Abstract

In fall 1996 and spring 1997, watermen along the Pocomoke River, a tributary of the Chesapeake Bay on the lower Delmarva Peninsula, noted an increased frequency of lesions among the fish in their catch. Lesions appeared on numerous species of fish and varied considerably, ranging from small foci of petechial hemorrhage to extensive areas of ulceration extending through the integument to underlying tissues. Some watermen also reported overall decreased body condition among their catch. Subsequent scientific investigations undertaken to establish the cause(s) for these lesions also revealed that there was a paucity of any previously established “normal” baseline data concerning the health of fish within the Chesapeake Bay ecosystem.

In 1998, a cooperative 3-year research effort between scientists from the U.S. Geological Survey, the Maryland Department of Natural Resources, and North Carolina State University was initiated in order to establish baseline fish health data for white perch (Morone americana), a representative species of fish, among Chesapeake Bay tributaries, and to compare health related parameters among these fish from different tributaries. In 1998 and 1999, 24 white perch were collected from five Chesapeake Bay tributaries by net trawls at three different sampling periods (June, August and October) each year. Data were collected from the specimens via a necropsy-based fish health assessment protocol incorporating both gross and histologic observations and characterization of lesions. Blood was collected for hematologic analyses including hematocrit, plasma protein concentration, and total/differential leukocyte counts. Tissue was also collected from hematopoietic kidney and spleen for immunologic functional analyses including lymphocyte mitogenesis assays, macrophage bactericidal assays, and cytokine (transforming growth factor-β) expression analysis. Water quality data and watershed land use data were also collected for each sampling interval/site to further discern any spatial differences noted in the health-related parameters.

Sampling for the first 2 years of the study is completed and data analysis is currently underway. Preliminary findings have established that a variety of gross lesions were apparent on the white perch from the 1998 and 1999 collections, ranging from incidental, such as mildly frayed fins to severe, such as extensive multifocal hemorrhage. Leukocyte functional analyses indicate that significant temporal and spatial differences in immune cell function exist for white perch in the tributaries surveyed. Hematologic data also indicate a few potential differences between sites as well as over time.