KWRRI Research Reports


The effects of zinc on embryos and larvae of the fathead minnow (Pimephales promelas) were studied using standard 8-day embryo-larval bioassay techniques. The objective was to determine if there was a period in embryonic development which would be the most sensitive to the toxic and teratogenic effects of zinc. Five developmental stages were exposed to 0.5, 1.0 and 3.0 mg/L. After 96 hr, all animals exposed to 3.0 mg Zn/L were dead. The hatching stage was the most affected by 1.0 mg/L, with only 59% surviving after 96 hr, while the tailbud stage showed essentially control-level survival. However, virtually all larvae at all stages were abnormal at 1.0 mg Zn/L, displaying edema and curvature of the vertebral axis. Although LC50 values for the five developmental stages ranged from 0.13 to 0.62 mg/L, there was not a significantly most sensitive stage based upon this criterion. Findings during the posthatch stage proved interesting. When larvae were exposed to 1.0 mg Zn/L only during the 96 hr after hatching, all animals were anomalous. However, if zinc exposure occurred only during the prehatch period and larvae were placed in control water posthatch, only 5% of the larvae were abnormal. These results indicate that at sublethal concentrations perhaps the chorion imparts a protective mechanism to the teratogenic effects of zinc, but that this protection is lost after hatching.

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The work upon which this report is based was supported in part by funds provided by the United States Department of the Interior, Washington, D.C., as authorized by the Water Resources Research Act of 1984. Public Law 98-242.