Gaping restriction as a mechanism to mitigate live transport and re-immersion physiological stress in mussels

Many shellfish species are intentionally taken out of water at different times throughout their farming cycle; especially those sold to live markets. For example, mussels can spend days out of the water after harvest during transport. In this study, we evaluated the potential to enhance recovery in seawater after aerial exposure in the green-lipped mussel, Perna canaliculus . Survival and oxidative stress kinetics were assessed in mussels with no gaping restriction (NGR) versus mussels in which gaping was moderately (MGR) or fully restricted (FGR) during different emersion periods (3, 5 or 7 days (d) after harvest) and their ability to recover in seawater. Results suggested that gaping restriction had a positive effect on re-immersion recovery survival after 3 d of emersion (43 % higher in FGR and 78 % higher in MGR mussels); however, the benefits were time-dependent, as survival decreased after 5 and 7 d of emersion, regardless of gaping restriction treatment. This was reflected in the changes observed in the oxidative stress biomarkers of mussels emersed for 7 d before re-immersion. These mussels appeared unable to compensate for the accumulated damage during emersion and subsequent reoxygenation stress. Damage was apparent as accumulation of protein carbonyls, lipid hydroperoxide and 8-hydroxydeoxyguanosine within one hour of re-immersion in seawater, with all mussels dying within the following ten days. In mussels that recovered after 3 or 5 d of emersion, levels of oxidative damage decreased within 8 h of re-immersion for the NGR and FGR mussels, while the MGR mussels showed no significant reoxygenation damage after 3 d of emersion and recovered faster (i.e., within 4 h) after 5 d of emersion. The antioxidant enzymes showed similar trends in all gaping restriction treatments, and only catalase and glutathione peroxidase activities decreased within ten days after re-immersion. Understanding the changes over time of the mussels' antioxidant capacity and oxidative damage helps explain emersion thresholds for recovery survival. This study presents a promising tool (i.e., gaping restriction) for consideration to enhance the mussels' ability to cope with live transport, and the subsequent reoxygenation stress when mussels are placed back in seawater in live shellfish markets. • Shellfish are exposed to emersion and re-immersion events during farming, in particular post-harvest when destined for live export markets • This study evaluated mussel gaping restriction as a tool to reduce live transport stress and increase survival after re-immersion • Survival and oxidative stress markers kinetics were used to evaluate performance of mussels at different emersion and re-immersion times • Moderate gaping restriction during emersion enhances the mussel's ability to tolerate aerial exposure and their survival upon re-immersion • We identified a threshold for the benefits of gaping restriction, which was explained by the ability to repair physiological damage during hypoxia and re‑oxygenation.