Studies on the transmissibility and etiology of orocutaneous tumors of brown bullheads Ictaiurus nebulosus

Abstract

To determine the transmissibility of orocutaneous neoplasms of brown bullheads Ictalurus nebulosus under laboratory conditions, 120 test fish were inoculated with cell-free, filtered tumor homogenate or with live neoplastic cells prepared from pooled neoplasms collected from adult fish in the spring. Controls received vehicle alone or cells from a homologous cell line (BB). Inoculated fish were kept at 10. 15. and 20 "C. The disease was not transmitted in this 9 mo trial. Electron microscopic examination of the 2 inocula did not reveal viral particles. No cytopathic effects were observed in primary cultures of neoplastic cells or in BB monolayers inoculated with material derived from the neoplasms. Neither a mixed bovine papillomavirus and cottontail rabbit papillomavirus DNA probe (BPV-CRPV) nor a fish retrovirus probe (WDSV) recognized any homologous sequences on Southern blots of brown bullhead neoplasms. However, RNA-dependent DNA polymerase activity, presumably reverse transcriptase, absent from normal brown bullhead skin, was detected in neoplastic tissue and preferred Mn2+ as the divalent cation. Results suggest that the etiology of orocutaneous neoplasms of brown bullheads is probably multifactorial and integrated into the broad scheme of multistep carclnogenesis.