4r 



E 

 E 



c 



a> 



11 



14 



Days 



Figure 2. — Regenerative growth of tail fin of Fundulus heter- 

 oclitus exposed to methylmercury and zinc in seawater, Exper- 

 iment I. 



Key: A 10.0 ppm Zn (n = 15), V 3.0 ppm Zn(n = 15), D 1.0 ppm 

 Zn (« = 15), C Control in = 14), A 0.05 ppm meHg + 10.0 ppm 

 Zn {n = 11), ▼ 0.05 ppm meHg + 3.0 ppm Zn {n = 12),  0.05 

 ppm meHg + 1.0 ppm Zn in = 9), • 0.05 ppm meHg (n = 12). 



Table 3. — Average mercury uptake (ppm Hg/wet weight ± SE) 

 by Fundulus heteroclitus. 



'n.d. = not detectable, <0.03ppm. 



into the brain or the rest of the body. Accumula- 

 tion of zinc was not altered by methylmercury. 

 Animals in 10 ppm Zn accumulated 246±1.41 

 ppm; those in 10 ppm Zn + 0.05 ppm meHg ac- 

 cumulated 250±3.54 ppm. Those in 1 and 3 ppm 

 Zn accumulated 221±25.2 and 250±4.95 ppm, 

 showing no clear dose-dependent relationship. 



Discussion 



The data indicate that in F. heteroclitus, zinc 

 can accelerate regenerative growth, and, by so 

 doing, can counteract the retarding effects of 

 methylmercury. In this species, the regeneration 

 rate of controls was similar in 30%o and 10%o sa- 

 linity, and the methylmercury retarded growth at 

 both salinities. This is in contrast to F. confluen- 

 tus in which decreased salinities depressed the 

 regeneration rate, thus masking the effects of 

 methylmercury in water of 9%o salinity (Weis and 

 Weis 1978). 



Methylmercury has previously been observed to 

 retard regeneration (Chang et al. 1976; Weis and 

 Weis 1978) and other developmental processes 

 (Chang et al. 1974). Its action as an inhibitor of 

 mitosis (Ramel 1969) could be the cause of these 

 effects on growth processes. As a potent nerve 

 poison it could further inhibit regenerative 

 growth by interfering with the neurotrophic 

 influence necessary for regeneration. 



Previous studies on the effects of zinc on grov^dh 

 include the work of Hirsch and Hurley (1978) in 

 which zinc was found to counteract the 

 teratogenic effects of 6-mercaptopurine in the rat. 

 They felt that the drug lowered DNA synthesis 

 and that the zinc counteracted this. Swenerton et 

 al. (1969) correlated zinc deficiency with reduced 

 DNA synthesis in rat embryos, and Falchuck et 

 al. (1975) have associated zinc with promoting cell 

 division in Euglena gracilis. Thus, if zinc can 

 promote DNA synthesis and cell division in fish 

 also, that would account for the observed acceler- 

 ation of regenerative growi:h. However, previous 

 studies on fish have not indicated such an effect. 

 Crandall and Goodnight (1962) reported that 1.15 

 ppm zinc retarded the growth of newborn gup- 

 pies. Rachlin and Perlmutter (1969) found that 18 

 ppm Zn reduced the mitotic index of cultured 

 rainbow trout, Salmo gairdneri, cells, but that 

 1.8-10.0 ppm had no effect on the mitotic index. 



On the other hand, zinc has often been found to 

 counteract toxic effects of other heavy metals. 

 Dixon and Compher (1977) found that zinc could 

 reverse a cadmium-caused inhibition of regenera- 

 tion in the nevft. Zinc has been found to coun- 

 teract the toxic effects of mercury in rats 

 (Yamane et al. 1977) and to counteract the 

 teratological effects of methylmercury in killifish 

 embryos (Weis et al. in press). 



In view of reports of fin rot of unknovvTi etiology 

 in flatfish from polluted environments (Ziskowski 



165 



