Non-Invasive Technique for Assessing the Population Parameters of Metacercariae of Clinostomum marginatum in Smallmouth Bass (Micropterus dolomieu)

Clinostomllm marginatum is a trematode that uses a fish as its final intennediate host. The wonns in the fish are in metacercarial cysts and are known as yellow grub. Yellow grubs give the fish's flesh a wonny, unappetizing appearance and are a problem for commercial fish fanners in that heavily infected fish are not suitable for marketing. The parasite is common in smallmouth bass (Micropterus dolomieu) living in upland streams of Arkansas where the bass may serve as a wild reservoir for contamination of commercial fish ponds. Because smallmouth bass are a prized game fish, it would be desirable to be able to assess the extent of yellow grub infections by a non-invasive method whereby the fish could be examined and returned to its habitat without destructive necropsy. In this study strong correlations were found between the parasites seen in the orobranchial region and the rest of the host body. These correlations were found for all of the population parameters usually reported. The significance of these findings are mainly three fold: (I) The correlations allowed a reasonable estimate of yellow grub loads in populations of smallmouth bass using only orobranchial counts, (2) in situ examination of the mouth and gills alone allows the fish to be returned unharmed to the stream and (3) similar anatomical-site density correlations applied to other parasitic infections might dramatically reduce the amount of necropsy time needed for estimating total parasite numbers. Examples for the latter are given from other studies with Clinostomum complanatum and Proteocephalus ambloplitis species that show similar anatomical site density relationships in their respective hosts.