White Suckers in Boulder Creek

Male white sucker from the Museum's Fish Collection (UCM 6706), collected in April 1950. Arrows indicate the right testis. Courtesy of Ashley Bolden and David Norris, Department of Integrative Physiology, University of Colorado.

Boulder Creek is an essential part of the beautiful Boulder landscapes. It provides a rich habitat for local wildlife, and many organisms, including humans, are dependent on the creek's clean water system.

However, a recent study led by Dr. David Norris at the University of Colorado Department of Integrative Physiology and his research team has detected a sign of chemical contamination of downstream Boulder Creek and subsequent reproductive disruption in white suckers (Catostomus commersonii). Museum specimens collected over 50 years ago provided important scientific data for their research.
The appearance of "feminized fishes" below wastewater treatment plants has been reported in several industrialized countries. We examined white suckers in Boulder Creek downstream from the addition of wastewater effluent. We discovered altered sex ratios (more females than males), production of female proteins by males, and the presence of intersex gonads. In this study, intersex means the production of sperm and eggs in the same reproductive organ. Furthermore, we observed contraceptive-like effects in both males and females. These effects are not seen in white suckers living upstream. Therefore, we have attributed these effects to the presence of natural and synthetic estrogenic chemicals present in very small amounts in the creek's wastewater effluent.
We wanted to know if these reproductively abnormal conditions were a new occurrence or were present prior to the development and use of these chemicals over the past 40 years. Fortunately, the University of Colorado Museum of Natural History had white sucker specimens that had been collected from the same places in Boulder Creek 50-100 years ago.
We carefully removed one gonad from each specimen, and examined thin section slides of it under a microscope. There was no evidence of intersex in any of the museum samples, indicating that our observations in the field today are likely due to the relatively recent appearance of estrogenic chemicals in the wastewater. Higher human population density excreting natural hormones, as well as pharmaceuticals and other synthetic estrogens may have contributed to this alarming phenomenon.
This work also highlights the importance of retaining natural history collections in museums that allow us to go back in time to ask scientific questions that could not be answered today without these collections.