Effect of sampling procedures, transportation stress and laboratory maintenance on the structure and function of the digestive gland epithelium of the mussel Mytilus galloprovincialis

The digestive glands of four groups of mussels (Mytilus galloprovincialis) were examined under light and electron microscopes. Individuals of the first group were fixed immediately after their extraction from sea-water; those of the second, after having been kept out of water for 2 h; while those of the third and fourth groups, after maintenance in the aquarium for I day and I week, respectively. The digestive gland cells of the mussels kept out of the water for 2 h presented, in many cases, extensive morphological disorganization, expressed mainly by cytoplasmic extrusions into the tubule lumen. In contrast, the mussels kept in the aquarium for I day showed no disintegration phenomena in their digestive cells, but presented a decrease in the height of the tubule epithelium and increased size of the tubule lumen. Similarly, the mussels kept in the aquarium for I week presented cells characterized by increased height compared to those of the mussels of the previous group, as well as a quite inactive epithelium, with no extrusion of cytoplasmic materials into the lumen. The values of the "lysosomal membrane stability" test (LMS), a bioindicator of general stress, were also evaluated. The mussels kept in the aquarium for I day showed decreased LMS values compared to the values for other mussel groups, which indicated that general stress had increased. Results of the present study show that care should be taken in sampling and handling of mussels for use in biomonitoring studies.