The mussel (Mytilus edulis) is successfully grown in aquaculture in
Europe. Mussels are usually sold live and wet storage is becoming more common. In this
study, oxygen demand and ammonia excretion were assessed at increasing water temperatures
and different post-harvest situations. This information was used to calculate minimal flow
rates per unit biomass of live mussels sufficient to keep oxygen above 5 mg L-1
or 50% saturation, and avoid accumulation of ammonia in commercial wet storage. In this
study, rope-grown mussels were kept out of water for 8 h to simulate harvesting conditions
and then re-immersed in holding tanks at 5, 10 and 15 °C. Oxygen and ammonia
concentrations were measured immediately after mussels were re-immersed (0 h), after 6 h
and then every day for 3 days. After this period, the mussels were again kept out of water
for 48 h to simulate long-distance transport and once again re-immersed for the same
period as before. In the first 6 h after re-immersion, the oxygen consumption was between
7.5 and 12.2 μmol g-1 h-1 (dry flesh) and after
this period it decreased to a standard level of around 4.0 ± 0.9 μmol
g-1 h-1 and was independent of temperature. There were no major
differences in oxygen consumption between mussels having spent 8 and 48 h out of water at
any of the subsequent water temperatures used for re-immersion. In contrast, the ammonia
excretion showed greater differences according to temperature and time out of water.
Ammonia excretion was lowest at 5 °C (<0.01 μmol g-1
h-1). The implications of these results for the industry and authorities are
discussed considering the water flow rate, depuration specifications and energy costs.