Tracing Maternal Transfer of Methylmercury in the Sheepshead Minnow (Cyprinodon variegatus) with an Enriched Mercury Stable Isotope

Maternal transfer of methylmercury (MeHg) to eggs is an important exposure pathway for developing offspring. However, our understanding of this process is limited, particularly in estuarine fish. We conducted a 91-day chronic laboratory exposure of Cyprinodon variegatus to four concentrations of dietary MeHg ranging from 0.04 to 9.90 mu g g(-1) dw. Juvenile fish were fed a preoogenesis MeHg diet for 28 days, after which the diet was switched to a diet enriched with (MeHg)-Hg-199, spanning the period of oogenesis, allowing us to differentiate between mercury stored in female tissues and mercury assimilated from the maternal diet during oogenesis. We found that both maternal body burden and clutch size were strong predictors of egg Hg content. A constant percentage of preoogenesis Hg was transferred to eggs in each treatment. Additionally, preoogenesis Hg and during-oogenesis Hg were transferred proportionally to eggs, suggesting that both female tissues and the maternal diet during oogenesis are significant sources of Hg.