Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

Spring 2019

Thesis Director

Jeffrey R. Laursen

Thesis Committee Member

Robert E. Colombo

Thesis Committee Member

Charles L. Pederson


White grub (Posthodiplostomum minimum) is a digenetic trematode that uses a piscivorous bird, a pulmonate snail, and a centrarchid fish to complete its life cycle. To assess the impact of impoundment and sewage effluent on white grub infection parameters, infections in bluegill (Lepomis macrochirus) were monitored in 3 reaches of the Sangamon River near Decatur, Illinois: Reach 1- free-flowing river upstream of Lake Decatur Dam, unimpacted by sewage effluent, Reach 2- impounded flow below Lake Decatur Dam, unimpacted by sewage effluent, and Reach 3- free-flowing river downstream of Sanitary District of Decatur, impacted by sewage effluent. Liver and kidney abundances of white grub were compared to bluegill condition indices to assess effects of parasite burdens on the intermediate fish host. Prevalence of white grub in the Sangamon River was 96.4%, with a mean abundance of 153.7 metacercaria per individual. White grub abundance was highest in Reach 2, followed by Reach 1, and lowest in Reach 3. In low level infections (<50 metacercariae), white grub had a significantly higher ratio of liver to kidney abundance, whereas bluegill with medium/high (>50 metacercariae) levels of infection, liver and kidney abundances were almost equal. Most condition indices (Relative weight, gonadosomatic index, and cortisol baseline levels) did not correlate with parasite burden. However, Fulton's condition score in small bluegill, typically with low level infections, was positively correlated with parasite burden.