Fish Blood
Fish blood, like that of other vertebrates
and many invertebrates, is composed of blood corpuscles (cells) suspended in plasma that is circulated through-out the body tissues. The cells are of two basic types, erythrocytes (red blood cells, RBCs) and leukocytes (white blood cells, WBCs). In this section we will first describe the nature and function of erythrocytes and leukocytes, then briefly describe how these cells are enumerated, and finally discuss in detail the structure and function of hemoglobin, the oxygen-carrying pigment of the blood.
Both RBCs and WBCs are formed from hemocytoblast precursor cells which may originate from a variety of organs but usually mature after they enter the bloodstream. In hagfish the primary blood-forming site is the mesoderm envelope surrounding the gut. Adult lampreys (Lempira) synthesize blood cells from the fatty tissue dorsal to the nerve cord. Elasmobranches fishes produce erythrocytes from the organ of Leyden (situated in the esophagus), special tissue around the gonads, and especially the spleen. Splendid production of RBCs may consist either of immature erythrocytes or of cells which differentiate into erythrocytes after entering the blood. Teleostean hemopoietic (blood-forming) sites are primarily the kidney and spleen. Fish bone has no marrow forhemopoiesis.