Nitrogenous compounds changes in emersed oysters: Crassostrea gigas

The effects of emersing oysters (Crassostrea gigas) for up to 66 h at 4 °C under humid air and nitrogen atmospheres were studied. A significant, gradual body mass loss occurred under nitrogen (8.36 ± 0.85% final weight loss) but no significant loss occurred under humid air (4.92 ± 2.67% final weight loss). Emersion duration and the mantle cavity fluid (MCF) total ammonia (TA) concentration showed a positive, linear relationship (r2 = 0.73 and 0.74 under humid air and N2, respectively). The MCF TA and trimethylamine (TMA) contents were also positively related (r2 = 0.64 and 0.69 under humid air and N2, respectively). e was the most abundant soft tissue free amino acid (71.07 ± 11.8%) in the control group and its concentration did not change significantly under either treatment. The concentration of alanine and valine increased significantly only under humid air. Under N2, the concentrations of valine and lysine increased significantly and aspartate decreased significantly. ate showed a large increase during the first 6 h of emersion under both treatments but significantly more was accumulated in the N2-exposed group (4.2-fold increase and 8.1-fold increase for the humid air- and N2-exposed groups, respectively). The succinate concentration difference remained higher in the N2-treated groups but, in the final 24 h, levels decreased again (quadratic regressions of r2 = 0.97 and 0.95 under humid air and N2, respectively). Although the trend of succinate accumulation was similar under both treatments, the groups held under nitrogen did not gape (whereas those under humid air did). It is concluded that the implications of gaping behaviour on succinate accumulation in the initial hours of emersion have considerable ecological significance for oysters which occupy habitats in which they may become emersed for some hours naturally. Gaping behaviour also has considerable commercial implications because emersion occurs frequently during the marketing of live oysters.