Technical Report

Evaluation of the Rio Grande Silvery Minnow Health in Relation to Changes in Water Quality, Pathogens and Other Environmental Stressors (Fish Pathogen Assessment Section)

URL: https://webapps.usgs.gov/mrgescp/documents/Woodland_2009_Evaluation-of-the-RGSM-Health-in-relation-to-changes-in-water-quality-pathogens-and-other-environmental-stressors.pdf

Date: 2009/05/12

Author(s): Woodland J.

Publication: U.S. Fish and Wildlife Service Report, 15 p.

Abstract:

Assessment of pathogens affecting the Rio Grande silvery minnow Hybognathus amarus is crucial in understanding impacts to recovery efforts of this federally listed endangered fish. Viral, bacterial and parasite pathogen examinations were conducted on Rio Grande silvery minnow in this study to provide a comprehensive pathogen assessment. The prevalence of isolated pathogens was determined from up to 60 fish for bacteriology and virology and up to 30 fish for parasitology from each sampling. Collections occurred quarterly at six sites along the middle section of the Rio Grande between July 2006 and July 2008. The top four most prevalent parasites observed were from the family Trichodinidae and the genera Apiosoma, Cryptobia, and Ichthyobodo. No significant bacteria or viruses targeted nationally by the U.S. Fish and Wildlife Service were isolated. There were also no significant overall differences in the mean parasite prevalence between the sites. Correlations between types of infection indicate a majority of ‘parasite only’ infections (65%) compared to ‘bacteria only’ (19%) or ‘parasites and bacteria’ present (16%). The parasites observed in this study range from being normal ectocommensals to possessing potential for acute pathogenesis and are generally indicators of poor water quality. Longer term study and standardization of parasite examination protocols will provide additional information on occurrence trends and potential impacts of the parasites observed. Results of this study provide a baseline of information on the types of pathogens currently observed with Rio Grande silvery minnow in the middle reach of the Rio Grande.