Abstract:The concentration and distribution of 54Mn in tilapia fish (Tilapiamossambica Poster)penaed prawn (Penaeus peniciltlatus Alcock) and Clams (Arcagranosa Linnus and Cyclina sinensis Gemlin) were studied, and the content of 54Mnin some biochemical matters in the body of these organisms was measured. The resultsshowed that concentration coefficient of 54Mn in the fish, prawn and the two clamswere in the same order of magnitude. After one month of excretion experiment, most of 54Mn in the fish was completly excreted, however, in the prawn and the clamsonly half of 54Mn content were excreted. The shells of two clams had a special abilityin absorption and concentration of 54Mn. The degestive syrtems of all these organismshad highest concentroting and fastest excreting abilities, while their muscles had lowconcentration and slow excretion abilities. The content of 54Mn was highest in thenuclei acid, but lowest in the organic acid.