Recently a possible function of vitamin B12 in the environment of aquatic organisms was discussed in relation to such phenomena as abrupt bloom of “red tide”. In connection with this significant role of the vitamin, more information should be needed about the source from which the organisms can uptake this vitamin.
Existence of the vitamin found by several authors in the alimentary system of aquatic invertebrates as well as phytoplankton has made it inferable that it may be derived either from food for the animals (mainly phytoplankton) or produced by their intestinal microorganisms. With a view to elucidating these points, the little neck clam, Tapes japonica, has been cultivated in artificial sea water in the presence of vitamin B12 labeled with 60Co at various concentrations. The experiments proved that the clam absorbs the vitamin from the environmental water. The measurement of the radioactivity absorbed into different parts of the clam revealed the following.
1) The radioactive vitamin B12 was transferred from the artificial sea water to the clam within six days (Table 1).
2) The level of radioactive vitamin B12 absorbed in the tissues of the clam was higher in the liver and gill than in the foot and gonad. While almost no radioactivity was detected in the intestinal tract (Table 2).
3) Fairly active absorption ability of the clam for this vitamin was suggested from high concentration factor for radioactive vitamin B12 in the tissues of the clam, especially in the liver (Fig. 2).