Sex steroids in the female zebrafish (Danio rerio)

In Molnbyggen, a leachate-contaminated lake in Sweden, effects on the reproductive system of perch included a decreased frequency of sexually mature female perch, reduced gonadosomatic index and decreased plasma levels of androstenedione and testosterone, but the contaminants responsible for these effects have not yet been identified. A biomarker-directed fractionation approach could be used to narrow the search for the compound(s) responsible for the adverse effects in Molnbyggen female perch. Thus, it is important to develop and test a suitable biomarker, which can be used in this type of approach. We evaluated if decreased concentrations of sex steroids could work as an in vivo end-point in female zebrafish fed an organic extract of bottom sediments from Molnbyggen. The responsiveness of zebrafish to endocrine alteration was evaluated using a positive control substance, cyproterone acetate (CA), which is known to inhibit steroid biosynthesis. After the 21-day exposure period the concentrations of testosterone (T) and estradiol (E2) were successfully determined by HRGC/HRMS in whole-body homogenates of individual fish. Median T concentrations were 1.7 pmol/g fish in controls and were decreased after exposure both to CA (0.55 pmol/g fish) and Molnbyggen sediment extract (1.2-1.3 pmol/g fish). Median E2 concentrations were 5.3 pmol/g fish in controls and were decreased after CA exposure (2.3 pmol/g fish) and after exposure to Molnbyggen sediment extract (4.0-4.5 pmol/g fish). This suggests that sex steroid concentrations in zebrafish are responsive to endocrine alteration and indicates that compounds with endocrine altering potency are present in Molnbyggen sediments.