Effects of substrate size and cleaning regime on growth and survival of captive-bred juvenile freshwater pearl mussels, Margaritifera margaritifera (Linnaeus, 1758)

Abstract

This study tested a culture system for rearing Margaritifera margaritifera at the Freshwater Pearl Mussel Ark in Windermere and investigated the effects of substrate size (0.25-1 mm and 1-2 mm) and cleaning regime (weekly and monthly) on survival and growth. At 362 days (12 months) and 758 days (25 months), a total of 1207 and 518 juveniles were reared successfully in the system described here. After 362 days, survival was significantly higher in 1-2 mm substrate treatments cleaned monthly (55 ± 6%) and lowest in 0.25-1 mm substrate cleaned weekly (14 ± 3%). Growth was significantly higher in 1-2 mm substrates cleaned weekly (length = 1.15 ± 0.21 mm) and lowest in 0.25-1 mm substrates cleaned monthly (length = 0.83 ± 0.23 mm). Survival rates in this investigation were comparable to, if not better than, other published studies culturing M. margaritifera of this age. Juveniles from most treatments did not display size-dependent over-winter survival, but a significant correlation was found between shell length and survival in the 0.25-1 mm weekly treatment which was the least suitable treatment. Additionally we examined the effects of flow rate, dissolved oxygen concentration, ammonia concentration and biofilm as factors which may affect growth and survival of juveniles between July - September 2015. These results provide an insight into findings from the initial work and discussion is offered on the challenges for practically applying this method to captive rearing at the Ark in future