114 ILAR Journal

During the past decade, the zebrafi sh has emerged as a lead-ing model for mechanistic cancer research because of its so-phisticated genetic and genomic resources, its tractability for tissue targeting of transgene expression, its effi ciency for forward genetic approaches to cancer model development, and its cost effectiveness for enhancer and suppressor screens once a cancer model is established. However, in con-trast with other laboratory animal species widely used as cancer models, much basic cancer biology information is lacking in zebrafi sh. As yet, data are not published regarding dietary infl uences on neoplasm incidences in zebrafi sh. Lit-tle information is available regarding spontaneous tumor in-cidences or histologic types in wild-type lines of zebrafi sh. So far, a comprehensive database documenting the full spec-trum of neoplasia in various organ systems and tissues is not available for zebrafi sh as it is for other intensely studied lab-oratory animal species. This article confi rms that, as in other species, diet and husbandry can profoundly infl uence tumor incidences and histologic spectra in zebrafi sh. We show that in many laboratory colonies wild-type lines of zebrafi sh ex-hibit elevated neoplasm incidences and neoplasm-associated lesions such as heptocyte megalocytosis. We present experi-mental evidence showing that certain diet and water man-agement regimens can result in high incidences of neoplasia and neoplasm-associated lesions. We document the wide ar-ray of benign and malignant neoplasms affecting nearly ev-ery organ, tissue, and cell type in zebrafi sh, in some cases as a spontaneous aging change, and in other cases due to car-cinogen treatment or genetic manipulation. Key Words: Danio rerio; diet; hepatocyte megalocytosis; husbandry; naturally occurring carcinogen; neoplasia; non-protocol-induced variation; zebrafi s