Microbial analysis of ozone disinfection in a recirculating seawater system.

describes its mixed-sex nature (Fig. 1D). A single pancreatic tumor was identified in a wild-type strain of zebrafish (AB mainline) of greater than one year of age. Externally, the animal had an irregular knobby swelling of the abdomen; internally, a firm, encapsulated white mass was intimately attached to the anterior intestine. The mass was composed of numerous tightly packed clusters, or acini, of well-differentiated pancreatic cells containing variable amounts of secretory granules in the body of the tumor. Mitotic figures were not identified. Small areas of necrosis accompanied by a schirrous reaction (a proliferative fibroblastic response to aggressive carcinomas) were present in some areas of the tumor (Fig. 1E). Less well-differentiated tumor cells accompanied by a moderate schirrous reaction invaded the adjacent mesenteries and extended to the serosal surface where they formed an epithelial border in place of the normal serosal epithelium. Normal pancreatic acini were noted in unaffected mesenteries of the posterior intestine. Seminomas, dysgerminomas, and pancreatic adenocarcinomas are important and deadly tumors of humans and domestic animals. Once strains and specific lineages of zebrafish with naturally occurring tumors are identified, tumorous animal models using zebrafish could be developed. Such laboratory animal models would be useful in the study of the pathogenesis of tumors at both the molecular and organismal level, and would provide an alternate aquatic animal model for tumor research.