Scientists determined the risk factors associated with smallmouth bass melanistic skin lesions on smallmouth bass in the Susquehanna and Potomac Rivers, in the Chesapeake Bay watershed. A new virus, which appears to be a member of an emerging viral family, the Adomaviridae, was identified in the lesions. Questions remain about the full characterization of the virus and the role of environmental factors, such as temperature and chemical contaminants, in initiation, progression, and health effects of the lesions.
Smallmouth bass (Micropterus dolomieu) are important game fish and a top predator species in the Susquehanna and Potomac Rivers. Smallmouth bass disease and population declines in portions of the Susquehanna and Potomac River watersheds have raised concern among the fishing public and resource managers about the long-term sustainability of fish populations. In addition, visible skin lesions have been observed, including black areas of skin discoloration called melanistic hyperpigmentation or “blotchy bass syndrome.” Although the melanistic lesions have been recognized for many years, the causative factors are currently unknown.
The U.S. Geological Survey (USGS) collaborated with the Pennsylvania Fish & Boat Commission, Pennsylvania Sea Grant College program, and State management agencies, to answer questions about the melanistic hyperpigmentation observed in smallmouth bass. Between 2012 and 2018, scientists used a combination of routine fish population surveys, fish health monitoring surveys, tissue collections, and genetic and microscopic analyses to better understand the prevalence, mechanisms of development, and potential risk factors associated with melanistic lesions in smallmouth bass.
The prevalence of melanistic lesions varied among sites from 3 to 13 percent of the fish collected depending on the year and site. As part of routine population surveys, the prevalence of melanistic lesions in the main stem of the Susquehanna River was greater than in a tributary, the Juniata River. Additional fish were collected as part of ongoing fish health monitoring surveys, which indicated the prevalence of melanistic lesions in smallmouth bass in the Susquehanna River and tributaries was greater than in the Potomac River and tributaries.
Sections of normal skin and melanistic lesions from smallmouth bass were preserved for microscopic and molecular analyses. USGS scientists examined the lesions microscopically and determined that the lesions were noncancerous and that the melanocytes normally present in the dermis had proliferated and (or) migrated to the epidermis.
The Pennsylvania Sea Grant College Program funded the sequencing of 16 normal skin samples and 16 melanistic lesion samples to develop a partial transcriptome—the ribonucleic acid (RNA) instructions inside a cell. The abundance of 55 genes associated with contaminant exposure, melanogenesis, immune response, and a unique viral helicase-like gene were measured. Eleven of 55 genes analyzed were differentially expressed between melanistic and normal skin tissues. Three of those were unique gene sequences, two of which were unidentified and one was a viral gene. The viral gene was detected in 12 of the 16 melanistic areas and in no normal skin samples. The viral gene sequence indicated a similarity to a newly recognized viral family, Adomaviridae, that has been associated with disease in other fish species.
Further research is underway to fully characterize the virus and understand the mechanisms involved in the formation of melanistic lesions and to determine the role of environmental factors, such as temperature and chemical contaminants, in initiation and progression of the lesion.
This research was funded by the Pennsylvania Fish & Boat Commission, the Pennsylvania Sea Grant College Program, and the USGS Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) of the Ecosystems Mission Area, and the Environments and Fisheries Program.
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Below are publications associated with this research.
Hyperpigmented melanistic skin lesions of smallmouth bass Micropterus dolomieu from the Chesapeake Bay watershed
- Overview
Scientists determined the risk factors associated with smallmouth bass melanistic skin lesions on smallmouth bass in the Susquehanna and Potomac Rivers, in the Chesapeake Bay watershed. A new virus, which appears to be a member of an emerging viral family, the Adomaviridae, was identified in the lesions. Questions remain about the full characterization of the virus and the role of environmental factors, such as temperature and chemical contaminants, in initiation, progression, and health effects of the lesions.
Smallmouth bass (Micropterus dolomieu) are important game fish and a top predator species in the Susquehanna and Potomac Rivers. Smallmouth bass disease and population declines in portions of the Susquehanna and Potomac River watersheds have raised concern among the fishing public and resource managers about the long-term sustainability of fish populations. In addition, visible skin lesions have been observed, including black areas of skin discoloration called melanistic hyperpigmentation or “blotchy bass syndrome.” Although the melanistic lesions have been recognized for many years, the causative factors are currently unknown.
