Taxonomic Identification of Rhabdochona Species Found in Oncorhynchus Clarki Using Scanning Electron Microscopy

Extract

Adult Rhabdochona nematodes, commonly parasitizing fish, were present in the digestive tracts of cutthroat trout in Little Cottonwood Creek, Utah. Cutthroat trout, Oncorhyncus clarki, are known to serve as both intermediate and definitive hosts for parasitic nematodes. The larval stage parasitizes almost any tissue of its host, but the adult is always found in the digestive tract. Due to the lack of key morphological features, scanning electron microscopy (SEM) was used to identify specific structures leading to the nematode's taxonomic identification.

Cutthroat trout were obtained using a rod and reel and were dissected the same day. Nematodes were present in all 12 cutthroat trout residing in all parts of the digestive tract. The nematodes, Rhabdochona sp., were prepared for SEM using the following procedures. First, the parasites were fixed in 2% buffered glutaraldehyde, washed in sodium cacodylate buffer, and post fixed in a 1% solution of osmium tetroxide. The samples were then washed in the same buffer system and dehydrated through a graded alcohol series. Critical-point-drying removed the remaining fluids. Finally, the nematodes were placed on specimen stubs, sputter coated with gold, and each specimen examined with a JOEL-840 high resolution scanning electron microscope with micrographs taken at varying magnifications.