(X = 62.3 g). After the 96-hr exposure, eight of the ex- 
posed fish and four control fish were sacrificed to 
determine cadmium residues in various parts of the 
fish. The remaining eight cadmium-exposed fish and 
four control fish were placed in flowing seawater for 1 
mo, after which time they were sacrificed for cad- 
mium analysis. 
Sampling Procedures 
Uptake study.—For the uptake study, data were 
collected from three separate experiments, in each of 
which five different concentrations of cadmium were 
used, plus a control. A single pooled sample was made 
of the livers from four to five fish per exposure level. 
The same sampling procedure was followed with the 
gills, which were rinsed in clean seawater immediately 
after dissection to avoid possible adherence of cad- 
mium chloride to the gill surfaces. 
Clearance study.—Muscle, gills, liver, red blood 
cells, serum, and carcass were analyzed for cadmium 
residues. The sampling was as follows: 
Muscle.—Paired fillets were taken from each fish, 
skinned, and ground and combined into a single sam- 
ple per fish. The skin was added to the carcass sample 
(described below). 
Gill and liver.—Samples were taken as described 
above for the uptake study, except that the samples 
were analyzed individually. 
Red blood cells and serum.—Blood samples were 
pooled from four fish per treatment, except in the case 
of the cadmium-exposed fish held 1 mo in clean run- 
ning seawater; only seven fish survived, and their 
blood pools represented four and three fish, respec- 
tively. 
Whole blood was taken from the cunner by heart 
puncture, placed in a test tube, and allowed to clot at 
room temperature for 45-60 min. The serum was 
removed from the clot and centrifuged at 350-500 XG 
for 10 min. The clarified serum was frozen-stored until 
analysis. For the red blood cells samples, the cellular 
residue remaining after centrifugation was combined 
with the clot. 
Carcass.—The remainder of the fish after removal 
of the samples described above was called the carcass, 
and included the skin removed from the fillets. 
Chemical Analyses 
For analysis of cadmium in cunner tissues, samples 
were placed in 50-ml glass beakers, dried at 110°C for 
18 hr, and heated over a Bunsen burner to char the 
tissue. The samples were brought to 400°C in a muffle 
furnace, removed after 1 hr at that temperature, and 
cooled; a small amount of concentrated HNO, was 
added to wet the ash, and the samples were returned 
to the muffle furnace at room temperature and 
brought to 400°C again. This process was repeated 
until only a white residue remained in the beakers, 
usually after 3-5 additions of HNO;. The residue was 
rinsed from each beaker with 10% HNO, and filtered 
through Whatman” No. 2 paper. The filtrate was 
brought to a final 10-ml volume and subsequently 
analyzed with an atomic absorption spectrometer, 
employing a deuterium background corrector (Perkin 
Elmer? Model 403). 
RESULTS 
Uptake Study 
Cadmium accumulation was far greater in the liver 
than in the gills (Table 1). Cadmium concentrations 
averaged 8.2 (range 3-15) times higher in liver than in 
gill tissue for all concentrations tested. Although there 
was substantial variation in results for the three up- 
take experiments, the averaged data show a nearly 
linear relation for cadmium concentrations in liver 
versus cadmium exposure levels (Fig. 1). Variation in 
liver-cadmium concentration was greatest at 24 and 
48 ppm exposure levels, and least at 3, 6, and 12 ppm 
levels. 
Uptake of cadmium into gill tissues was curvilinear 
in form, as shown in a plot of cadmium concentrations 
in gills versus cadmium exposure levels (Fig. 2). Cad- 
mium concentrations in gill tissue for 3 and 6 ppm 
* Reference to trade names does not imply endorsement by the 
National Marine Fisheries Service, NOAA. 
0267 
200 
180 
160 
140 
120 
100 O Experiment 1 
& Experiment 2 
O Experiment 3 
@ Average of 1-3 
80 
60 
40 
20 
Cadmium Concentration In Livers(ppm,wet wt.) 
036 12 24 48 
Cadmium Concentration In Seawater (ppm) 
Figure 1.—Uptake of cadmium by the livers of cunner held 96 hr 
in various concentrations of cadmium (as cadmium chloride) in — 
artificial seawater. 
