Walleye dermal sarcoma (WDS) was first described as a multifocal cutaneous neoplasm of walleyes Stizostedion vitreurn in Oneida Lake, New York, USA. The neoplasm was subsequently shown to be caused by a type C retrovlrus. We have successfully transmitted the neoplasm in laboi-atory-maintained young-of-the-year (YOY) ~r a l l e~e s In a number of pathogenesis studies over the past 6 yr. Neoplasms in these laboratory trials were typical of those superficial neoplasms observed in adult feral walleyes. A transmission study was begun summer 1994 uslny 9 \vk old walleyes. S t a r t~n g at 56 d and continuing throughout the experiment, injected fish developed grossly visible, multiple small whlte skin masses that varled from 0.5 to 10 mni in diameter. These masses appeared on the skin of the head, back, flank, fins and lips. Histopathological examination revealed that some of these neoplasms, especially those collected at 84 d and beyond, did not remain cutaneous, but were locally invasive and replaced normal tlssue, primanly muscle. One neoplasm on the head of a young walleye had deformed the brain and had invaded the skull. Due to the unusual invasive nature of the microscopic lesions of the neoplasm, these findings are reported.
Nile tilapia Oreochromis niloticus, summer flounder Paralichthys dentatus, and walleyes Sander vitreus were treated with Romet-30 (PHARMAQ AS, Oslo, Norway) via a medicated ration at 50 mg Romet-30 kg fish body weight(- 1) d(-1) for 10 d to compare the elimination kinetics of the test substance. This study was part of a larger effort to develop a species grouping concept for the labeling of therapeutic compounds for cultured fishes. The fish tests were conducted at the ideal water temperature for each species and at 5 degrees C lower than the ideal temperature except for summer flounder, which would not feed at the lower temperature of 15 degrees C. Test temperatures were 30 degrees C and 25 degrees C for Nile tilapia, 20 degrees C and 17 degrees C for summer flounder, and 25 degrees C and 20 degrees C for walleyes. Neither component of Romet-30 (sulfadimethoxine and ormetoprim) could be detected in samples of the edible portion of walleyes (muscle plus skin) collected at day 10 posttreatment or thereafter. In studies with summer flounder, only one fish had a detectable concentration of either component on day 21 or thereafter. Elimination of Romet-30 by Nile tilapia was extremely rapid. The limited number of Nile tilapia with detectable sulfadimethoxine or ormetoprim during the posttreatment period prevented the determination of elimination half-life or elimination in this species.
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