Rates of swim bladder parasite infection and PIT tag retention in upstream migrant American eels of the upper Potomac River drainage

Abstract

Rates of Swim bladder Parasite Infection and PIT Tag Retention in Upstream Migrant American Eels of the Upper Potomac River Drainage Jennifer L. Zimmerman This thesis involved two components: identification of the parasite Anguillicola crassus in American eels, Anguilla rostrata and PIT tag retention in eels in a laboratory setting. The recent spread of the swim bladder nematode parasite, Anguillicola crassus, in American eels has caused concern among biologists and fishery managers. A total of 244 yellow-phase American eels were collected at the Millville Dam eel ladder on the Shenandoah River, WV. Swim bladders were removed and examined for the presence of the nematode parasite. The number of parasites in each eel was recorded, and prevalence, intensity, and mean intensity were calculated. A swim bladder degenerative index (SDI) was also used on a subsample of 50 eels to document previous infections and the health state of the swim bladder. Prevalence of the parasite was 2%, and both intensity and mean intensity were 1. Based on the SDI, 38% of the eels showed signs of a previous infection of A. crassus. None of the eels from the Shenandoah River had severely degraded swim bladders, 38% had moderately damaged swim bladders, and 62% had healthy swim bladders. This is the first study that confirms the presence of A. crassus in the Potomac River watershed and the first to document the parasite in West Virginia. For the second part of the thesis, retention rates of passive integrated transponders (PIT tags) were compared among three tagging locations of small (205-370 mm) American eels: the dorsal musculature behind the head, the dorsal musculature near the dorsal fin origin, and the abdominal cavity. Eighteen American eels from the Shenandoah River, WV were PIT tagged in the three locations and tag retention was measured for a total of 9 weeks. Tag retention was highest in the dorsal musculature (100%) and in the abdominal cavity (100%), and lowest behind the head (88%). These results are consistent with previous literature. This research was a pilot study to determine PIT tag placement for a study of upstream migration in American eels.