Morphological Variation of Allocreadium Lobatum (digenea: Allocreadiidae) in the Creek Chub, Semotilus Atromaculatus (osteichthyes: Cyprinidae), in Nebraska, Usa

Allocreadium lobatum Wallin 1909, a parasite of freshwater fish, was originally described as having distinct lobate testes, and subsequent descriptions have left this original description unchanged. The present study quantifies the observation of distinctly non-lobate testes that could be categorized as round or asymmetrical in addition to the previously described lobate testes. Six hundred thirty sixA. lobatum were collected from 228 Semotilus atromaculatus over a 9 month period. Overall, 21.3%, 61.6%, and 16% were found to be round, asymmetrical, and lobate testes respectively (N = 1071). Analysis of testis morphology found the increasing presence of lobate testis as the length of A. lobatum increased, being the prominent morph in parasites > 40 mm. Analysis of previous studies in Nebraska and Idaho, USA, confirm the presence of all three testicular categories, with a predominance of lobate testes in 9 of the 12 studies. Complete morphological analyses of A. lobatum over this study period are reported and demonstrate greater variation than did previous studies.