SUMMARY The current study was carried out on haemopoietic organs of sixty specimens of fish species of catfish as an example of fresh water fish and mugil fish as an example of salt water fish including liver, spleen and head kidney. The specimens of catfish were collected from Abbasa fish farm at Sharkia governorate while the specimens of mugil fish were collected from World Fish Center farm at Damietta governorate. The specimens were fixed in 10% buffered neutral formalin and Bouin’s fluid and subjected to processing till paraffin sections were obtained & stained histologically and histochemically. The anatomical findings revealed that, the liver of catfish was dark red in color while it was yellow in mugil and comprised the cranial wider part of the abdominal cavity back to pectoral fin. The spleen of catfish was dark red and rounded in shape situated behind the stomach while the mugil’s spleen was dark red and banana shaped or elongated and involved between coils of intestine. The head kidney of catfish and mugil fish comprised the pharyngeal region and was composed of bilateral lobes located anterior to the swim bladder and ventrolateral to the spinal column. The trunk kidney was extended into the trunk region. The histological findings exhibited that, the liver of catfish was covered by thin fibrous connective tissue capsule formed from numerous reticular and collagenic fibers. The capsule was covered externally by a single layer of mesothelial cells while the mugil’s liver was covered by thin fibrous connective tissue capsule of few collagenic and reticular fibers and characterized by thicker capsule than that of catfish. In both fishes the hepatic lobulation was ill distinct, typical portal triads were absent (but mainly were of bile duct with branch of hepatic artery or branch of portal vein) as diads. The hepatocytes in catfish were arranged into plates separated by dilated sinusoids and these plates were radially arranged around the central veins in the form of hepatic cords. The hepatic blood sinusoids were lined by endothelial cells with prominent nuclei. Also, the liver of catfish showed curvilinear and circular arrays of hepatocytes. In catfish, haemopoietic tissue, melano-macrophage centers and hepatopancreas were associated with large branches of portal vein while in mugil the hepatopancreas was absent. The hepatocytes in mugil were arranged as a network, and they were separated by narrow blood sinusoids lined by endothelial cells and associated with Kupffer cells. The splenic capsule of catfish was thick fibrous connective tissue and covered externally by mesothelial cells and the dense trabeculae were extended from the capsule and penetrated the parenchymal tissue branched forming a net-like meshwork of reticulum which contained numerous collagenic and reticular fibers while mugil’s splenic capsule was thin fibrous connective tissue and the trabeculae were absent. The splenic pulp in catfish consisted of white pulp and red pulp. The white pulp composed of two forms: firstly, the diffuse form which was represented by periellipsoidal lymphoid tissue. Secondly, the nodular form which was represented by the presence of lymphoid nodules (splenic corpuscles). In addition, golden yellow to brownish hemosiderin pigments were present. While the red pulp consisted of splenic sinusoids distributed between numerous small vascular ellipsoids, RBCs, lymphocytes, and melano-macrophage centers. The mugil's splenic pulp consisted of white pulp and red pulp. The white pulp was the chief source of lymphocytes (diffuse form) and the red pulp consisted of splenic sinusoids distributed between ellipsoids, RBCs and lymphocytes in addition to hemosiderin pigments and melano-macrophage centers. The white pulp and red pulp were intermingled together without clear separation. The head kidney of catfish clarified that, it had more concentration of haemopoietic tissue than lymphoid tissue and contained RBCs, lymphocytes, macrophages, dilated vascular spaces, hemosiderin pigments, melano-macrophage centers, numerous reticular and collagenic fibers and endocrine elements included heterotopic thyroid follicles. In mugil's head kidney there was more concentration of lymphoid tissue than haemopoietic tissue, RBCs, lymphocytes, melano-macrophage centers, hemosiderin pigments, few collagenic and reticular fibers and endocrine elements included interrenal and chromaffin tissues. The histochemical findings revealed that, in both fish species the liver capsule, splenic capsule and melano-macrophage centers in the head kidney reacted positively to PAS. In both fish species the liver showed faint alcianophilia around blood vessels in the portal area and showed negative Sudan black B reaction. The liver of catfish showed mild positive reaction with Best’s carmine while mugil’s liver showed strong positive reaction with the same stain.