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Determining the effects of ammonia on fathead minnow (Pimephales promelas) reproduction
Citation:
Armstrong, B., J. M. LAZORCHAK, C. Murphy, H. Haring, K. M. JENSEN, AND M. E. Smith. Determining the effects of ammonia on fathead minnow (Pimephales promelas) reproduction. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 420:127-133, (2012).
Impact/Purpose:
Three areas of core and applied research will be consequential on development of molecular indicators diagnostic for exposure to specific xenobiotic, natural stressors, and complex mixtures thereof, in freshwater fish and invertebrates. Research is focused on Agency’s long-established aquatic toxicological organism, the fathead minnow (Pimephales promelas). Although numerous molecular biological approaches are exploited, foremost methods leading to development of molecular indicators are assembly and manufacture of DNA microarrays containing transcriptionally relevant gene sequences of fathead minnow, and the detection of novel or differentially expressed proteins by means of 2-D polyacrylamide gel electrophoresis followed by mass spectrometry. An extensive effort in 'gene discovery' research with the fathead minnow has been the primary emphasis of respective research areas, since high-throughput genome sequencing efforts-such as those in human and mouse-have not been directed toward organisms used in aquatic toxicity testing such as fathead minnows. Gene discovery research is fundamental to identified research areas, and is expected to be augmented by high-throughput cDNA sequencing data arising through a collaborative effort with the Dept. of Energy, Joint Genome Institute. Also, proteins induced to differential expression by chemical exposure will be used in ‘reverse genetics’ approach wherein knowledge of protein sequence will make possible the investigation of gene function and associated mechanistic biology. Following development and validation, fathead minnow microarrays, along with critical indicators identified by expression proteomics, will enable extensive molecular profiling studies, the hypotheses of which are that unique patterns of gene expression will be detected in targeted tissues of fathead minnows exposed to individual chemical stressors. Identification of unique, differentially expressed genes will then provide the basis for stressor-specific, quantitative molecular indicators, theory and methods that can be readily transferred to investigators within USEPA Regions, Tribes and states. Ultimately, proposed research will provide environmental science and risk assessment communities with advanced molecular biological indicator methods, complete with validation studies and guidance for their application.
Description:
Aquatic organisms are exposed to a multitude of contaminants and to fully understand the impact of multiple stressors on fish populations, we should first understand the mechanism of action for each toxicant and how the combined effects manifest at the level of the individual. Ammonia has been known to cause adverse reproductive and mortality effects in individual fish through effects or damage to the central nervous system. A flow-through diluter system was used to test the individual effects of environmentally relevant concentrations of ammonia on fathead minnow reproduction during a 20-day exposure. This data was to be used as a pilot investigation for a future study looking at multiple stressor effects of two contaminants, ammonia and an endocrine disrupting contaminant, on fathead minnow reproduction. All three concentrations of ammonia tested in this study significantly reduced the fecundity after 20 days of exposure. The lowest unionized ammonia concentration tested during this study resulted in a 29% decrease in cumulative fecundity. Therefore, the no effect concentration of un-ionized ammonia on fathead minnow reproduction is estimated to be 0.03 mg/L. Significant findings from this study suggest that U.S. EPA water quality criterion for ammonia in waters where non-salmonids are present is above the lowest observable effect concentration for fathead minnow reproduction. This study demonstrated the importance of revisiting the current U.S. EPA water quality criteria using data derived from more current research.
