Pereira J.V., Reis J., Magalhães M.F.
The freshwater pearl mussel Margaritifera margaritifera (Bivalvia: Unionida) is one of the most threatened freshwater bivalves worldwide mainly due to the lack of recruitment in natural populations. The life cycle of this species is marked by the production of larvae (glochidia) that attach themselves to the gills of salmonids, where they undergo metamorphosis to the juvenile stage. The main objective of this work was to contribute to the optimization of the captive breeding conditions of M. margaritifera juveniles by comparing the survival and growth rates of individuals raised under different techniques, namely in artificial systems. Juvenile freshwater pearl mussels were obtained through infection of river brown trouts under controlled conditions and subsequently raised in two different systems: part of the juveniles was kept in plastic containers without water circulation (closed system), while artificially fed, and the rest released into natural substrate of an indoor raceway supplied with river water (open flow-through system) and grew without human intervention. Survival and growth rates were monitored during the captivity period, over 3 months, and compared between different systems. Post-parasitic mussels raised in plastic containers showed a gradual decline in survival rate throughout the experimental period, with only 15% of individuals surviving after 3 months, and reaching a maximum shell length of 452,92 (±48,45) µm. It was not possible to assess survival in the flow-through system. In this system, juveniles reached an average length of 561,49 (±69,99) µm, corresponding to an increase in length three times that observed in the closed system. The individuals raised in the flow-through system had a significantly higher growth rate than juveniles in the closed system. In conclusion, the open system was the most cost-efficient, producing a high number of healthy juveniles with little need for human intervention.