HEPATOCYTE CLUSTERS IN THE SPLEEN - A NORMAL FEATURE OF SOME POPULATIONS OF BROWN BULLHEADS IN NEW-YORK-STATE

Since 1985, fish pathologists at Cornell University have studied lesio ns in freshwater fish inhabiting natural waters throughout New York St ate in order to clarify possible adverse effects of contaminants on fi sh health. In the course of these studies, we have conducted complete necropsies on over 400 brown bullheads and histologic examinations of the major organs of over 370 of these fish. In the course of our histo logic studies, we observed islands of well-differentiated hepatocytes in the spleens of neoplasm-free brown bullheads from 2 of the 37 diver se lakes, rivers, and ponds that we sampled. The splenic hepatocyte is lands occurred in 11-100% of fish from the 2 affected sites, with 1-50 hepatocyte clusters per section of spleen. Hepatocyte islands measure d up to 1 mm in diameter. Unlike the metastases of hepatocellular carc inomas, which we have described elsewhere in this issue (9), these isl ands of hepatocytes in the spleens of neoplasm-free fish were not evid ent grossly. These hepatocyte clusters in the spleen of certain popula tions of brown bullheads may lead to confusion in studies of neoplasia in brown bullheads. Caution is advised in interpretation of metastasi s of liver neoplasms to the spleen of brown bullheads.