Abstract
The early development of the head kidney,thymus and spleen of Brachymystax lenok between late em-bryo and larval stages was studied by microscopic observation of serial sections.At a water temperature of 10.0–16.2°C,the order of appearance of lymphoid organ primordia was thymus,head kidney and spleen.The pri-mordium of the thymus formed 5 d before hatching and small lymphocytes appeared 1 d before hatching.Nineteen days after hatching,connective tissue and blood capillaries penetrated into the parenchyma of the thymus and the trabeculae appeared.Differentiation into indistinct inner and outer zones occurred after 35 d.The head kidney primordium,which consisted of undifferentiated hemopoietic stem cells,appeared 2 d before hatching.Kidney tubules were formed 3 d after hatching and lymphoid organs after 10 d.Between 35 d and 40 d after hatching,the epithelium of the renal tubules began to degrade and blood sinuses appeared in the head kidney.When the renal tubules had degenerated completely 50 d after hatching,the head kidney was composed principally of lymphoid tissue and a large number of blood sinuses.The spleen primordium appeared 5 d after hatching and the organ be-came lymphoid on the 16th day.Capillaries and blood sinuses were formed in the spleen between 35 d and 50 d.We conclude that the immune organs are differentiated earlier in Brachymystax lenok than in other fishes.Al-though the overall development rate was relatively slow in Brachymystax lenok,the lymphoid tissues developed earlier than in other teleosts.
Published Version
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