A Study on Deformity of Chub Mackerel

Deｆormed chub mackerel (Scomber japonica) were caught at a ratio of about 10 % of a catch in Ise-bay in summer and autumn 1980. 22 deformed fish and 7 fish with a normal shape were investigated with radiographs and histopathological technics. The radiographs demonstrated spinal lordosis and kyphosis with vertebral deformity. Histopathological study on the central nervous system of all deformed fish confirmed massive infiltration of macrophages carring parasitic microorganisms which were comma-shaped, measured 0.7～1.0×0.5 nm in size and unclassifiable, in the third ventricle, fourth ventricle, optic lobe, medulla oblongata and spinal cord. The microorganisms obsearved were a few or absent in the central nervous system of normal-shaped fish. Based on the results, invasion of the unclassifiable microorganisms into the central nervous system was thought to be a cause of spinal deformity of chub mackerel