American eels Anguilla rostrata are infected by an introduced parasitic nematode Anguillicoloides crassus, which can cause extreme necrosis of their swimbladders, yet effects on the eel population are currently unknown. We collected 3 eel life stages (glass, elver, and yellow) and the presence of A. crassus and swimbladder damage in each eel was quantified. The preliminary data show over 60% prevalence and an even higher prevalence of damaged swimbladders.