White Grub Posthodiplostomum minimum centrarchi Metacercariae in the Liver of Largemouth Bass: Quantification and Effects on Health

White grub Posthodiplostomum minimum centrarchi is a digenetic trematode that parasitizes centrarchid fishes. The prevalence and density of white grub metacercariae in livers of largemouth bass Micropterus salmoides from Lake Holly and Lake Weir, Florida, were determined by two methods suitable for use with fixed tissue. Digestion of formalin‐fixed tissue was used to determine the number of metacercariae per gram of liver, and stereologic examination of histologic sections was used to determine the percentage of liver volume occupied by white grub cysts (volume percent). The results of these two methods were significantly related. The prevalence of white grub infection in largemouth bass was similar in these lakes; 94.1% for Lake Weir and 93.3% for Lake Holly. However, fish in Lake Weir had 119 metacercariae/g of liver and 4.6% of the liver volume was occupied by white grub cysts compared to only 20 metacercariae/g and 0.83% for fish from Lake Holly. There was no significant relation between the severity of white grub infection and hematocrit, relative weight, or growth of the fish. White grub densities were also unrelated to age, gender, total length, or weight of the fish.