Adult and young of the year smallmouth bass from the Chesapeake Bay watershed have faced health issues (mortality events, disease by a variety of pathogens, endocrine disruption in male fish, evidence of oxidative damage to tissues, and signs of exposure to chemical contaminants) at multiple sites within the Susquehanna and Potomac River basins. Functional immune assays were added to long-term comprehensive monitoring assessments to determine if immunosuppression was playing a role in observed disease and mortalities because no one single or consistent cause could be identified. The functional immune assays measured bactericidal activity, respiratory burst activity, and lymphocyte mitogenesis using leukocytes isolated from anterior kidney tissue. From 2016-2021, a total of 740 smallmouth bass were sampled among eight (8) sites. Twenty adults were sampled from each site in spring (pre-spawn; April – May) and fall (recrudescence; October – November) at different points in the study. Ancillary data, including biometrics of the fish and parasite/macrophage aggregate counts in multiple tissue types, were collected in conjunction with the immune data. The functional immune assays serve as part of an integrated assessment to determine environmental stressors and infectious agents that may modulate the immune response in wild smallmouth bass, ultimately making them more susceptible to disease and death. Therefore, it is important to consider the functional immune data alongside other aspects of host and environmental health.

Biological indicators including morphometric (length, weight), age, sex and health indicators including organismal (health assessment index, condition factor), organ (hepatosomatic index, gonadosomatic index), cellular (intersex, parasite density, macrophage aggregate density), subcellular (plasma vitellogenin, estradiol, testosterone, 11-keto testosterone) and molecular (hepatic transcript abundance) were measured in smallmouth bass from tributaries in the Chesapeake Bay watershed. Total mercury was measured in these fish and correlations between mercury and biological indicators were assessed.

Biological indicators including morphometric (length, weight), age, sex and health indicators including organismal (health assessment index, condition factor), organ (hepatosomatic index, gonadosomatic index), cellular (intersex, parasite density, macrophage aggregate density), subcellular (plasma vitellogenin, estradiol, testosterone, 11-keto testosterone) and molecular (hepatic transcript abundance) were measured in smallmouth bass from tributaries in the Chesapeake Bay watershed. Total mercury was measured in these fish and correlations between mercury and biological indicators were assessed.

In 2016, smallmouth bass were collected from three sites in the Lake Erie drainage in Erie County, Pennsylvania and an out-of-basin site in the Allegheny River drainage in order to assess reproductive health and identify endocrine disruption responses. Pieces of liver and gonad were taken in Z-Fix and RNALater for histology and transcript abundance analysis. A landscape analysis was conducted for the immediate and upstream catchments with 2016 land cover data. Correlations between biological variables and transcripts were made in addition to differences between sites. The results showed that males had biological variables that correlated with transcripts associated with endocrine disruption and a high rate of testicular oocytes and plasma vitellogenin (biomarkers of estrogenic contaminant exposure).

In 2016, smallmouth bass were collected from three sites in the Lake Erie drainage in Erie County, Pennsylvania and an out-of-basin site in the Allegheny River drainage in order to assess reproductive health and identify endocrine disruption responses. Pieces of liver and gonad were taken in Z-Fix and RNALater for histology and transcript abundance analysis. A landscape analysis was conducted for the immediate and upstream catchments with 2016 land cover data. Correlations between biological variables and transcripts were made in addition to differences between sites. The results showed that males had biological variables that correlated with transcripts associated with endocrine disruption and a high rate of testicular oocytes and plasma vitellogenin (biomarkers of estrogenic contaminant exposure).

