Effects of simulated transportation stress on viability, water release and ammonia excretion of blue mussels (Mytilus edulis) during dry storage
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- Institutt for marin teknikk 
Norway has a great potential for blue mussel production. However, the blue mussel industry has not yet reached a commercial viability comparable with other mussel producingc ountries. There are still some major challenges associated with production and marketing, included quality problems assumed to arise under transport from the processing units in Norway to the consumers in the European markets. Norway has a relatively long distance to the main markets compared to European competitors, and this implies extended transport time and hence enhances transport stress. This means that to develop profits, the Norwegian blue mussel industry needs to seek solutions to diminish the negative effects of transportation. The objective of the thesis was to reveal the susceptibility of blue mussels to transport stress, including effects on viability and quality-related parameters after prolonged periods of dry storage. Several laboratory experiments were conducted, including commercial-sized mussels and a custom-arranged shaking implement to simulate transport stress. Some high-relevant end-point parameters as filtering capacity, water leakage and ammonia excretion were investigated in order to detect critical effects of shaking stress after aerial expose, simulating truck transport to the markets. The results showed no significant differences in any end-point parameter between the non-stressed and stressed mussels measured, and therefore indicated that the experimental mussels were not affected by shaking. However, no field verification (on board truck) was undertaken and the results therefore may reflect poor simulation power of the experimental setup. In all experiments, the applied method included vibration velocity of 33.1 mm s–1 or 33.1 mm s-2 during 10 minutes, but this may not be fully adequate with regard to real mussel transport. The study revealed that the viability and quality of the mussels were negatively affected by a prolonged dry storage period. After 2 days of dry storage, the mussels still maintained high viability and quality, but both were strongly reduced after 6 and 8 days. However, no individuals died during the experiments. In addition, relationships were found between season and performance of the experimental mussels, and also between feeding aspects and the magnitude of the end-points measured. The data from the present investigations show that the ammonia concentration in water released from the mussels was significantly higher than the concentrations in the material excreted to seawater and in the mantle cavity fluid. A possible explanation may be that the accumulation of nitrogenous metabolic end-products formed when the mussels were exposed to air under anaerobic condition, became microbial degraded to ammonia which eventually was excreted with the released water. However, the ammonia measurements may have been affected by analytical errors, and the results must therefore be treated with caution.