Non-sacrificial methodology to sample oyster tissue and monitor Ostrea edulis reproductive state within aquaculture settings

Aquaculture production and restoration often require the sampling of oyster gonad tissues to monitor gametogenesis and reproductive traits, and for biosecurity practices. This is particularly relevant to Ostrea species, the sexes of which cannot be determined based on gametes release during the spawning phase. However, sampling of oyster tissue relies predominantly on destructive methods, which involve the removal of oyster shells and the dissection of tissues for histology. This approach prevents the monitoring of the same individuals over time, leading to approximation of sex ratios and overestimation of oyster reproductive parameters. It also involves the sacrifice of oysters, which is undesirable and prohibitive, particularly for restoration practices and endangered species with limited broodstock availability. The development of efficient and reliable non-invasive techniques is crucial, particularly within commercial and research aquaculture, to enable the selection of breeding and biosecurity screening protocols. The present study compared two non-sacrificial methods, in isolation and in combination with biopsy of oyster gonadal tissue. The effect of shell drilling, a novel non-sacrificial sampling method, and weekly exposure to anaesthesia (MgCl2), was assessed on the European flat oyster Ostrea edulis health and survival, using mortality rates and physiological parameters (growth and clearance rate). Although the combination of anaesthesia and biopsy is currently used in aquaculture and research, the weekly exposure to this method resulted in substantial oyster mortality (25%) and significant reduction in clearance rate (p ≤ 0.012) after 4 weeks of experiment, which indicates a clear physiological stress response to frequent use of this technique. The combination of shell drilling and biopsy, however, resulted in no oyster mortality (0%) and fast shell regeneration (100% in 3 weeks). Therefore, it represents a promising alternative to destructive approaches, which could facilitate future monitoring and manipulation of sex ratios, and genetic and disease screening, without sacrificing remnant depleted stocks.