The levels of mercury and selenium in twenty -eight gonad specimens of two species of tunas , i.e., sixteen individuals of yellow fin Thuunus albacares and twelve individuals of albacore Thunnus alalunga, are presented . Total mercury content (T-Hg) correlated significantly between gonad and muscle , and T-Hg in gonad was about 30% of that in the muscle. The ratio of methyl mercury content (MeHg) to T-Hg in gonad was small compared with that in the muscle . Selenium content (Se) was relatively

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... igh , and Se in yellow fin was significantly high compared with that in albacore. Moreover , in both the species, Se in the ovary was significantly high compared with that in the testis. The molar ratio (Se/Hg) of Se to T-Hg correlated negatively with T-Hg, and tended to get nearer to 1 with the increase in T-Hg.