The presence of testicular oocytes (intersex) in male smallmouth bass (Micropterus dolomieu) in the Missisquoi River in Vermont varied over the period of the study and was not related to concentrations of known endocrine disrupting chemicals in the River. Although previous studies have shown linkages between endocrine disrupting chemical exposures and intersex in fish, these results indicate that unidentified stressors may also be associated with the development of intersex in smallmouth bass and are the subject of continued study.
Endocrine disruption is a form of sublethal toxicity in which natural or anthropogenic chemicals, defined as endocrine disruptors, can lead to changes in normal endocrine system function. In laboratory and natural environments, estrogenic endocrine disrupting chemicals (EEDCs) have been reported to interfere with development, reproduction, immunocompetence, and behavior in fish and other organisms.
The presence of testicular oocytes (intersex) in male fish is often used as a biological indicator of exposure to EEDCs and has been documented globally and throughout the United States. For example, previous U.S. Geological Survey (USGS) research has documented intersex in male bass in the Chesapeake Bay Watershed. USGS and U.S. Fish and Wildlife Service (USFWS) scientists also have documented the presence of intersex and other indicators of EEDC exposure in male bass in northeastern USFWS National Wildlife Refuges.
Although intersex has been documented in wild fish, it is often unclear what initiates intersex in a field setting. Scientists took steps to answer this question through a study in the Missisquoi River, which runs through the Missisquoi National Wildlife Refuge in Vermont. This river was selected because of known presence of biological indicators of endocrine disruption in male bass including intersex.
The scientists collected samples four times from September 2012 to June 2014. Smallmouth bass (Micropterus dolomieu) were collected for measurement of biomarkers of endocrine disruption (severity of intersex, plasma vitellogenin concentrations, and the expression of estrogen sensitive genes in liver tissues). In addition, polar organic chemical integrative samplers were deployed and analyzed to identify EEDCs present in the river during the time of fish sampling.
The scientists reported that intersex prevalence and severity in male smallmouth bass decreased over the period of the study from 93 percent to 28 percent. Intersex severity was also reported to be significantly different between late summer and early spring collections. There was generally an absence of known EEDCs detected at the site during the study period. Other measures such as the presence of plasma vitellogenin and liver vitellogenin abundance in males did not indicate exposure to EEDCs at any of the four sample collections.
Although this study did not determine the cause of intersex decline or seasonal variability, the results augment the understanding of intersex prevalence in male smallmouth bass and nudge the science forward regarding the dynamic nature of intersex prevalence in male fish. The absence of known endocrine disruptors in this study indicates that unidentified chemicals or other stressors may be associated with the development of intersex in male smallmouth bass.
The USGS Fishing and Hunting Science Team and the Endocrine Disrupting Compounds in the Chesapeake Bay Watershed Science Team of the USGS Contaminant Biology and Toxic Substances Hydrology combined programs continues to work to identify the factors that initiate intersex and to determine if intersex presence has any demonstrable adverse effects on fish reproduction or results in population declines in a field setting. Multiyear data sets are currently being generated for smallmouth bass at numerous sites within the Chesapeake Bay watershed to address these questions.
The USFWS and the USGS Contaminant Biology and Toxic Substances Hydrology combined programs funded this study.
Below are other science projects associated with this project.
Fishing and Hunting Integrated Science Team
Functional and Molecular Bioassays
Endocrine Active Chemical Screening Tests Optimized to Improve Precision, Accuracy, and Timeliness
Gestodene Affects Fish Reproductive Behavior in Laboratory Exposure Study
Long-Term Study Finds Endocrine Disrupting Chemicals in Urban Waterways
Endocrine Disrupting Chemicals Persist Downstream from the Source
Chemical Combo and Intersex Fish Found at Smallmouth Bass Nesting Sites
Improvements in Wastewater Treatment Reduces Endocrine Disruption in Fish
Endocrine Disrupting Chemicals in the Slick Scum that Covers Stones in Streams
- Overview
The presence of testicular oocytes (intersex) in male smallmouth bass (Micropterus dolomieu) in the Missisquoi River in Vermont varied over the period of the study and was not related to concentrations of known endocrine disrupting chemicals in the River. Although previous studies have shown linkages between endocrine disrupting chemical exposures and intersex in fish, these results indicate that unidentified stressors may also be associated with the development of intersex in smallmouth bass and are the subject of continued study.
Sources/Usage: Public Domain.USGS scientist dissecting a fish to determine possible effects from exposure to endocrine disrupting contaminants. Endocrine disruption is a form of sublethal toxicity in which natural or anthropogenic chemicals, defined as endocrine disruptors, can lead to changes in normal endocrine system function. In laboratory and natural environments, estrogenic endocrine disrupting chemicals (EEDCs) have been reported to interfere with development, reproduction, immunocompetence, and behavior in fish and other organisms.
The presence of testicular oocytes (intersex) in male fish is often used as a biological indicator of exposure to EEDCs and has been documented globally and throughout the United States. For example, previous U.S. Geological Survey (USGS) research has documented intersex in male bass in the Chesapeake Bay Watershed. USGS and U.S. Fish and Wildlife Service (USFWS) scientists also have documented the presence of intersex and other indicators of EEDC exposure in male bass in northeastern USFWS National Wildlife Refuges.