Smallmouth bass skin with melanistic lesions. The U.S. Geological Survey (USGS) collaborated with the Pennsylvania Fish & Boat Commission, Pennsylvania Sea Grant College program, and State management agencies, to answer questions about the melanistic hyperpigmentation observed in smallmouth bass. Between 2012 and 2018, scientists used a combination of routine fish population surveys, fish health monitoring surveys, tissue collections, and genetic and microscopic analyses to better understand the prevalence, mechanisms of development, and potential risk factors associated with melanistic lesions in smallmouth bass.
The prevalence of melanistic lesions varied among sites from 3 to 13 percent of the fish collected depending on the year and site. As part of routine population surveys, the prevalence of melanistic lesions in the main stem of the Susquehanna River was greater than in a tributary, the Juniata River. Additional fish were collected as part of ongoing fish health monitoring surveys, which indicated the prevalence of melanistic lesions in smallmouth bass in the Susquehanna River and tributaries was greater than in the Potomac River and tributaries.
Sections of normal skin and melanistic lesions from smallmouth bass were preserved for microscopic and molecular analyses. USGS scientists examined the lesions microscopically and determined that the lesions were noncancerous and that the melanocytes normally present in the dermis had proliferated and (or) migrated to the epidermis.
A hyperpigmented melanistic skin lesion in a Smallmouth bass from the Chesapeake Bay Watershed. The Pennsylvania Sea Grant College Program funded the sequencing of 16 normal skin samples and 16 melanistic lesion samples to develop a partial transcriptome—the ribonucleic acid (RNA) instructions inside a cell. The abundance of 55 genes associated with contaminant exposure, melanogenesis, immune response, and a unique viral helicase-like gene were measured. Eleven of 55 genes analyzed were differentially expressed between melanistic and normal skin tissues. Three of those were unique gene sequences, two of which were unidentified and one was a viral gene. The viral gene was detected in 12 of the 16 melanistic areas and in no normal skin samples. The viral gene sequence indicated a similarity to a newly recognized viral family, Adomaviridae, that has been associated with disease in other fish species.
Further research is underway to fully characterize the virus and understand the mechanisms involved in the formation of melanistic lesions and to determine the role of environmental factors, such as temperature and chemical contaminants, in initiation and progression of the lesion.
This research was funded by the Pennsylvania Fish & Boat Commission, the Pennsylvania Sea Grant College Program, and the USGS Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) of the Ecosystems Mission Area, and the Environments and Fisheries Program.
- Science
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Fish mercury data from State monitoring programs and research studies within the Chesapeake Bay were compiled and summarized to provide a comprehensive overview of the variation in fish mercury concentrations among species and habitats within the watershed. These data are put into context with existing health benchmarks for humans, birds, and fish. Scientists also provide a roadmap for an...Prevalence of Malignant Melanoma in Brown Bullhead from Lake Memphremagog Greater than Expected—Linkages to Contaminant Exposure and Implications for Fish Population Health are Currently Unknown
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Mercury isotope analyses were used to distinguish different sources of mercury to fish in 23 streams along a forested-rural to urban-industrial land-use gradient in the Northeastern United States. The use of mercury isotope measurements in fish tissue allow for distinguishing different sources of mercury that are bioaccumulating into the food web. Mercury isotope signatures in fish in forested...Intersex in Male Smallmouth Bass in the Missisquoi River in Vermont: Understanding Factors that Can Lead to Endocrine Disruption in Field Settings
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... - Publications
Below are publications associated with this research.
Hyperpigmented melanistic skin lesions of smallmouth bass Micropterus dolomieu from the Chesapeake Bay watershed
Hyperpigmented melanistic skin lesions (HPMLs) of smallmouth bass Micropterus dolomieu are observed in the Potomac and Susquehanna rivers, Chesapeake Bay watershed, USA. Routine, nonlethal population surveys were conducted at 8 sites on the mainstem Susquehanna River and 9 on the Juniata River, a tributary of the Susquehanna River, between 2012 and 2018, and the prevalence of HPMLs was documented.AuthorsVicki S. Blazer, Kelsey T. Young, Geoffrey D. Smith, Adam Sperry, Luke R. Iwanowicz