Temporal Trends in Macroscopic Indicators of Fish Health in the South Branch Potomac River

Over recent decades, the South Branch Potomac River, West Virginia, has experienced fish kills and episodes of suppressed health in adult fish that have spanned small stretches to nearly 120 km of contiguous habitat. Although factors such as endocrine disruption, chemical contaminants, and infectious agents have been detected, no single causal mechanism has been identified. To gain information about the temporal nature of abnormalities, differences in life stage impacts, and potential risk factors, investigations of rank scores of macroscopic fish health indicators were conducted utilizing seasonal and annual boat electrofishing surveys for Smallmouth Bass Micropterus dolomieu (SMB) and Golden Redhorse Moxostoma erythrurum (GDR). Gill and body abnormalities were assigned rank scores for each fish based on visual severity and were tested for correlation with seasonal climatic (flow and stream temperature) and environmental (stream pH, dissolved oxygen, and turbidity) factors. Comparisons between juveniles and adults for these species indicated that body lesions were more common for adult GDR and gill lesions were more common for adult SMB. Significantly higher rank sums of adult gill abnormalities corresponded with heavy annual mortality of SMB between ages 2 and 3 (86%), the period during which this species transitions from juvenile to adult length. Higher ranks were frequently assigned to fish of both species for gill and body/fin lesions in summer and fall samples. Low stream discharge and lower pH correlated with elevations of body raised lesions (GDR) and body erosions (GDR and SMB) as well as erosions of the gill lamellae (SMB). This study connects the disciplines of fisheries management, fish health, and environmental monitoring, providing information gained through tracking the macroscopic conditions of these two indicator species to focus future studies and better understand risks to fish health.