Lymphoid organs of teleost fish. III. Splenic lymphoid tissue of Rutilus rutilus and Gobio gobio.

The ultrastructure of splenic lymphoid tissue of two teleost fish, Rutilus rutilus and Gobio gobio, constitutes discrete foci around the small arteries and "melano-macrophage" centres. It contains small and medium lymphocytes, lymphoblasts, macrophages and plasma cells. Plasmacytopoiesis and macrophage-lymphocyte clusters have been described and the significance of "melano-macrophage" centres and macrophage-lymphocyte clusters is discussed.