Gregory A. Wooster

SEASONAL PREVALENCE OF SKIN TUMORS FROM WALLEYE (STIZOSTEDION VITREUM) FROM ONEIDA LAKE, NEW YORK

A seasonal survey of skin tumor prevalence in walleyes (Stizostedion vitreum) was conducted during the ice-free period on Oneida Lake, New York in 1986. During the survey, 1,028 walleyes were collected and examined for the presence of lymphocystis disease, dermal sarcoma, discrete epidermal hyperplasia and diffuse epidermal hyperplasia. Skin growths were high in prevalence in early spring, low in prevalence during the summer, and again high in prevalence in the fall. Lymphocystis disease and dermal sarcoma were more frequently observed than either discrete or diffuse epidermal hyperplasia. Histologically, a moderate to severe inflammatory response was associated with dermal sarcoma in the early spring and late spring but not in the fall. Regardless of the time of year, varying degrees of inflammatory response were seen associated with lymphocystis disease. Samples were inadequate to assess seasonal trends in incidence of discrete and diffuse epidermal hyperplasia.

Blood chemistry of healthy, nephrocalcinosis-affected and ozone-treated tilapia in a recirculation system, with application of discriminant analysis

Blood chemistry parameters of Nile tilapia (pure strain Oreochromis niloticus) raised in a recirculation system were studied. Plasma samples were collected from 30 healthy tilapia every 3 months during a 1-year period. An additional 30 tilapia affected with nephrocalcinosis, and 30 fish from a system treated with ozone were also examined. Significant differences among healthy groups were observed in all parameters except for plasma magnesium, iron, albumin-to-globulin ratio, glucose, cholesterol, and alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphotase (AP) and creatine kinase (CK) activities. Nephrocalcinosis-affected tilapia differed significantly from healthy fish in most electrolyte and metabolite concentrations, as well as in ALT, AST and AP activities. Ozone-treated fish showed significant differences in electrolyte concentrations and ALT, AST and AP activities. Discriminant analysis revealed good separation of these groups. Evaluation of the data set indicated that the number of blood chemistry parameters could be reduced from 23 to 9 without losing the ability to separate the groups (90% and 92% correct, respectively). Most of the incorrect prediction came from less satisfactory separation of ozone-treated fish from healthy fish, due to the lack of apparent adverse impact on health of this treatment. Thirty tilapia from the same facility that were experiencing a low mortality rate were also used to test the model; individuals with abnormal blood chemistry profiles were identified.

Effects of Thiamine on Reproduction of Atlantic Salmon and a New Hypothesis for Their Extirpation in Lake Ontario

Abstract Previous researchers demonstrated that a mortality in fry (called Cayuga syndrome) of Atlantic salmon Salmo salar from Cayuga Lake (New York) was associated with low levels of thiamine. They reduced the mortality of fry by bathing or injecting fry with thiamine. We injected four to six gravid female Atlantic salmon with either physiological saline (PS) or PS plus thiamine (7 mg/kg weight) 14–23 d before eggs were stripped, fertilized, and incubated in individual lots. Chemical analyses showed that eggs from control and treated salmon contained 1.1 and 1.6 nmol thiamine/g, respectively. Thiamine injections had no significant effect on the percentage of eggs that hatched. Between 700 and 800 Celius degree-days postfertilization, control fry (saline) showed signs of Cayuga syndrome and a 45% incidence of mortality; in contrast, mortality was only 1.9% for fry that received thiamine. By 1,078 degree-days postfertilization, mean mortality of control fry was 98.6%, whereas that for thiamine-injected sa...

Experimental Transmission of a Dermal Sarcoma in Fingerling Walleyes (Stizostedion vitreum vitreum)

Dermal sarcoma is a benign skin tumor of adult walleyes (Stizostedion vitreum vitreum) with a suspected viral etiology. A laboratory study was initiated to determine if the tumor could be experimentally transmitted by inoculating young walleyes with materials prepared from tumors from adult fish. Eighty walleye fingerlings were divided into four groups of 20 fish each. Two groups were inoculated intramuscularly at 4 months of age either with live tumor cells or with cell-free filtrates of sonicated tumor cells. The two other groups were used as controls and were inoculated either with cultured cells from normal walleye fry or with tissue culture media. Neoplasms, similar to the dermal sarcoma affecting adult walleyes, were observed after 4 months only in fingerlings inoculated with cell-free filtrates of sonicated tumor cells. Like the tumor affecting wild adult walleyes, the transmitted tumors were restricted to the dermis and originated from the superficial surface of scales. They never invaded locally and never metastasized. The transmitted tumors differed from tumors of adult walleyes in their severity and the absence of osteoid. The multicentric origin of transmitted walleye dermal sarcoma suggests that the virus spreads systemically and that tumor cells are polyclonal. This successful transmission of the lesion, along with the presence of C-type virus particles budding from tumor cells in two of seven tumor-bearing fingerlings, supports a retroviral etiology.

