FISHERY BULLETIN: VOL. 76, NO. 4 



Figure 7. — Wartlike fibrous tumors in Mugil cephalus from Biscayne Bay, Fla. 



ing prevalences of similar epidermal papillomas 

 in flatfish from relatively unpolluted waters of 

 northern Japan felt that a possible association 

 existed between high tumor occurrence ( up to 20% 

 in certain samples) and parasitization of the flesh 

 by a nematode, Philometra marine, but then they 

 suggested that the involvement of naturally oc- 

 curring chemical contaminants as well as man- 

 made pollutants must be considered in the etiol- 

 ogy of flatfish neoplasms. 



Wellings et al. (1977) found 1.0% of rock sole, 

 Lepidopsetta bilineata, sampled in the still- 

 unpolluted Bering Sea, with epidermal papil- 

 lomas. Infections were widely distributed geo- 

 graphically, mostly in older individuals. The age 

 distribution of infection was quite different from 

 that in Puget Sound flatfishes, where predomi- 

 nantly younger fish are involved. 



The etiology of skin tumors in English sole from 

 the Pacific coast of North America was reviewed in 

 a recent paper by Angel et al. (1975), with the 

 conclusion that the cause is unknown, and may be 

 multifactorial. Three stages of tumorigenesis 

 were described in young-of-the-year English sole, 

 beginning with angioepithelial nodules and pro- 



gressing to epidermal papillomas and an- 

 gioepithelial polyps. No conclusive role of an en- 

 vironmental carcinogen has been demonstrated; 

 there seem to be subpopulation differences in dis- 

 ease prevalences; and electron microscopy has dis- 

 closed the presence of viruslike particles in cells of 

 papillomatous fish (Wellings and Chuinard 1964), 

 but attempts to isolate a viral agent have been 

 unsuccessful. 



To further complicate the story, an unknown 

 cell type, called an "X cell," has been found in all 

 three tumor stages in English sole. The cells may 

 be parasitic, as was suggested by Brooks et al. 

 (1969), and Alpers et al. (1977b), or they may be 

 transformed host cells, analogous to lymphocystis 

 cells, as was suggested by Angell et al. (1975). 

 Angell et al. concluded by stating that "given the 

 pervasiveness of certain pollutants, experimental 

 evidence and further field studies will be neces- 

 sary to clarify the relationship between tumorous 

 flatfishes and pollution." 



Another observation on the possible relation- 

 ship of flatfish tumors and pollutants has been 

 supplied by Mearns and Sherwood (1974). The dis- 

 tribution and abundance of skin tumors and fin 



730 



