Influence of watershed land-use on vitellogenin levels in fathead minnows (Pimephales promelas) in Minnesota shallow lakes

Background/Question/Methods

Environmental estrogens (EEs) have emerged as a serious topic of environmental concern; in particular, aquatic ecosystems are especially susceptible to EE. Owing to their detrimental impact on fish reproduction, determining the sources of EEs is important for management of lakes and streams. Vitellogenin (VTG) induction in male fish is commonly used as a biomarker of exposure to EEs. VTG occurs naturally in female fathead minnows and is an egg yolk protein that can be artificially stimulated in males exposed to EEs. The adverse effects of EEs in fish have been well documented, however to date there are few comprehensive studies which correlate VTG levels to land use in lake watersheds. We studied how land use surrounding lakes is related to VTG levels in fathead minnows.  Undeveloped forested areas in northern Minnesota were expected to have lower EEs, and therefore lower VTG levels, than regions in agricultural and urban areas with greater anthropogenic influences. Male fathead minnows (n= 6-10 per lake) were collected from 13 shallow lakes in four ecoregions of Minnesota, encompassing high agriculture, high urban, and forested areas with minimal human impact. Fathead minnow blood plasma was collected and analyzed for VTG using an enzyme-linked immunosorbent assay.

Results/Conclusions

Males collected from the lakes representing the four ecoregions had significantly higher VTG (ca 10x) concentrations than laboratory controls.  Levels of VTG induction were quite variable, but there were no significant differences among ecoregions or land-use types. Although row-crop farming and residential development were expected to provide the strongest induction of VTG levels, there was no trend between regional land use and VTG levels.  High levels of VTG in the undeveloped forested region suggests that direct human activities are not the sole basis for the spread of EEs, and other causes such as atmospheric deposition, natural plant estrogens, or septic tank leakage could elevate VTG levels in male fathead minnows.