Individual Level Indicators: Reproductive Function in Estuarine Fishes

EPA Grant Number: R829458C005
Subproject: this is subproject number 005 , established and managed by the Center Director under grant R829458
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: EAGLES - Consortium for Estuarine Ecoindicator Research for the Gulf of Mexico
Center Director: Brouwer, Marius
Title: Individual Level Indicators: Reproductive Function in Estuarine Fishes
Investigators: Thomas, Peter , Rose, Kenneth A. , Cheek, Ann , Nunez, Scott
Institution: University of Southern Mississippi
Current Institution: The University of Texas at Austin , University of Southern Mississippi
EPA Project Officer: Packard, Benjamin H
Project Period: December 1, 2001 through November 30, 2005 (Extended to May 20, 2007)
RFA: Environmental Indicators in the Estuarine Environment Research Program (2000) RFA Text |  Recipients Lists
Research Category: Water , Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration


The overall objective of this research project is to evaluate biomarkers of reproductive function in two estuarine fish species, Atlantic croaker and Fundulus grandis, as early warning indicators of fish population hazards due to the degradation of estuarine environments. One focus of the CEER-GOM program is to investigate the effects of hypoxia, which often occurs in estuaries along the Gulf of Mexico. Currently, little is known about the effects of exposure to moderate hypoxia on reproductive and endocrine functions in estuarine fishes.

One objective of Year 1 of the project was to determine whether reproductive function was impaired in croaker chronically exposed to low dissolved oxygen (DO) levels in a controlled laboratory study. A low DO exposure system was designed that maintained DO levels at 2.5 ppm and 3.5 ppm, 35 percent and 50 percent of normoxic levels, respectively, as well as maintaining water quality. Gonadal growth in males, but not in females, was significantly impaired in croaker exposed to 2.5 ppm for 6 weeks. After 10 weeks of exposure, sperm motility and plasma androgen levels were significantly decreased in males exposed to both of the low DO treatments. An initial spawning trial suggested that fertilization success also is impaired after chronic exposure to low DO. Overall, the patterns of reproductive and endocrine disturbances after exposure to low DO appeared to differ from those typically observed in fish exposed to other environmental stressors such as pollutants. These findings suggest that the mechanisms of reproductive interference by low DO may be specific to this stressor.

Another objective for Year 1 was to develop additional indicators for subsequent evaluation in field studies during the remainder of the project. The genes for two key steroidogenic enzymes involved in gonadal development at puberty, aromatase (estrogen synthesis) and 11ß-hydroxylase (androgen synthesis), have been cloned and almost completely sequenced. Other indicators in croaker and F. grandis have undergone further development and initial evaluation in preliminary field studies in Corpus Christi Bay (CCB), Galveston Bay, TX, and Terrebonne Bay, LA. Site differences in several reproductive indicators such as gonadal growth were observed in both species, which were associated with moderate environmental degradation due to low DO or chemical contamination. These initial field trials suggest that some of the reproductive endpoints selected are potentially useful as individual-level indicators of fish population hazards, whereas others appear less promising. In conclusion, no major problems were encountered and all of the major objectives proposed for Year 1 of the project were accomplished.

Publications and Presentations:

Publications have been submitted on this subproject: View all 24 publications for this subprojectView all 171 publications for this center

Journal Articles:

Journal Articles have been submitted on this subproject: View all 4 journal articles for this subprojectView all 48 journal articles for this center

Supplemental Keywords:

dissolved oxygen, DO, polymerase chain reaction, PCR, Corpus Christi Bay, CCB, rapid amplification of cDNA ends, RACE, population, community, ecosystem, watersheds, estuary, Gulf of Mexico, nutrients, hypoxia, innovative technology, ecoindicators, biomarkers, water quality, remote sensing, geographic information system, GIS, integrated assessment, risk assessment, fisheries, conservation, restoration., RFA, Health, Scientific Discipline, Geographic Area, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Ecosystem/Assessment/Indicators, Endocrine Disruptors - Environmental Exposure & Risk, Aquatic Ecosystem, endocrine disruptors, Aquatic Ecosystems, Environmental Monitoring, Ecological Monitoring, Ecology and Ecosystems, Biology, Endocrine Disruptors - Human Health, Gulf of Mexico, Ecological Indicators, monitoring, ecoindicator, ecological exposure, molecular ecology, estuaries, estuarine integrity, ecosystem assessment, biomarkers, fish, endocrine disrupting chemicals, ecological assessment, estuarine ecoindicator, fish reproduction, animal models, environmental indicators, environmental stress, reproductive processes, water quality, nutrient fluxes

Progress and Final Reports:

  • 2002 Progress Report
  • 2003 Progress Report
  • 2004 Progress Report
  • 2005 Progress Report
  • 2006
  • Final

  • Main Center Abstract and Reports:

    R829458    EAGLES - Consortium for Estuarine Ecoindicator Research for the Gulf of Mexico

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R829458C001 Remote Sensing of Water Quality
    R829458C002 Microbial Biofilms as Indicators of Estuarine Ecosystem Condition
    R829458C003 Individual Level Indicators: Molecular Indicators of Dissolved Oxygen Stress in Crustaceans
    R829458C004 Data Management and Analysis
    R829458C005 Individual Level Indicators: Reproductive Function in Estuarine Fishes
    R829458C006 Collaborative Efforts Between CEER-GOM and U.S. Environmental Protection Agency (EPA)-Gulf Ecology Division (GED)
    R829458C007 GIS and Terrestrial Remote Sensing
    R829458C008 Macrobenthic Process Indicators of Estuarine Condition for the Northern Gulf of Mexico
    R829458C009 Modeling and Integration