Page 88 - The Toxicology of Fishes

68 The Toxicology of Fishes

A
100 400

Endrin Uptake Ventilation 300
UPTAKE EFFICIENCY (%) 50 Oxygen Uptake Volume 200 VENTILATION VOLUME (mL/min)
75

100
25

0 0
100 80 50 30 0

B
35 High Endrin
ENDRIN UPTAKE (µg/kg day) 25 Low Endrin
30

20

15
10
5
0
100 80 50 30 0
DISSOLVED OXYGEN (% saturation)

FIGURE 3.5 Effect of dissolved oxygen concentration on branchial uptake of endrin by brook trout. (A) Changes in
ventilation volume, oxygen uptake efficiency, and endrin uptake efficiency. (B) Changes in endrin uptake rate at high (0.072
mg/L) and low (0.046 mg/L) waterborne concentrations. (Adapted from McKim, J.M. and Goeden, H.M., Comp. Biochem.
Physiol., 72C, 65–74., 1982.)

Complicating these comparisons, however, is the issue of fish size. For small fish, such as the guppy,
dermal absorption may account for up to 50% of total uptake of waterborne chemicals with high log
K values (Lien and McKim, 1993). Assuming that skin perfusion as a fraction of cardiac output remains
ow
constant, chemical absorption across the skin would change very little with a decrease in the oxygen
content of water, reducing the overall effect of any change in oxygen content on total chemical uptake.
Temperature—Environmental temperature changes can cause dramatic changes in the metabolic rates
of poikilothermic animals (Prosser, 1973), which affects their demand for oxygen. An increase in oxygen
demand due to increased temperature is especially problematic because the solubility of oxygen in water
is inversely related to temperature. To obtain more or less oxygen, a fish in most cases adjusts its
ventilation volume and the number of perfused lamellae in contact with respiratory water (Randall,
1982). This suggests that, if chemical uptake was controlled by water flow across the gills, an increase
in temperature would increase branchial uptake rate in a manner qualitatively similar to that of a decrease
in oxygen content. Changes in temperature also affect cardiac output and could potentially impact
branchial absorption if blood flow to the gills was a limiting factor. Several authors have investigated
the relationship between chemical uptake and oxygen consumption at different water temperatures. Using
rainbow trout, Rodgers and Beamish (1981) reported that branchial uptake of methylmercury was