448
JAMES E. DEACON AND W. L. MINCKLEY
active during the warmest time of day. They avoided cooler waters and
were inactive at night. Selection of the warmest available water was clearly
occurring in this instance since population movement of about 40 meters
was required for them to remain in the warmest water and to avoid the
coolest. Gila mohavensis in the same pool usually exhibited an opposite
response to temperature, always occupying the coolest water available.
Longfin dace also perform movements in response to environmental
temperatures, and the complexity of stream environments provides a fertile
area for investigation of such behavior. When flowing water approximately
1 cm deep was 36.8°C in the center of Sycamore Creek, Arizona, temperatures in slightly deeper places adjacent to algal mats were 33.1°-34.2°C,
and in a quiet place near an overhanging tree, 30.4°C was recorded. Adult
dace all were concentrated in shade of the tree. Juveniles were generally
distributed along the banks, darting occasionally across the warmer channel. At water temperatures between 30° and 33°C, most dace were active
throughout the creek (and at those temperatures in Aravaipa and Sonita
creeks on other dates as well).
Low temperatures may also elicit behavioral responses in desert fishes.
Thermal preferentia of Cyprinodon macularius in the Salton Sea in winter
ranged from a low of about 8°C in early morning to about 20°C in midafternoon (Barlow, 1958a). Winter activity of Nevada pupfish in the
marsh associated with Saratoga Springs occurs only when temperatures exceed 10° to 12°C. In Cuatro Ciénegas, C. atrorus becomes active between
7° and 9°C. Individuals of C. n. nevadensis lose equilibrium at 5°-6°C,
and can move only in violent, erratic paths. Only weak, uncoordinated,
swimming movements were possible in the last species at experimental temperatures of about 2.8°C. Temperatures lower than about 7°C completely
preclude activity in undisturbed pupfishes studied by us in nature. All typically burrow in the substrate or seek cover beneath debris, and remain
inactive there until temperatures increase. The report by Cox (1966) of
total dormancy of pupfish at Quitobaquito from October to April at temperatures varying up to 19.8°C is in error, according to our data recorded
for that population over a number of years.
Burrowing by Cyprinodon occurs at any time, often in response to disturbance, but it may also be a means of avoiding temperature extremes from
which other forms of escape are impossible. At low temperatures the fish
must burrow actively (as has frequently been observed) into the soft bottom prior to becoming immobilized. The mud doubtless provides both thermal insulation and protective cover, and potential metabolic advantages
of residence in anaerobic muds may be quite high (Blazka, 1958; Eckberg,
1962). Some pupfish confined in cages at Saratoga Marsh, Death Valley,
burrowed without artificial disturbance. Water temperatures ranged from
JAMES E. DEACON AND W. L. MINCKLEY
active during the warmest time of day. They avoided cooler waters and
were inactive at night. Selection of the warmest available water was clearly
occurring in this instance since population movement of about 40 meters
was required for them to remain in the warmest water and to avoid the
coolest. Gila mohavensis in the same pool usually exhibited an opposite
response to temperature, always occupying the coolest water available.
Longfin dace also perform movements in response to environmental
temperatures, and the complexity of stream environments provides a fertile
area for investigation of such behavior. When flowing water approximately
1 cm deep was 36.8°C in the center of Sycamore Creek, Arizona, temperatures in slightly deeper places adjacent to algal mats were 33.1°-34.2°C,
and in a quiet place near an overhanging tree, 30.4°C was recorded. Adult
dace all were concentrated in shade of the tree. Juveniles were generally
distributed along the banks, darting occasionally across the warmer channel. At water temperatures between 30° and 33°C, most dace were active
throughout the creek (and at those temperatures in Aravaipa and Sonita
creeks on other dates as well).
Low temperatures may also elicit behavioral responses in desert fishes.
Thermal preferentia of Cyprinodon macularius in the Salton Sea in winter
ranged from a low of about 8°C in early morning to about 20°C in midafternoon (Barlow, 1958a). Winter activity of Nevada pupfish in the
marsh associated with Saratoga Springs occurs only when temperatures exceed 10° to 12°C. In Cuatro Ciénegas, C. atrorus becomes active between
7° and 9°C. Individuals of C. n. nevadensis lose equilibrium at 5°-6°C,
and can move only in violent, erratic paths. Only weak, uncoordinated,
swimming movements were possible in the last species at experimental temperatures of about 2.8°C. Temperatures lower than about 7°C completely
preclude activity in undisturbed pupfishes studied by us in nature. All typically burrow in the substrate or seek cover beneath debris, and remain
inactive there until temperatures increase. The report by Cox (1966) of
total dormancy of pupfish at Quitobaquito from October to April at temperatures varying up to 19.8°C is in error, according to our data recorded
for that population over a number of years.
Burrowing by Cyprinodon occurs at any time, often in response to disturbance, but it may also be a means of avoiding temperature extremes from
which other forms of escape are impossible. At low temperatures the fish
must burrow actively (as has frequently been observed) into the soft bottom prior to becoming immobilized. The mud doubtless provides both thermal insulation and protective cover, and potential metabolic advantages
of residence in anaerobic muds may be quite high (Blazka, 1958; Eckberg,
1962). Some pupfish confined in cages at Saratoga Marsh, Death Valley,
burrowed without artificial disturbance. Water temperatures ranged from