Metabolism and DNA-binding in vivo of aflatoxin B1 in medaka (Oryzias latipes)

1. The medaka (Oryzias latipes), a small aquarium fish, was shown to possess the capacity to rapidly activate AFB1 in vivo at 25 degrees C to intermediates that bind to DNA. 2. The dose-response for in vivo AFB1-DNA binding was linear over the range 70-550 micrograms AFB1/kg body weight. 3. Maximum binding occurred within the first 24 hr after i.p. injection of [3H]AFB1, followed by a rapid loss of adducts. 4. Aflatoxicol (AFL) and unreacted AFB1 were found by HPLC analysis to be the major products excreted into water after AFB1 exposure, with excretion of AFL as early as 2 min after AFB1 injection. 5. These studies show that medaka possess enzymatic systems similar to rainbow trout (Salmo gairdneri) for biotransformation of AFB1 to the epoxide and to other phase I and phase II metabolites.