MacINNES ET AL.: LONG-TERM CADMIUM STRESS IN THE CUNNER 



TABLE 2. — Gill-tissue oxygen consumption rates of cadmium-exposed cunner, 



Tautogolabrus adspersus. 



Exposure 



concentration 



(ppm Cd) 



30 days: 



0.00 



0.05 



0.10 

 60 days: 



0.00 



0.05 



0.10 



Number 

 of 

 fish 



Oxygen consumption rates' 

 X SE Range 



Level of 

 significance 2 



>■ 005 "I 

 NS J 



] 

 ] 



P 0.01 

 NS 



'Microliters O; per hour per gram dry weight. 

 2 Students f-test. 



P- 0.025 



P<0.005 



Gill-tissue oxygen consumption was sig- 

 nificantly reduced after both 30- and 60-day 

 exposures to 0.05 and 0.10 ppm Cd (Table 2), a 

 result similar to that reported by Thurberg and 

 Dawson (1974) in cunners exposed to 3 ppm Cd for 

 96 h. The depression was more pronounced at the 

 end of the 60-day than at the end of the 30-day 

 exposure. In another chronic exposure study, 

 Dawson et al. (in press) found that gills of juvenile 

 striped bass, Morone saxatilis, exposed to 0.5, 2.5, 

 or 5.0 ppb Cd for 30 and 90 days, consumed sig- 

 nificantly less oxygen than did the controls. The 

 concentrations used were less than one-tenth of 

 those used in the present study, but they still 

 produced significant respiratory changes. The 

 results reported here are also supported by a study 

 using the winter flounder (Calabrese et al. 1975), 

 in which fish exposed to 5 or 10 ppb Cd for 60 days 

 showed significantly reduced oxygen consumption 

 rates. 



Exposure to silver also depresses cunner gill- 

 tissue respiration (Thurberg and Collier in press). 

 There is some evidence, however, that other met- 

 als affect fish respiration differently. Cunners 

 exposed to 5 or 10 ppb mercury (as HgCh) for 30 

 and 60 days had significantly elevated respiration 

 rates after 30 days, but normal respiration after 60 

 days (unpubl. data). Similarly opposite effects of 



the two metals, mercury and cadmium, were 

 reported for the winter flounder in 60-day expo- 

 sure studies (Calabrese et al. 1975); i.e., mercury 

 elevated the oxygen consumption rate, whereas 

 cadmium lowered it. 



Enzyme Activity 



In the liver of cunners exposed for 30 days to 0.1 

 ppm cadmium as chloride, AAT activity was 

 significantly lower (P<0.02) than in control fish 

 (Table 3). The drop in activity, about 20%, cor- 

 roborates the effect of cadmium on liver AAT 

 observed in cunners exposed for 4 days to high 

 concentrations (24 ppm Cd) of this metal salt 

 (Gould and Karolus 1974). As is the case with all 

 aminotransferases, pyridoxal phosphate is an 

 absolute requirement for activity. Because the 

 biosynthesis of this essential cofactor requires a 

 divalent metal cation (Meister 1955), and because 

 cadmium affects enzymes requiring or reacting 

 with divalent metal cations (Gould in press), it 

 seems probable that cadmium's inhibitory effect 

 on AAT activity is at the point of pyridoxal 

 phosphate synthesis. 



Liver G6PdH in cunners exposed for 30 days to 

 0.05 ppm Cd was significantly higher (P<0.05) 

 than in controls (Table 3), and at 0.1 ppm the 



TABLE 3. — Aspartate aminotransferase and glucose-6-phosphate dehydrogenase in 

 the liver of cunner, Tautogolabrus adspersus, exposed for 30 days to cadmium 

 chloride. 



201 



