Further investigations of the etiology of subcutaneous neoplasms in native gizzard shad (Dorosoma cepedianum)

Abstract

Aspects of the etiology of subcutaneous spindle‐cell neoplasms in feral gizzard shad (Dorosoma cepedianum) collected from Lake of the Arbuckles, Oklahoma, were investigated. Field collections of adult and juvenile gizzard shad were conducted to determine the prevalence and seasonality of neoplasms and site specificity of neoplasm‐bearing fish. Overall neoplasm prevalence for adult gizzard shad was 22.1%; no juveniles exhibited neoplasms. Neoplasm occurrence did not appear seasonal. Neoplasm‐bearing gizzard shad were found at all three sampling sites within Lake of the Arbuckles with similar neoplasm prevalence rates (Guy Sandy Creek 22.1%, Rock Creek, 17.9%, and Buckhorn Creek 22.4%). No gizzard shad (juvenile or adult) collected from Lake Carl Blackwell, Oklahoma, the reference site, exhibited neoplasms. Water, sediment, and shad liver tissue from Lake of the Arbuckles and the reference site were analyzed for total recoverable metals (cadmium, chromium, copper, nickel, and lead, by graphite furnace atomic absorption). Chromium, copper, and nickel were found in the water samples at concentrations of >1 to 8.6 μg/L. Low concentrations (>1 to 13.6 μg/g wet weight) of all the metals were found in the sediment and liver tissue from both sites. Heavy metal contamination does not appear linked to neoplasm occurrence. To determine if a nonbacterial infectious agent was responsible for tumor formation, cell‐free neoplasm homogenates were injected into healthy rainbow trout. Neoplasms were not transmitted into rainbow trout. The etiology of these neoplasms remains unknown.

Pigmented skin tumors in gizzard shad (Dorosoma cepedianum) from the south‐central United States: Range extension and further etiological studies

“…Gizzard shad collected from the Lake of the Arbuckles had a total neoplasm prevalence of 15.4% (73/474), which was lower than that reported in previous studies (21.01%, 208/990) [16,17] (Table 1). However, statistical testing for differences between results from previous studies and those from the current study failed to reveal a difference in neoplasm prevalence ( p = 0.469).…”

“…The cell of origin in the gizzard shad neoplasm has not been definitively determined [16,17]. Two major possibilities are pigment cells and peripheral nerve sheath cells.…”

“…The present study involved an epizootic of pigmented subcutaneous spindle‐cell neoplasms previously reported in gizzard shad ( Dorosoma cepedianum ) from Lake of the Arbuckles, a manmade lake in central Oklahoma, USA [16,17]. In those studies, lesions were found in about 22% of adult gizzard shad and in 0% of nearly 2,000 juvenile shad examined.…”

“…Likewise, there were no differences in tumor incidence between adult males and females. Results of transmissibility studies conducted with rainbow trout injected with cell‐free extracts of gizzard shad neoplasm were negative [17]. Ostrander et al [16] described the appearance, distribution, and histological characteristics of the shad tumors.…”