creases in hematocrit were greater proportion- 

 ately: 23% and 45% of the control value in the 5 

 and 10 ppb-exposed groups. The greater 

 decrease in hematocrit represents not only a 

 lower number of red cells but, in addition, a 

 smaller mean volume in red cells of exposed ani- 

 mals, reflected in the significantly lower mean 

 corpuscular volume for exposed animals. 



Exposure to mercury also affected the osmo- 

 and ion-regulatory capacity of the striped bass 

 (Table 2). There was no significant difference be- 

 tween 5 ppb-exposed fish and controls in any of 

 the five plasma chemistry variables measured. 

 In the 10 ppb-exposed animals, the plasma 

 sodium and the osmolality increased to 238 

 mEq/1 and 462 mOsm. Plasma calcium dropped 

 to 3.98 mEq/1 in the 10 ppb-exposed group, 

 significantly lower than the control value of 4.52. 

 Although the mean calcium concentration in the 

 5 ppb-exposed fish was even lower, because of the 

 greater variability in that group, it was not 

 significantly different from that of controls. 

 There was no significant difference between 

 controls and 10-ppb-exposed fish in plasma pro- 

 tein or potassium. 



Table 2.— Effects of 60-d exposure to mercuric chloride on 

 plasma chemistry of striped bass (means ± SE with ranges in 

 parentheses). Plasma samples were pooled as necessary to ob- 

 tain volume of material required. 



"Significantly different from controls at 0.05 level, "Significantly dif- 

 ferent from controls at 0.001 level. 



Discussion 



Mercury had a major disruptive influence on 

 the hematology of the striped bass, affecting both 

 the red cell component of the blood and the 

 plasma chemistry. Mercury had similar effects 

 on winter flounder in an earlier study (Dawson 

 1979). In general, the changes demonstrated in 

 winter flounder paralleled those of striped bass 

 although the magnitude of change was smaller 

 in the winter flounder in spite of higher mercury 

 concentrations, namely, 10 and 20 ppb. The one 



exception was that the mean corpuscular volume 

 increased in winter flounder and decreased in 

 striped bass. The greater sensitivity to mercury 

 in striped bass may represent a real species dif- 

 ference or may simply reflect the smaller size of 

 the striped bass used. 



The alterations in plasma sodium and osmolal- 

 ity following mercury exposure may be caused 

 by gill-tissue damage. Meyer (1952) found de- 

 creased uptake and increased loss of sodium in 

 the gills of mercury-exposed goldfish in 

 freshwater. Olson et al. (1973) found ultrastruc- 

 tural damage in rainbow trout gills following 

 mercury exposure. Renfro et al. (1974) demon- 

 strated mercury uptake by the gill of the killifish, 

 Fundulus heteroclitus, in freshwater and con- 

 comitant inhibition of sodium uptake. Our labo- 

 ratory has demonstrated mercury uptake from 

 seawater into the gills of winter flounder (Cala- 

 brese et al. 1975). 



At least two sites of mercury accumulation 

 have been described which could account for 

 changes in the red cell component of the blood. 

 Olson et al. (1973) and Pentreath (1976) reported 

 the uptake of mercury into the blood of rainbow 

 trout and plaice which could lead to direct cell 

 damage. Perhaps more relevant are reports of 

 mercury accumulation in the kidneys of teleosts; 

 this would very likely affect renal hemopoiesis 

 and, hence, such variables as hematocrit, hemo- 

 globin, and RBC. Olson et al. (1973) reported a 

 high mercury concentration in the kidney 

 rainbow trout following a 24-h exposure. Pen- 

 treath (1976) reported that, following a 60-d 

 exposure of the plaice to 203 Hg, the kidney was 

 among the organs highest in 203 Hg. 



Hematology is a valuable tool for assessing a 

 variety of stresses in fish. Its main limitation lies 

 in the lack of information about the normal 

 range of values in fish. Wedemeyer and 

 Yasutake (1977) have noted that, in general, 

 hematological measurements show a greater 

 variation in fish than in many other animals. 

 Fish are subjected to a wide range of tempera- 

 ture, salinity, and nutrient availability, all of 

 which are likely to be reflected in their 

 hematology. Courtois (1976) has demonstrated 

 hematological changes in striped bass exposed to 

 varying conditions of temperature and salinity. 

 Bridges et al. (1976) have demonstrated signifi- 

 cant seasonal variation in winter flounder 

 hematology. Hesser (1960), Blaxhall and Daisley 

 (1973), and Wedemeyer and Yasutake (1977) 

 have attempted to standardize and interpret 



391 



