were exposed in 80 1 glass aquaria filled to 60 1 

 with sand-filtered seawater by a proportional- 

 dilution apparatus (Mount and Brungs 1967). 

 The dilutor controlled the intermittent delivery 

 of mercury-treated and control water at a flow 

 rate of 1 1 to each tank every 3 min throughout the 

 test period. This provided a flow of 480 1/tank 

 per d and an estimated 90% replacement time of 

 7 h (Sprague 1969). Mercury, as mercuric 

 chloride, was added at concentrations of 5 and 10 

 ppb. The concentrations are nominal concentra- 

 tions of the metal ion in solution, not including 

 the background level, which was below 0.3 ppb. 

 The fish were exposed for 60 d and then removed 

 for testing. Each tank contained 5 fish, for a total 

 of 15 fish at each mercury concentration and 15 

 controls. The fish averaged 17.1 cm long (range 

 13.1-19.0) and 59.3 g (range 22.7-79.3). The expo- 

 sure ran from late November 1976 to January 

 1977. The temperature ranged from a high of 

 8°C at the beginning of the exposure period to a 

 low of 0°C at the termination of the exposure. 

 Salinity during the exposure period averaged 

 27.07.. and ranged from 26.0 to 29.67.. with the 

 exception of 1 d when it fell to 207... 



Hematology 



Blood was collected from each fish by cardiac 

 puncture using a 3 ml plastic syringe and a 22- 

 gage needle. The sample was transferred gently 

 into an 8 ml glass vial containing 150 units of 

 dried ammonium heparinate as an anticoagu- 

 lant. Microhematocrits (packed red cell vol- 

 umes) were determined following centrifugation 

 for 5 min at 13,500 X g. Hemoglobin concentra- 

 tions were determined by the cyanmethemoglo- 

 bin method using the Hycel reagent; absorbance 

 was read on a Bausch and Lomb Spectronic 20 

 spectrophotometer at 540 nm. Erythrocytes 

 were counted in a hemacytometer using Natt- 

 Herricks diluting fluid (Natt and Herrick 1952) 

 at a 1:200 dilution. Within 4 h after collection, 

 the remaining blood sample was centrifuged at 

 12,000 X g for 4 min and the plasma frozen for 

 later determination of osmolality, protein, 

 sodium, potassium, and calcium. Plasma 

 sodium, potassium, and calcium concentrations 

 were measured with a Coleman 51 flame photo- 

 meter. Plasma protein was determined by the 

 Biuret method as modified by Layne (1957). 

 Plasma osmolalities were determined on an 

 Advanced 3L osmometer using a 0.2 ml sample. 

 Samples were pooled as necessary to obtain a 0.2 



ml volume. The effect of the added heparin on the 

 osmolality was negiligible. Three indices were 

 computed from the measured values: mean 

 corpuscular volume in cubic micrometers/cell = 

 Hct/RBC X 10, mean corpuscular hemoglobin in 

 picograms/cell = Hb/RBC X 10, and mean 

 corpuscular hemoglobin concentration in grams/ 

 100 ml packed red cells = Hb/Hct X 100. All data 

 were analyzed using Student's t-test. 



Results 



Control fish had a mean hematocrit of 47%, a 

 hemoglobin concentration of 8.7 g/100 ml, and a 

 red cell count of 4.10 X 10 6 cells/mm 3 (Table 1). 

 These values resemble those reported by other 

 investigators: Courtois (1976), using striped bass 

 of similar size acclimated to cold seawater, re- 

 ported a mean hematocrit of 46 and a hemo- 

 globin of 8.4. More recently, Westin (1978) 

 reported a hematocrit of 47.9, a hemoglobin of 

 9.11, and a red cell count of 3.79 for adult striped 

 bass during the spawning season. 



The effects of mercury on the erythrocyte 

 component of the blood were pronounced (Table 

 1). Hematocrit, hemoglobin, and RBC all 

 decreased following mercury exposure. In each 

 case the response was significantly greater at the 

 higher mercury concentration. The reduction in 

 hemoglobin was proportional to the reduction in 

 red cell count: About 10% in the 5 ppb-exposed 

 animals and about 25% in the 10 ppb-exposed 

 animals. This is reflected in the lack of change of 

 the mean corpuscular hemoglobin and indicates 

 that the lowered hemoglobin concentration in 

 exposed fish is the result of a lower number of 

 circulating erythrocytes and not of a smaller 

 quantity of hemoglobin in each cell. The de- 



Table 1.— Effects of 60-d exposure to mercuric chloride on 

 erythrocytes of striped bass (means ± SE with ranges in 

 parentheses). 



"Significantly different from controls at 0.005 level, '"Significantly dif- 

 ferent from controls at 0.001 level. 



390 



