FISHERY BULLETIN: VOL. 75, NO. 1 



chemical analyses were performed to determine 

 the cadmium uptake of certain tissues. 



METHODS AND MATERIALS 



Cunners for this study were trap-collected in 

 Long Island Sound near Milford, Conn., during the 

 summer of 1974 and held in the laboratory for 1 to 

 2 wk in flowing, sand-filtered seawater prior to 

 cadmium exposure. They were fed Purina Trout 

 Chow 2 throughout the holding and exposure 

 periods. Beginning in August and ending in 

 October 1974, the cunners were exposed in aer- 

 ated, 285-liter fiber glass tanks filled to 228 liters 

 with sand-filtered seawater (24±2%o salinity, 

 22±2°C) by a proportional-dilution apparatus 

 (Mount and Brungs 1967). This diluter controlled 

 the intermittent delivery of toxicant-containing 

 water to each tank throughout the exposure period 

 at a flow rate of 1.5 liters every 2.5 min. This flow 

 rate provided approximately four complete ex- 

 changes of water daily in each tank. Cadmium was 

 added as CdCb ■2 1 /2H20 at concentrations of 0.05 

 and 0.10 ppm Cd. Background level of cadmium in 

 the seawater was less than 0.001 ppm. Four tanks 

 were used per concentration and control, with 15 

 fish in each tank, for a total of 60 fish per test level. 

 The fish averaged 55.7 g in weight (range, 32.5- 

 96.9 g) and 157 mm total length (range, 133-185 

 mm). After 30- and 60-day exposure periods, fish 

 were removed for testing. 



For oxygen-consumption measurements, two 

 gills were dissected from each fish and placed in a 

 15-ml Warburg-type flask containing 5 ml water 

 from the corresponding experimental tank. Oxy- 

 gen consumption was monitored over a 4-h period 

 at 20°C in a Gilson Differential Respirometer with 

 a shaking speed of 80 cycles/min. Rates of oxygen 

 uptake were calculated as microliters of oxygen 

 consumed per hour per gram dry weight gill tissue 

 (/a1 02/hg), including the gill arch, corrected to 

 microliters of dry gas at standard temperature and 

 pressure. 



Liver tissue was taken for enzyme testing. Pools 

 comprising liver samples from two fish were 

 placed in small plastic pouches from which air was 

 subsequently excluded, then sealed and stored 

 frozen at -29°C. No more than 2 wk elapsed 

 between the end of the exposure period and test- 

 ing, as both AAT and G6PdH have been found to 



lose some activity after a month's frozen storage of 

 whole liver tissue. For testing, each liver sample 

 was homogenized 1:9, wt/vol, with iced, doubly 

 glass-distilled water in a small, conical-tip glass 

 homogenizer containing 25-/xm glass powder to 

 facilitate grinding. Centrifugation was at 17,000 g 

 and 4°C for 45 min. The supernatant fractions 

 were removed with Pasteur pipettes, diluted 1:1.5 

 with the iced water, vol/vol, and recentrifuged 

 under the same conditions. The resulting 

 supernates served as the 4% liver preparations. 

 Protein determinations were made by the biuret 

 method (Gornal et al. 1949), with modifications by 

 Layne (1957), using a crystallized bovine serum 

 albumin standard. The coupled spectrophotomet- 

 ric assay for AAT was the same as that used in the 

 acute, short-term exposure of cunners to cadmium 

 described by Gould and Karolus (1974). For 

 G6PdH, both assay medium and spectro- 

 photometric procedures have also been described 

 elsewhere (Gould in press). Unit of activity was 

 micromoles NADH oxidized (AAT) or NADP 

 reduced (G6PdH) per minute per milligram 

 protein. 



Gill, muscle, and liver tissues were analyzed for 

 cadmium uptake using the method described by 

 Greig et al. (1975), in which the samples were 

 wet-ashed with concentrated HNO3, taken up in 

 10% HNO3, and analyzed directly by atomic 

 absorption spectrophotometry. Values were 

 calculated on a wet-weight basis. 



RESULTS AND DISCUSSION 



Mortality and Respiration 



Table 1 shows the actual and adjusted mortality 

 data after 30- and 60-day exposures. Mortality 

 data for the exposed fish were corrected for natural 

 mortality of the controls by using Abbott's formula 

 (Finney 1971), and can be interpreted as wholly 

 attributable to cadmium stress. Clearly, exposure 

 to low levels of cadmium increased the incidence of 

 mortality, more so at 0.1 ppm than at 0.05 ppm. 



TABLE 1. — Actual and adjusted percent mortality of cadmium- 

 exposed cunner, Tautogolabrus adspersus. 



2 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



'Adjustments made by Abbott's formula (Finney 1971). 

 2 Number dead out of 60 fish. 



200 