Monitoring wild fish health and associated exposure effects in regions where agriculture and development have impacted rivers and streams has become a valuable research tool. Smallmouth bass (Micropterus dolomieu) are a sensitive, indicator species that exhibit symptoms of immunosupression and endocrine disruption in response to water quality changes and contaminant exposure. In the Susquehanna River drainage, smallmouth bass have been used in biomonitoring assessments to help understand changes in the population due to poor young-of-the-year recruitment and health effects. To help determine effects of agriculture and development on smallmouth bass health, two sites (a developed/agriculture site and a forested site) were selected where bass and water chemistry were sampled from 2015-2019. Bass were sampled for histopathology to assess parasite and macrophage aggregate density in the liver and spleen, condition factor (Ktl), hepatic gene transcripts (immune function, oxidative stress, cell proliferation, stress, and contaminant, thyroid, and insulin/pancreas metabolism), hepatosomatic index (HSI), and a health assessment index (HAI). Land use at the developed/agricultural site included greater pesticide application rates and % high phytoestrogen crop cover and there were more detections and higher concentrations of pesticides, wastewater-associated contaminants, hormones, phytoestrogens, and mycotoxins than at the forested site. Additionally at this site, oxidative stress, lipid metabolism, and thyroid-related hepatic gene transcripts were associated with contaminants/land use applications; whereas at the forested site there were far fewer associations. At both sites, there were multiple associations of contaminants/land use applications with biological variables (HSI, Ktl, and liver and spleen macrophage aggregate density), which may indicate that changes at the molecular level may be a better indicator of exposure effects unique to each site. This work will help to understand the importance of timing for land management practices, how contaminants change temporally, and that agricultural practices affect hepatic gene transcripts associated with immune function and disease resistance and may negatively affect the health of smallmouth bass.

Monitoring wild fish health and associated exposure effects in regions where agriculture and development have impacted rivers and streams has become a valuable research tool. Smallmouth bass (Micropterus dolomieu) are a sensitive, indicator species that exhibit symptoms of immunosupression and endocrine disruption in response to water quality changes and contaminant exposure. In the Susquehanna River drainage, smallmouth bass have been used in biomonitoring assessments to help understand changes in the population due to poor young-of-the-year recruitment and health effects. To help determine effects of agriculture and development on smallmouth bass health, two sites (a developed/agriculture site and a forested site) were selected where bass and water chemistry were sampled from 2015-2019. Bass were sampled for histopathology to assess parasite and macrophage aggregate density in the liver and spleen, condition factor (Ktl), hepatic gene transcripts (immune function, oxidative stress, cell proliferation, stress, and contaminant, thyroid, and insulin/pancreas metabolism), hepatosomatic index (HSI), and a health assessment index (HAI). Land use at the developed/agricultural site included greater pesticide application rates and % high phytoestrogen crop cover and there were more detections and higher concentrations of pesticides, wastewater-associated contaminants, hormones, phytoestrogens, and mycotoxins than at the forested site. Additionally at this site, oxidative stress, lipid metabolism, and thyroid-related hepatic gene transcripts were associated with contaminants/land use applications; whereas at the forested site there were far fewer associations. At both sites, there were multiple associations of contaminants/land use applications with biological variables (HSI, Ktl, and liver and spleen macrophage aggregate density), which may indicate that changes at the molecular level may be a better indicator of exposure effects unique to each site. This work will help to understand the importance of timing for land management practices, how contaminants change temporally, and that agricultural practices affect hepatic gene transcripts associated with immune function and disease resistance and may negatively affect the health of smallmouth bass.

Environmental DNA results for March 2022 smallmouth bass surveillance in the Gardner River, Montana

Environmental DNA results for March 2022 smallmouth bass surveillance in the Gardner River, Montana

Disease outbreaks, skin lesions, fish kill events, and reproductive abnormalities have been observed in wild populations of bass in the Chesapeake Bay watershed. Occurrence of synthetic and natural hormones from wastewater treatment plants and livestock operations, pesticides from agricultural lands, and phytoestrogens from cover crops have been implicated as potential causes of these adverse effects. Late summer to fall is the period of early gonad recrudescence in adult bass when spermatogenesis and oogenesis begin for the upcoming spawning event in spring. Our objective was to assess whether early gonad recrudescence was a period of sensitivity for inducing immunomodulation. Adult largemouth bass (LMB; Micropterus salmoides) were exposed in outdoor pond mesocosms from post-spawning (July) through early gonad recrudescence (November) to either a model estrogen, 17alpha-ethinylestradiol (EE2; 2.4 ng/L), a mixture of endocrine-active substances commonly detected in the Chesapeake Bay watershed (MIX; 5.4 µg atrazine/L and 47.9 ng estrone/L), or a solvent control. Immune endpoints including mitogenesis and respiratory burst were assessed in fish sampled during December and April.