The study of the growth of blood cells and hemopoietic organs of claravia catfish ( Clarias gariepius ) grown in the closed loop water systems on the basis of "RANTOP AGRO-5" LLC in the Krasnodar region. Test materials (prolarvae and larvae aged 5, 10, 15, 20 and 25 days of active feeding) were selected in the spring-summer period of 2013-2014. Prolarvae in mesenchyma of forming mesonephros which begins to develop after hatching had primordial precursor cell and blast blood cells between forming vesicles. There took place differentiation of erythropoietic cells: erythroblasts, pronormoblasts and basophilic normoblasts. Accumulation of hemoglobin in erythrocytes indicates that since the first day of hatching, the blood starts to perform transport function - transportation of oxygen. The rudiment of thymus was observed in larvae aged 10 days. This organ generated lymphocytepoietic cells. The central hemopoietic organ - spleen - was originally registered as a mesenchymal rudiment at the age of 10 days. At the age of 25 days, development of the organ stroma is not finished in clarid catfish larvae. Reticular tissues develop actively. Separate lymphoid clumps in the spleen structure have not been found. Melano-macrofagic centres are also unformed. Qualitative analysis of haemopoiesis showed that in spleen there take place development of all types of blood cells: erythropoiesis, granulopoiesis and agranulopoiesis.
