FISHERY BULLETIN: VOL. 71, NO. 1 



concentrations in water of 10, 20, and 30%r sa- 

 linity maintained at 10°, 20°, or 30°C. Each 

 experimental group had a control maintained in 

 uncontaminated water, but subjected to the sa- 

 linity and temperature stresses. 



Cadmium concentrations in the tissues of 

 crabs exposed to lethal concentrations were de- 

 termined by use of radioactive cadmium (^"''Cd) 

 using the following procedure. Fifteen male and 

 15 female crabs were placed in 300 ml of filtered 

 seawater of 20^f salinity at 30°C. Each of three 

 test chambers received 2.3 fxc '"^Cd and an aliquot 

 of stock soultion to bring the cadmium level to 

 5, 15, or 25 ppm Cd"^"^. These thermosaline 

 regimes and cadmium concentrations were 

 chosen because the acute toxicity tests show that 

 they cause relatively high mortality rates. Four 

 active animals (two males, two females) were 

 sacrificed from each chamber at 0, 12, 24, 36, 48, 

 and 60 hr. The animals were frozen until dis- 

 section of the tissues could be accomplished. 

 Four tissues were digested and analyzed: he- 

 patopancreas, gill, green gland, and thoracic 

 muscle. Individual crabs were analyzed; since 

 results from males and females showed no mea- 

 surable difference, the results were pooled. Con- 

 centrations of ^"^Cd were determined by liquid 

 scintillation on a Packard Tricarb Model 3320 

 counter." Since each 2.3 /uc represented 1.5, 4.5, 

 or 7.5 mg of cadmium in the test water, a simple 

 ratio of counts per minute to microgram of cad- 

 mium was determined from spiked samples and 

 used to calculate the amount of cadmium in the 

 tissues. Concentrations of cadmium are ex- 

 pressed as parts per million wet weight of tissue. 



RESULTS 



Table 1. — Cadmium concentrations (Cd ''■■'" in ppm) lethal 

 to 50% of test organisms (TLm) at different salinities, 

 times, and temperatures. 



regime of 30°C and lO^r. The concentration 

 fatal to 50% of the organisms in 240 hr (TLm- 

 240 hr) was calculated to be 2.9 ppm Cd*"^ 

 (American Public Health Association, 1971). 

 At higher cadmium concentrations, the time re- 

 quired to kill 50% of the crabs was considerably 

 reduced. 



Table 1 shows the influence of temperature, 

 salinity, and cadmium concentration on the level 

 of toxicant which kills 50% of the crabs in dif- 

 ferent time periods. The effect of temperature 

 was extremely pronounced and TLm values were 

 generally more influenced by temperature 

 changes than by salinity levels within a thermal 

 regime. The influence of salinity on the TLm- 

 240 hr was most pronounced at 10°C and 10%c 

 and at higher cadmium concentrations in shorter 

 times. The combined role of temperature and 

 salinity on cadmium toxicity indicates that tem- 

 perature is less influential at higher salinities. 



ACUTE TOXICITY 



In general, the higher temperatures and lower 

 salinities produced the greatest cadmium tox- 

 icity. The susceptibility of fiddler crabs to cad- 

 mium was most pronounced in the thermosaline 



^ Reference to trade names in the publication does 

 not imply endorsement of commercial products by the 

 National Marine Fisheries Service, NOAA. 



TISSUE ACCUMULATION 



Gills 



In the first 12 hr of exposure, gill tissue ac- 

 cumulated cadmium in proportion to the ex- 

 posure concentration (Figure 1). Thus, gill 

 tissue from crabs exposed to 25 ppm Cd"""" con- 

 tained 110 ppm; gill tissue from those exposed 



150 



