Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
He Said, She Said: Gender Confusion in the Big Muddy
Midwest Region, January 27, 2012
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Internal anatomy of shovelnose sturgeon. Male with normal testis (top), normal female ovaries (bottom) and intersex male with ova on testis (right).
Internal anatomy of shovelnose sturgeon. Male with normal testis (top), normal female ovaries (bottom) and intersex male with ova on testis (right). - Photo Credit: USGS-CERC
Anna Clark, Columbia FWCO, performs a necropsy on a shovelnose sturgeon from the Missouri River.
Anna Clark, Columbia FWCO, performs a necropsy on a shovelnose sturgeon from the Missouri River. - Photo Credit: Patty Herman, USFWS

In 2000, research fish biologist Dr. Diana Papoulias from the USGS Columbia Environmental Research Center (CERC) stumbled upon an odd looking shovelnose sturgeon collected from the Missouri River. During dissection, Dr. Papoulias discovered that this particular sturgeon was not a male or female, rather it was both! An intersex fish is one that possesses both male (testis) and female (ovaries) reproductive tissues. This condition has been widely documented in small and largemouth bass, but less is known about intersex in sturgeons. Since her discovery, Dr. Papoulias and others have been working to collect shovelnose sturgeon throughout the Missouri and Mississippi Rivers to determine the prominence of this condition. Intersex in sturgeon has now been found in rivers around the world (usually in highly polluted areas) and in several other sturgeon species including the federally endangered pallid sturgeon. Research since 2000 on the Mississippi and Missouri rivers has found from 7- 23% (more likely near urban areas) of shovelnose caught in these systems to be intersexed, mostly males with female oocytes.

Last year, the Nebraska U.S. Fish and Wildlife Service Ecological Services Field Office (NEFO) proposed a study to determine what effect hormonally active agents (HAAs; endocrine disruptors that interfere with important hormonal processes) and thermal influences have on the incidence of reproductive abnormalities within the native shovelnose sturgeon populations in the Missouri River. This species is often used as a pallid sturgeon proxy, as they are much more common, share a similar life history and have an overlapping range. There is concern that reproductive abnormalities are increasing the pallid sturgeon’s likelihood of extinction. To address this issue, the NEFO has joined with many partners including the Columbia Ecological Services Field Office, Columbia FWCO and Nebraska Game & Parks. The initial stages of this 2-year project began in fall of 2011.

In September and October, Columbia FWCO station technicians targeted shovelnose and captured fish from multiple locations. Since the extent of these abnormalities cannot be detected by sight alone, cellular and molecular techniques are required for a thorough investigation. This necessitated careful documentation and time sensitive processing of tissues harvested for testing and analysis. Temporary laboratories were deployed in the field providing all the capabilities needed to facilitate this type of study. A total of 41 sturgeon were captured, 17 female and 23 males. Macroscopically only a single intersex was found, but histological verification is pending. Fish collection sites were selected in proximity to facilities and outfalls that may contribute HAAs or have thermal effects on the system (waste water treatment plant effluent, wastewater treatment wetland, combined sewer system outfalls and facilities that discharge “cooling waters”). Polar organic chemical integrated samplers (POCIS) and temperature loggers were deployed at locations above and below each site. POCIS samplers are passive means of measuring HAA concentrations in the water. Based on the chemicals stored in the POCIS sampler, researchers can simulate theconditions an aquatic organism may be exposed to over a given amount of time.

Although we do not know the exact cause of development of intersex reproductive organs, researchers think they might have a clue. Contaminants such as organochlorine (OC) pesticides (DDT, Dieldrin, Chlordane, etc.) have been used extensively in the U.S. since the 1940’s. Although most of these harmful chemicals are now banned or restricted in the U.S., they take a long time to break down and are still present in the environment. These and other HAAs can accumulate in river and lake sediments, where bottom feeding fish (i.e. shovelnose and pallid sturgeon) may consume them directly or indirectly. Some OC compounds act similar to natural hormones once they are in the body and can interfere with normal hormonal functions critical for sexual differentiation and development.

While there is no direct link between intersex fish ratios and concentration of HAAs in sediment, recent research has linked HAA exposure during sexual maturation to suppressed reproductive organ development in shovelnose sturgeon. It usually takes this species 2-3 years for reproductive tissue to develop, which means there is a greater chance for build-up of contaminants in their system that could affect sexual development. Determining the rate of these reproductive maladies in Missouri River shovelnose sturgeon will provide valuable insight into the overall health of our waterways and one of the more subtle, yet none the less devastating, impacts of pollution. All of the partners on this project will be working hard in the coming year to learn more about the abundance of intersex sturgeon and factors that may be contributing to this widespread problem.


Hilary Meyer, Jennifer Gorman and Heather Calkins

Contact Info: Heather Calkins, 573-445-5001 ext 29, heather_calkins@fws.gov
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