Pigmented subcutaneous spindle cell tumors in native gizzard shad (Dorosoma cepedianum)

Abstract

An epizootic of pigmented subcutaneous spindle cell tumors affected nearly 25% of the adult gizzard shad (Dorosoma cepedianum) sampled from Lake of the Arbuckles in central Oklahoma over a 2 year period. Grossly, the tumors were primarily distributed over the head, trunk and fins as superficial raised masses that were almost always darkly pigmented. Histologically, they were located in the dermis, had a variable amount of connective tissue, and consisted of cells in a variety of forms and arrangements. Most tumors were composed of fusiform or spindle cells arranged in wavy bundles, whirling patterns or interwoven fascicles. Pigmentation was attributed to large dense deposits of melanin or to scattered individual melanin-containing cells. Immunohistochemical detection of proliferating cell nuclear antigen revealed a high proliferative activity in the spindle cells. Electron microscopy showed that the tumors were composed of several cell types, including host reactive cells, melanocytes in stages of maturity, and fibroblast-like cells. Tumor cells had neither cell-to-cell junctions nor an external lamina. Although the cell of origin of the tumors was not identified, evidence points toward melanocytes or, possibly, nerve sheath cells. However, an origin from fibroblasts or some other poorly differentiated cell cannot be ruled out. The etiology of the tumors was not determined. Fractionation of lake water and sediment samples followed by GC-MS analysis revealed no carcinogenic compounds. A retroviral etiology is unlikely because assays for reverse transcriptase in tumor homogenates were negative, and no evidence of viral particles was found in specimens examined by electron microscopy.

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 ϭ 0.469).…”

“…Fisher's exact test was used to determine differences in neoplasm occurrence in the gizzard shad populations between a Fish sampled before 1995 were previously reported [16,17]. Lake Texoma and Lake of the Arbuckles.…”

“…Fractionation of lake water and sediment samples followed by gas chromatography–mass spectrometry analysis revealed no carcinogenic compounds when compared to the spectra in the National Institute of Standards and Technology (NIST) database [18], in which more than 42,000 compounds are archived. Results of assays for reverse transcriptase indicating the presence of retrovirus in tumor homogenates were negative, and no evidence of viral particles were found in specimens examined by transmission electron microscopy [16]. Since those studies were published, additional cases of poorly differentiated dermal neoplasms have been found in other fish species from Lake of the Arbuckles, including a hemangiopericytoma from a white bass ( Morone chrysops ) [19], and poorly differentiated spindle‐cell neoplasms from two threadfin shad ( D. petenense ) (D.R.…”

“…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. Grossly, the tumors were primarily distributed over the head, trunk, and fins as superficial raised masses that were usually darkly pigmented but sometimes unpigmented.…”

“…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.…”