Rapid Shell Formation

from earlier experiments. Similar results were obtained for the freshwater bivalve Anodonta cygnea (Gade et al., 1975). In this animal, acetate and propionate were responsible for over 75 % of total accumulated end products after 30h of anaerobiosis. As volatile fatty acids can be stored in the animal in esterified form, some of the homogenates obtained in the experiments represented in Table 1 were saponified and analysed for volatile components (Kluytmans et al., 1975). In the control groups approx. 6pmol of acetatelg dry wt. was present together with small amounts of other volatile acids, but no increase could be measured in any of the components after 3 days of anoxia. In a recent experiment the distribution of volatile fatty acids in a number of tissues (adductor muscle, gills, foot, mantle, hepatopancreas, and the rest) from groups of both male and female Mytilus edulis was studied after 0, 1 and 3 days of anoxia. The female tissues contained in most cases somewhat higher concentrations of acetate, propionate and butyrate than their male counterparts. Anaerobic incubation increased the content of propionate and to a lesser extent that of acetate in virtually all the tissues investigated, but this rise was especially pronounced in the gills. Although we have no conclusive data at this moment, the high accumulation of propionate in the gills might well be correlated with the excretion of this acid in the sea water confined within the shells, which amounted in this experiment to 2.5prnollg dry wt. after 1 day of anoxic stress and increased to 21 pmollg dry wt. after 3 days of anoxia. In summary, volatile fatty acids form an end product of anaerobic metabolism of bivalves, increasing in importance with increasing time under anoxia. In Mytilus edulis no fatty acid storage in esterified form takes place after 3 days of anoxic stress, but excretion of free volatile fatty acids in this period has been demonstrated.