Metabolic rate of blue mussels (Mytilus edulis) under varying post-harvest holding conditions

Abstract

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.