Demographics and Parasites of Spotted Bass in the Wabash River

Spotted Bass Micropterus punctulatus Rafinesque are a popular sport fish primarily found in the streams and reservoirs of the south. The Wabash River, a large tributary of the Ohio River, contains a naturally reproducing population on the northern boundary of their range. Currently, the lower Wabash River is monitored using two different sampling designs, the Long Term Electrofishing Program monitors community assemblages using stratified random sampling whereas the Illinois Department of Natural Resources uses a fixed sampling design. Due to the wide distribution but low abundance of Spotted Bass throughout this drainage, captures from each design were compared to assess differences in abundance and size structure. Demographic data collected from each sampling design suggests that this population is of low density primarily composed of small individuals specific to particular habitats. The findings of this study suggest random sampling designs should be used when monitoring low density populations of fishes in a large riverine systems because this method provides the greatest spatial coverage of habitats, evaluates heterogeneity in distribution, and provides a representative measure of abundance throughout an entire aquatic system. Black bass, including Spotted Bass, are the top predatory species in most Midwestern rivers and reservoirs. Like many fishes, they exhibit ontogenetic shifts in habitat use and diet, resulting in selection of different prey items and the use of specific habitats throughout their life history. These shifts could lead to different parasite assembladges within different size classes of Spotted Bass. In 2014 and 2015, a subsample of 126 Spotted Bass ranging in size from 34 - 399 mm were necropsied and examined for helminths. Eleven parasites taxa (1 Acanthocephala, 4 Trematoda, 1 Cestoda, 1 Crustacea, 4 Nematoda) were recovered. All parasites recovered from Spotted Bass have been previously reported and are common within many other fish species. With the exception of Posthdiplostomum minimum centrarchi, prevalence of all other parasites was relatively low. Total length of the host was positively associated with total parasite abundance, parasite richness, and prevalence of individual helminth taxa, all of which are likely due to differences in exposure and changes in diet. Overall, the parasite community in Spotted Bass from the Wabash River exhibited low prevalence, abundance, and diversity resembling the characteristics of an isolationist community