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

In 1993 very high mortalities of cultured kuruma shrimp, Penaeus japon icus, outbroke in Japan, forcing many shrimp farms to be temporarily c losed. Moribund shrimp exhibited red coloration or discoloration and s mall white spots on the body. Degenerated cells characterized by hyper trophied nuclei, being stained homogeneously with hematoxylin, were ob served in various tissues originated from meso- and ectoderm, such as cuticular epidermis (most frequently), connective tissue, lymphoid org an, antennal gland, hematopoietic tissue and nervous tissue. Hemocytic encapsulations, ranging from 20 to 50 mum in diameter, of necrotic ce lls were also frequently observed in many shrimp examined. No differen ce 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 t he already-known diseases of penaeid shrimp suggested that this is a n ew infectious disease in penaeid shrimp of which etiological agent mig ht be a virus.