Ultrastructural and ultrahistochemical studies of post-mortem changes and effects of hypoxia in the bony fish heart.

The ultrastructural and ultrahistochemical properties of post-mortem changed and hypoxic heart tissue of Gadus virens, Gadus morhua, and Poecilia reticulata are described. When incubated for 0.5 h at 20 degrees C the cardiac tissue is rich in vacuoles and endocardial blebs. After 1 h of incubation, the myocardial mitochondria contain some amorphous, flocculent densities (50-100 nm), which seem to increase in number and size with advancing incubation time. Furthermore, the mitochondria in heart perfused by a calcium-containing solution for 7 h at hypoxic conditions contain large numbers of highly electron dense annular-granules (35-50 nm). Numerous myocardial mitochondria exclude tannic acid in tissue incubated or perfused for up to 1.5 h, whereas all mitochondria seem permeated by this substance when incubated for 5 h or perfused at hypoxic condition for 7 h. The amount of myocardial glycogen in P. reticulata is greatly reduced in the hypoxic heart compared with the normal heart. The mitochondria and contractile material, however, seem to tolerate oxygen depletion remarkably well. The present results are compared with those reported previously for the post-mortem changes and hypoxic hearts in fishes and mammals.