Anaesthesia and gonad sampling in the European flat oyster ( Ostrea edulis)

Abstract

Controlled reproduction of the European flat oyster requires the development of tools adapted to this species, including a practical anaesthesia and gonad sampling protocol to facilitate sex determination and the verification of gametogenesis. Three replicate groups of 10 oysters (mean weight ± SD: 29.9 ± 8.5 g) were anaesthetised in 5 L containers using magnesium chloride designed either for laboratory (Flucka®) or agricultural (Dead Sea Work®: DSW) use, at two concentrations (50 or 72 g L −1). No significant differences were observed in the percentages of oysters anaesthetised or subsequent oyster mortality with the different anaesthetics or concentrations, but increasing water temperature from 14.9 to 18.8 °C significantly increased the number of oysters anaesthetised after 3 h. Increasing anaesthesia duration from 1 to 22 h significantly increased the percentage of oysters anaesthetised but did not affect subsequent oyster mortality. Gonad sampling of anaesthetised oysters did not increase oyster mortality either. A reliable anaesthesia protocol was, therefore, defined using 50 g L −1 DSW® magnesium chloride for a 2 to 3 h duration. This protocol was validated by monthly anaesthesia and gonad sampling on the same oysters over a three month period, during which a percentage of 95 ± 2% anaesthetised oysters was observed. Compared with controls (oysters that were neither anaesthetised nor sampled), oyster mortality of monthly anaesthetised batches showed no significant increase.