Page 90 - The Toxicology of Fishes

70 The Toxicology of Fishes

A 30

20 Direction of Change
% CHANGE FROM CONTROL -10 0
10

-20
-30
-40
-50
-60
7 8 9 10 11 12 13 14 15 16 17 18

B
30 Direction of Change
% CHANGE FROM CONTROL -10 0
20
10

-20
-30
-40
-50
-60
7 8 9 10 11 12 13 14 15 16 17 18
TEMPERATURE (°C)
FIGURE 3.6 Effect of temperature on branchial uptake of benzo(a)pyrene, 2,2′,5,5′-tetrachlorobiphenyl, and naphthalene
by rainbow trout. (A) Changes in chemical uptake efficiency (solid squares), oxygen uptake efficiency (solid circles),
chemical uptake rate (open squares), and oxygen consumption rate (open circles). (B) Changes in ventilation rate (solid
squares) and ventilation volume (solid circles). Each point represents the mean percentage change (±SE) from the control
value measured at the acclimation temperature, calculated by pooling data for all three compounds. (Adapted from Black,
M.C. et al., Physiol. Zool., 64, 145–168, 1991.)

and beyond the epithelial cells to the lamina propria, where vascular elements of the intestinal tract are
located. The lamina propria, besides providing a structural matrix supporting the mucosal epithelia,
serves as a storage and staging area for vascular transport of nutrients and associated xenobiotics.
Along the length of the GIT are regional differences in luminal pH, fluid fluxes, transporter systems,
enzymes, and enzymatic activities. Qualitatively, the digestive process in fish is similar to that of other
vertebrates. Quantitative differences exist, however, especially in relation to digestive enzyme concen-
trations and activities. Regional differences in these parameters, combined with structural differences,
restrict specific functions to more or less discrete locales. The regional nature of nutrient absorption is
one outcome of these differences. The residence time of a food bolus in any given part of the GIT
depends on many physical and physiological factors. In general, nutrient uptake and blood flows are
highly regionalized and respond to local stimuli initiated by the food bolus. As the food bolus moves
through the GIT, the character of the ingesta changes, as does the volume. Nutrients are absorbed and
mucus, bacteria, and epithelial cells are added. As a result, different regions of the absorptive surface
are presented with ingesta that differs in composition.