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Anomalies observed in the Sexual Development
Summary composed by Jim Waterman - BASIN
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The following page is a summary of research conducted by University Colorado Department of Integrative Physiology research personnel:
Feral white suckers (Catostomus commersoni) were collected on Boulder Creek downstream from wastewater treatment plant (WWTP) effluent and from reference sites. This effluent is known to contain endocrine-active compounds including alkylphenols, bisphenol A, and reproductive steroids. Gonadal intersex and other forms of reproductive disruption were found in white suckers collected downstream of WWTP effluent but not at reference sites. The male to female ratio was skewed toward females at the downstream site.
Abnormalities in gonadal morphology, including smaller ovaries, less developed oocytes, and asynchronous follicular development were noted in female white suckers downstream of the WWTP. Elevated plasma vitellogenin was also reported in downstream juvenile white suckers. The reproductive potential of native fishes may be compromised in stream reaches of western states where large volumes of treated wastewater are discharged into relatively small-sized streams.
A long-lived species, the white sucker
(Catostomus commersoni) was selected as
the target species. White suckers tolerate a
wide variety of conditions including river
stretches greatly enriched from domestic
sewage treatment plant effluents. White
sucker have been collected at sites
immediately downstream of WWTP
effluents in Colorado. Propst (1982) often
found the white sucker to be the most
common fish at such locations, although
numbers were lower than at similar
unpolluted sites. Spring sampling dates
coincide with spawning in white sucker
while fall sampling dates coincide with
reduced stream flows and with male and
female gametogenesis.
The White Sucker is widely distributed throughout North America and is common in Front Range streams. A healthy White Sucker population has been observed in Boulder Creek and this species is commonly observed in the vicinity of WWTP outflows. As the research sought to examine effects of anthropogenic impacts, comparison to a reference site upstream of the City of Boulder WWTP effluent discharge was desired. The white sucker is one of the few species found in Boulder Creek both in the warm water stream segments east of the city and the cold water segments flowing through Boulder Canyon, west of the city.
Boulder Creek was sampled above and below the
effluent of the City of Boulder wastewater treatment
plant (WWTP). Boulder Creek upstream of the
Boulder WWTP flows through the city of Boulder and
receives all storm water runoff from the municipal
area. Pristine comparison sites were not available
within the distributional range of the target species.
Upstream reference sites were downstream of city of
Boulder storm water runoff and upstream of all
WWTP effluent. (
Map of water quality monitoring site on Boulder Creek )
Fish were collected using electro-fishing equipment
with a pulsed DC current in spring and fall of 2003 and 2004. Fishes and sample
tissue were handled in the same manner in the spring and fall. Fishes were
anesthetized with MS222, weighed to the nearest 1 gram and measured for total
length to the nearest mm. Gonads were removed, weighed to the nearest 0.1
gram and preserved in
10% NBF. Relative size and color were noted and any abnormal
development described. Small portions of the head, middle, and caudal sections
of the gonad were embedded in paraffin for histological
analysis. Sections (10mm) were stained using
hematoxylin and eosin (Presnell and
Schreibman 1997). Ovaries were examined
under a light microscope to determine the sex
and reproductive stage of each fish. The
reproductive stage of the ovaries was
determined using a five-stage classification
system modified from Goodbred et al. (1997).
Plasma vitellogenin was assayed with an anticarp
ELISA kit (BioSense) following the
manufacturer’s protocols.
Results
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CU researchers sampled the white sucker populations at reference points and downstream of WWTP outfalls. Approximately equal distributions of male and female were expected and such distributions were found at the reference site. However gender distributions downstream of the WWTP effluent discharge were found to be significantly inconsistent with expectations; with better then 90% female. | |
| While migration of males away from the WWTP discharge area has not been eliminated as a contributing factor, examination of gonadal tissue and vitellogenin proteins support theories that gender distributions are a result of abnormal reproductive tissue development. The few male individuals found at these sites showed significant signs of abnormal development of reproductive tissue | |
Sexual Differentiation
Typically sexual differentiation occurs in white suckers during
the 2nd year of life. Gender development is normally determined
by genetics; however in some species sexual differentiation can be
influenced by environmental factors, particularly "via exogenous
hormonal influences at certain stages of development" (Environmental
Biology of Fishes Malcolm Jobling, 1995, pg 297). | |
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Serum Vitellogenin LevelsAs female fish approach sexual maturity (several months before spawning) the liver begins to produce vitellogenin, a lipophosphoprotein-calcium complex which is released into the bloodstream and transported to the ovaries. This compound forms the basis of future egg yolk protein and stimulates the development of ovarian follicles. While the initiation of vitellogenin production is believed to be tied to increasing photoperiod it is also marked by increased serum estradiol, suggesting environmental hormones may contribute to elevated vitellogenin levels in downstream juveniles. | |
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Follicular Tissue DevelopmentDuring the normal development of follicular tissues 2 distinct stages (possibly simultaneous) are observed, one prior to and a second following onset of vitellogeneous. CU researchers found a much wider variation in follicular development in individuals downstream of the WWTP effluent discharge. | |
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| A characterization of follicular development in ovaries from size-matched (>200mm) females shows that downstream fish possess significantly more simultaneous ovarian follicular stages than reference fish (P<0.01). All upstream fish examined possess only two follicular stages, one pre-vitellogenic and one post-vitellogenic. Downstream fish possess between one and four simultaneous follicular stages. | |
While the duration of this study did not address long term population impacts no white sucker population impacts have been observed. It is possible that migration of viable males into the WWTP reach may maintain relatively strong populations however the documented disruption of the normal development of reproductive tissue would be expected to impact the the reproductive success of individuals and conceivable will eventually impact overall populations.
Acknowledgments CU Research Funding: US EPA Region, 8 NPDES WQCA #CP988934-01 In-kind support from the Colorado Division of Wildlife
