VII. DESERT FISHES
419
Arizona, air temperature may change as much as 30°C from day to night
in spring and autumn, especially where drain of colder, montane air flows
down canyons at night. In summer, variation is of a lesser magnitude, perhaps 15°-20°C, overall, and this also is true in winter ranging from 4°
to 10°C at night to 25°C in the day (Green and Sellers, 1964). Water
temperatures tend to change more slowly but nevertheless fluctuate over
a similar range.
Maximum diel variations recorded in small pools of Cuatro Ciénegas
basin have been 13°-31°C in April, 24°-44°C in August, and 1.3°-18.5°C
in December. Cooler temperatures are achieved, as witnessed by formation
of ice that will hold the weight of a man (Minckley, 1969b), and water
as hot as 53°C has been found in almost azoic, salt-encrusted pools in
summer. Comparable data in Death Valley waters include maximum diel
variations of 27°-42°C in the marsh at Saratoga Springs in July,
13.9°-25°C in March, and 4°-20°C in December. Since these temperatures
were taken in open water, greater daily ranges are to be expected in the
shallower parts of the marsh. The most extreme thermal variations in fish
habitats of Death Valley probably occur in Cottonball Marsh where temperature data unfortunately have not been taken. Barlow (1958a) reported
diel temperature ranges of as much as 20°C in shore pools of the Salton
Sea, quite comparable to those in Death Valley and Cuatro Ciénegas, but
ranging only to a maximum of 38.7°C. Lowe and Heath (1969) report
diel ranges of 22°-26°C in shallow waters of Quitobaquito Spring, Arizona, to a maximum of 41 °C.
Intermittent pools in creeks have similar ranges in temperature, but
flowing waters are typically less extreme. Maximum diel ranges of 20°C
occur in Sycamore Creek, Arizona, to a maximum of about 40.3°C; however, adult fishes have not been recorded at temperatures higher than
36.8°C. Temperature relations in small streams are highly complex, as detailed earlier (Section ΙΙ,Α). Volume of flow in large rivers, plus other
factors, tends to reduce variability.
Under conditions of summer extremes the period of potential recovery
and repair during cooler times may be highly significant to desert fishes.
Some insight into biochemical mechanisms involved in such repair periods
is provided by Baslow (1967). Biochemical changes occur first in the
brain, and then elsewhere, in fishes subjected to thermal stress. Biochemical
equilibrium to new thermal environments is attained only after several days
or weeks, and involves changes in levels of amino acids and enzymes to
accomplish acclimation. A cyclical daily regime apparently permits more
gradual, and therefore biochemically more satisfactory, adjustment than is
possible under sudden exposure to markedly different thermal conditions.
Initial reactions in the central nervous system appear a few hours after
419
Arizona, air temperature may change as much as 30°C from day to night
in spring and autumn, especially where drain of colder, montane air flows
down canyons at night. In summer, variation is of a lesser magnitude, perhaps 15°-20°C, overall, and this also is true in winter ranging from 4°
to 10°C at night to 25°C in the day (Green and Sellers, 1964). Water
temperatures tend to change more slowly but nevertheless fluctuate over
a similar range.
Maximum diel variations recorded in small pools of Cuatro Ciénegas
basin have been 13°-31°C in April, 24°-44°C in August, and 1.3°-18.5°C
in December. Cooler temperatures are achieved, as witnessed by formation
of ice that will hold the weight of a man (Minckley, 1969b), and water
as hot as 53°C has been found in almost azoic, salt-encrusted pools in
summer. Comparable data in Death Valley waters include maximum diel
variations of 27°-42°C in the marsh at Saratoga Springs in July,
13.9°-25°C in March, and 4°-20°C in December. Since these temperatures
were taken in open water, greater daily ranges are to be expected in the
shallower parts of the marsh. The most extreme thermal variations in fish
habitats of Death Valley probably occur in Cottonball Marsh where temperature data unfortunately have not been taken. Barlow (1958a) reported
diel temperature ranges of as much as 20°C in shore pools of the Salton
Sea, quite comparable to those in Death Valley and Cuatro Ciénegas, but
ranging only to a maximum of 38.7°C. Lowe and Heath (1969) report
diel ranges of 22°-26°C in shallow waters of Quitobaquito Spring, Arizona, to a maximum of 41 °C.
Intermittent pools in creeks have similar ranges in temperature, but
flowing waters are typically less extreme. Maximum diel ranges of 20°C
occur in Sycamore Creek, Arizona, to a maximum of about 40.3°C; however, adult fishes have not been recorded at temperatures higher than
36.8°C. Temperature relations in small streams are highly complex, as detailed earlier (Section ΙΙ,Α). Volume of flow in large rivers, plus other
factors, tends to reduce variability.
Under conditions of summer extremes the period of potential recovery
and repair during cooler times may be highly significant to desert fishes.
Some insight into biochemical mechanisms involved in such repair periods
is provided by Baslow (1967). Biochemical changes occur first in the
brain, and then elsewhere, in fishes subjected to thermal stress. Biochemical
equilibrium to new thermal environments is attained only after several days
or weeks, and involves changes in levels of amino acids and enzymes to
accomplish acclimation. A cyclical daily regime apparently permits more
gradual, and therefore biochemically more satisfactory, adjustment than is
possible under sudden exposure to markedly different thermal conditions.
Initial reactions in the central nervous system appear a few hours after