Histologic and Ultrastructural Studies of Dermal Sarcoma of Walleye (Pisces: Stizostedion vitreum)

Sixty-seven adult walleye fish were examined by light and transmission electron microscopy. The fish were affected by a mesenchymal tumor previously termed Walleye Dermal Sarcoma that commonly affects up to 27% of the population seasonally. Biopsies from 24 fish were collected, and complete postmortem examinations were performed on 43 fish. Grossly, the tumors had the appearance of randomly distributed, often clustered, spherical nodules, 2-5 mm in diameter with a smooth and often ulcerated surface. The tumors arose from the superficial surface of scales and consisted of fibroblast-like cells separated by a moderate amount of collagen (43/67) or osteoid material (24/67). Lymphocytic infiltration (28/67) associated with vacuolar degeneration of tumor cells (28/67) and centrally located coagulation necrosis (30/67) were observed. Although tumor cells were often highly anaplastic, no local invasions or metastases were present. In contrast with previous descriptions of this tumor, no viral particles could be observed electron microscopically. The variably anaplastic appearance of the tumor, its biological behavior, and its restriction to dermis are features in common with canine cutaneous histiocytoma and equine sarcoid. The multicentric origin, the restriction to the dermis, and the absence of invasion or metastases of Walleye Dermal Sarcoma differ from retrovirus-induced avian and murine sarcomas that arise locally, that invade, and that often metastasize.

Immunohistochemistry and pathology of multiple Great Lakes fish from mortality events associated with viral hemorrhagic septicemia virus type IVb

A novel viral hemorrhagic septicemia virus (VHSV) (genotype IVb) has been isolated from mortality events in a range of wild freshwater fish from the Great Lakes since 2005. In 2005 and 2006, numerous new freshwater host species (approximately 90 fish from 12 different species) were confirmed to have VHSV by cell culture and reverse transcriptase polymerase chain reaction. A prominent feature observed in infected fish were the petechial and ecchymotic haemorrhages on the body surface and in visceral organs, as well as serosanguinous ascites; however, many fish had few and subtle, gross lesions. Histologically, virtually all fish had a vasculitis and multifocal necrosis of numerous tissues. Excellent correlation was found between the presence of VHSV IVb antigen detected by immunohistochemistry and the pathological changes noted by light microscopy. Intact and degenerate leukocytes, including cells resembling lymphocytes and macrophages, also had cytoplasmic viral antigen. By contrast, renal tubules and gonadal tissues (ovary and testis), were strongly immunopositive for VHSV IVb, but no lesions were noted.

Communications: Comparison of Fall and Spring Tumors as Inocula for Experimental Transmission of Walleye Dermal Sarcoma

Abstract To determine if the walleye dermal sarcoma virus (WDSV) was present in both spring regressing tumors and fall developing tumors, an experimental transmission trial was conducted with cell-free tumor filtrates. A relatively high portion (82%) of young-of-the-year (age-0) walleyes Stizostedion vitreum inoculated with filtrates of spring-collected tumors developed dermal sarcomas. Conversely, no dermal sarcomas were observed on age-0 walleyes inoculated with filtrates of a tumor collected in the fall. Northern blot analysis demonstrated high levels of WDSV RNA in spring tumors and in inoculum derived from spring tumors, but very little viral RNA was detectable from fall tumors or inoculum derived from fall tumors.

Oxytetracycline Residues in Four Species of Fish after 10-Day Oral Dosing in Feed

Abstract Residues of oxytetracycline (OTC) in serum, liver, and muscle–skin were measured in sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis), Nile tilapia Oreochromis niloticus, summer flounder Paralichthys dentatus, and walleyes Sander vitreus (formerly Stizostedion vitreum). These studies were conducted to compare the time for OTC concentrations to fall below 2.0 μg/g (the current tolerance set by the U.S. Food and Drug Administration (USFDA)) among fish species representing various culture conditions of freshwater and salt water as well as different temperature niches. The sum of mean tissue OTC concentration plus two standard deviations in the edible portion (muscle plus skin) of all fish was below 2.0 μg/g at 11 d postdosing. When possible, depletion data were fitted to a one-compartment pharmacokinetic model. Although temperature niche did not appear to consistently affect residue depletion within species, the warmwater species (sunshine bass and Nile tilapia) ofte...

Effects of Fish Age and Challenge Route in Experimental Transmission of Walleye Dermal Sarcoma in Walleyes by Cell-Free Tumor Filtrates

Abstract To determine the effects of fish age at challenge and of challenge route on transmission of walleye dermal sarcoma, 25-week experimental transmission trials were conducted with cell-free tumor filtrates. Invasive dermal sarcomas developed in walleyes Stizostedion vitreum receiving intramuscular injections of tumor filtrate at 6 or 8 weeks posthatch. Invasive tumors were observed in few (5%) 12-week-old fish and in no 1-year-old fish injected with the tumor filtrates. Fish challenged at 12 weeks after hatching via topical application of inoculum or via oral gavage also developed walleye dermal sarcoma. Fish challenged via gavage developed tumors at a variety of locations on the body and fins. Again. invasive tumors were seen in few of the 12-week-old fish challenged by topical application (3%) or gavage (10%). However, several fish challenged via gavage developed severe tumors in the oral cavity and on the head near the oral cavity. Fish challenged via topical application of the inoculum developed...

Regression of Dermal Sarcoma in Adult Walleyes

Abstract Dermal sarcoma is a benign skin tumor of walleyes Stizostedion vitreum, and a seasonal prevalence for this condition has been observed in feral fish. This study was conducted to determine if dermal sarcomas regress. Evidence of dermal sarcoma regression was documented on individually identified adult walleyes. Degree of regression was variable, ranging from none to complete. This report provides the first definitive evidence that dermal sarcoma does regress seasonally from spring to summer.