MASS MORTALITIES OF CULTURED KURUMA SHRIMP, PENAEUS-JAPONICUS, IN JAPAN IN 1993 - HISTOPATHOLOGICAL STUDY

In 1993 very high mortalities of cultured kuruma shrimp, Penaeus japonicus, outbroke in Japan, forcing many shrimp farms to be temporarily closed. Moribund shrimp exhibited red coloration or discoloration and small white spots on the body. Degenerated cells characterized by hypertrophied nuclei, being stained homogeneously with hematoxylin, were observed in various tissues originated from meso- and ectoderm, such as cuticular epidermis (most frequently), connective tissue, lymphoid organ, antennal gland, hematopoietic tissue and nervous tissue. Hemocytic encapsulations, ranging from 20 to 50 mum in diameter, of necrotic cells were also frequently observed in many shrimp examined. No difference in histopathological characteristics between spontaneously diseased and experimentally infected shrimp was recognized. Moreover, the same histopathological changes were observed in a kuruma shrimp which was sampled from the imported package from China, sacrificed one day after arrival in Japan. Histopathological comparison of this disease with the already-known diseases of penaeid shrimp suggested that this is a new infectious disease in penaeid shrimp of which etiological agent might be a virus.