Nematodes of the intestine and swim bladder of the European eel Anguilla anguilla [L.] ascending Pomeranian rivers

The study focused on the eel (length and weight averaging 23.1 cm and 13.7 g, respectively) ascending Pomeranian rivers in summers of 1999-2003. The swim bladder was examined in 322 individuals, the intestine being examined in 272 fish. Anguillicola crassus was present in the swim bladder of 184 fish. Infection prevalence varied between the rivers, the highest prevalence being recorded in the eel caught in the Radew (65.6%) and the lowest in the Wieprza (41.7%). The intensity of infection was generally low, the mean values varying from 2. l in the Rega to 1.3 in the Wieprza. The coefficient of infection was low (0,11 to 0,12). Spinitectus-inermis was present, with low intensity, in the intestine of 18 fish (6.6%). The nematode had not been recorded in the eel in Poland for 70 years. In addition, the intestine of the eel under study was found to house Raphidascaris acus and Paraquimperia tennerima, each present as a single larva. This is the first record of the latter in Poland. The infection of eel from the Radew river that stayed in the fresh water for a longer time was higher than that of the eel found in the Rega and Wieprza.