Although intersex has been documented in wild fish, it is often unclear what initiates intersex in a field setting. Scientists took steps to answer this question through a study in the Missisquoi River, which runs through the Missisquoi National Wildlife Refuge in Vermont. This river was selected because of known presence of biological indicators of endocrine disruption in male bass including intersex.
The scientists collected samples four times from September 2012 to June 2014. Smallmouth bass (Micropterus dolomieu) were collected for measurement of biomarkers of endocrine disruption (severity of intersex, plasma vitellogenin concentrations, and the expression of estrogen sensitive genes in liver tissues). In addition, polar organic chemical integrative samplers were deployed and analyzed to identify EEDCs present in the river during the time of fish sampling.
Sources/Usage: Public Domain.Micrograph of testes from male smallmouth bass that contain immature oocytes distinctive of intersex in this species of fish. The scientists reported that intersex prevalence and severity in male smallmouth bass decreased over the period of the study from 93 percent to 28 percent. Intersex severity was also reported to be significantly different between late summer and early spring collections. There was generally an absence of known EEDCs detected at the site during the study period. Other measures such as the presence of plasma vitellogenin and liver vitellogenin abundance in males did not indicate exposure to EEDCs at any of the four sample collections.
Although this study did not determine the cause of intersex decline or seasonal variability, the results augment the understanding of intersex prevalence in male smallmouth bass and nudge the science forward regarding the dynamic nature of intersex prevalence in male fish. The absence of known endocrine disruptors in this study indicates that unidentified chemicals or other stressors may be associated with the development of intersex in male smallmouth bass.
The USGS Fishing and Hunting Science Team and the Endocrine Disrupting Compounds in the Chesapeake Bay Watershed Science Team of the USGS Contaminant Biology and Toxic Substances Hydrology combined programs continues to work to identify the factors that initiate intersex and to determine if intersex presence has any demonstrable adverse effects on fish reproduction or results in population declines in a field setting. Multiyear data sets are currently being generated for smallmouth bass at numerous sites within the Chesapeake Bay watershed to address these questions.
The USFWS and the USGS Contaminant Biology and Toxic Substances Hydrology combined programs funded this study.
- Science
Below are other science projects associated with this project.
Fishing and Hunting Integrated Science Team
The Fishing and Hunting integrated science team focuses on contaminant and pathogen exposures in the environment that could impact the presence and vitality of fish and wildlife populations that drive commercial, recreational and subsistence activities such as hunting and fishing. If actual risks are identified this project will inform how to economically and effectively minimize risk by providing...Functional and Molecular Bioassays
About the Research The Environmental Health Program collaborates with scientists from the Functional and Molecular Bioassay Laboratory to apply and modify microbial and eukaryotic reporter bioassays to detect the presence of bioactive chemicals in environmental water samples. These analyses compliment analytical chemistry and biological datasets. The laboratory adapts and applies cell isolation...Endocrine Active Chemical Screening Tests Optimized to Improve Precision, Accuracy, and Timeliness
Scientists optimized existing endocrine active chemical screening tests to improve their precision, accuracy, and ability to screen more samples in a shorter time-frame. The optimization was done to more rapidly obtain results from the bioassays so that research on the risks of endocrine active chemical exposure can proceed more rapidly.Gestodene Affects Fish Reproductive Behavior in Laboratory Exposure Study
Short-term laboratory exposure of adult fathead minnows to the human contraceptive progestin, gestodene (GES), at environmentally relevant concentrations induced rapid and negative effects on reproductive health and suggests that wild fish may be similarly affected.Long-Term Study Finds Endocrine Disrupting Chemicals in Urban Waterways
U.S. Geological Survey (USGS) scientists determined that endocrine disrupting chemicals (EDCs) were present in wastewater treatment plant (WWTP) effluent, water, and fish tissue in urban waterways in the Great Lakes and upper Mississippi River Regions (Indiana, Illinois, Michigan, Minnesota, and Ohio) during 1999 through 2009.Endocrine Disrupting Chemicals Persist Downstream from the Source
Endocrine disrupting chemicals (EDCs) were transported 2 kilometers downstream of a wastewater treatment plant (WWTP) outfall in a coastal plain stream. EDCs persisted downstream of the outfall with little change in the numbers of EDCs and limited decreases in EDC concentrations.Chemical Combo and Intersex Fish Found at Smallmouth Bass Nesting Sites
Chemical contaminants including herbicides, veterinary pharmaceuticals, and biogenic hormones have been detected at fish nesting sites in the Potomac River watershed where endocrine disruption in smallmouth bass (Micropterus dolomieu) was also observed. Although these contaminants are known to originate from a variety of human and animal-waste sources, results of a recent U.S. Geological Survey...Improvements in Wastewater Treatment Reduces Endocrine Disruption in Fish
A team of scientists from the U.S. Geological Survey (USGS), the University of Colorado, and the City of Boulder, Colorado, demonstrated that improvements to the treatment process at a wastewater treatment facility (WWTF) reduced the level of endocrine disruption in fish exposed to wastewater effluent discharged from the facility. It is difficult to anticipate the effects that upgrading WWTF...Endocrine Disrupting Chemicals in the Slick Scum that Covers Stones in Streams
The slick scum or biofilm that covers most rocks in streams can accumulate contaminants that disrupt reproductive and other endocrine systems in fish. This is the finding of a team of U.S. Geological Survey (USGS) and University of Colorado Boulder scientists as described in a recent article in Environmental Science and Technology (Writer and others, 2011). Biofilms are a mixture of algae... - Publications