brazil, which is almost entirely based on hatchery produced cultchless oyster spat, whose metamorphosis is induced by an epinephrine solution. A production scale experiment was carried out to analyze the technical feasibility of the spat-on-shell system in SCIB. The experiment was carried out for 47 weeks, involving an internal phase, the larval settlement, and an external phase, encompassing nursery and growth. Nursery periods varied according to the experimental treatments: T3W - 3 weeks; T5W - 5 weeks; and T12W - 12 weeks. T3W and T5W showed lower survival during the two-week period shortly after transfer of the cultch from the nursery to the grow-out phase, likely linked to premature exposure of the spat in the cultch strings to predators such as fish. The 12-week nursery period showed the best results with clusters with a median of 6 animals and 11.4 g of meat per oyster at the end of the experimental period. Future studies could verify whether longer nursery periods or alternative methods to avoid exposure to predators can outperform these results.