Selenium, an essential trace element, may become concentrated in aquatic ecosystems to levels that are toxic to fish. Finley (1985) and Gillespie and Baumann (1986) have shown that selenium in overflow water from coal burning power plant settling basins contributed to a decline in fish populations. The leaching of selenium from the soil into water systems used for irrigation in highly seleniferous areas of the country poses another serious problem. Studies demonstrated that female bluegill sunfish transfer selenium to their progeny. The objective of the study was to determine whether the selenium levels within fathead minnow embryos in a semi-natural ecosystem resulted from direct uptake by the embryos following spawning, from female-to-progeny transferral, or from some combination of these two occurrences.