414
JAMES E. DEACON AND W. L. MINCKLEY
known for the genus (LaBounty, 1968; LaBounty and Deacon, 1971).
Cyprinodon atrorus in the Cuatro Ciénegas basin behaves similarly in small
pools where gypsum crystals form outward from the sides, but they more
frequently remain near or within dense clumps of Chara that persist in
the center of desiccating pools. Temperatures within such clumps are as
much as 5°C lower than surface temperatures at midday in spring and
winter; unfortunately, no summer temperatures have been recorded. Fox
(1926) similarly reported close association of Cyprinodon ( = Aphanius)
dispar with beds of algae in salt pools at Kabret.
Great differentials in temperature may also occur in flowing creeks. In
tributaries of the Red River in northern Texas, Cyprinodon rubrofluviatilis
was concentrated in shade of a bridge at 11 A.M. in April, 1964, water
temperature in the channel was 34.8°C, and in their immediate vicinity
30°C; Gambusia affinis and Fundulus kansae both remained in the channel
or along banks near debris. In Sycamore Creek, Arizona, temperature variations commonly exceed 12°C in different habitats at a given moment in
summer, at depths ranging from 0.5 cm to slightly more than 5.0 cm. Deep
pools stratify strongly in Fish Creek, Arizona, with surface temperatures
of 29°C contrasting with 18°C at depths of only 1 meter; downstream,
0.5 km below the canyon, surface temperatures in riffles were as high as
31.5°C in August 1965.
Chemical stratifications may also occur when saline water fails to mix
with fresh water that flows over it. The saline lens may then accumulate
heat retained because of the overlying stratum that inhibits evaporative
cooling. Beadle (1943) recorded this phenomenon in Algerian pools, Cole
et al. (1967) in Arizona, and Cole and Minckley (1968) in Coahuila,
Mexico. To encounter such circumstances is a remarkable experience.
In the Mexican instance, surface water was 24°C and numerous fishes were
evident. Minckley stepped into the first of two pools, then quickly retreated
when bottom water (about 48 cm deep) of 45°C was encountered by
his sneaker-clad feet. Temperature in a second, undisturbed pool was 24°C
at the surface (total dissolved solids 14.63 gm/liter; specific gravity at environmental conditions, 1.01) and 47°C at the bottom (total dissolved
solids 111.26 gm/liter; specific gravity 1.075) (Cole and Minckley,
1968). Fishes conspicuously avoided the warm stratum, hiding along the
banks when disturbed.
One of the warmer records for fishes in North America is that of the
spring from which Lucania browni ( = Cyprinodon macularius) was described from northeastern Baja California (Jordan and Richardson, 1907).
The temperature of 48.9°C was taken with a standardized instrument by
highly trained personnel (Miller, 1948, 1949b), and has not, to our knowledge, again been checked, unless the spring visited by Kniffin (1932) was
JAMES E. DEACON AND W. L. MINCKLEY
known for the genus (LaBounty, 1968; LaBounty and Deacon, 1971).
Cyprinodon atrorus in the Cuatro Ciénegas basin behaves similarly in small
pools where gypsum crystals form outward from the sides, but they more
frequently remain near or within dense clumps of Chara that persist in
the center of desiccating pools. Temperatures within such clumps are as
much as 5°C lower than surface temperatures at midday in spring and
winter; unfortunately, no summer temperatures have been recorded. Fox
(1926) similarly reported close association of Cyprinodon ( = Aphanius)
dispar with beds of algae in salt pools at Kabret.
Great differentials in temperature may also occur in flowing creeks. In
tributaries of the Red River in northern Texas, Cyprinodon rubrofluviatilis
was concentrated in shade of a bridge at 11 A.M. in April, 1964, water
temperature in the channel was 34.8°C, and in their immediate vicinity
30°C; Gambusia affinis and Fundulus kansae both remained in the channel
or along banks near debris. In Sycamore Creek, Arizona, temperature variations commonly exceed 12°C in different habitats at a given moment in
summer, at depths ranging from 0.5 cm to slightly more than 5.0 cm. Deep
pools stratify strongly in Fish Creek, Arizona, with surface temperatures
of 29°C contrasting with 18°C at depths of only 1 meter; downstream,
0.5 km below the canyon, surface temperatures in riffles were as high as
31.5°C in August 1965.
Chemical stratifications may also occur when saline water fails to mix
with fresh water that flows over it. The saline lens may then accumulate
heat retained because of the overlying stratum that inhibits evaporative
cooling. Beadle (1943) recorded this phenomenon in Algerian pools, Cole
et al. (1967) in Arizona, and Cole and Minckley (1968) in Coahuila,
Mexico. To encounter such circumstances is a remarkable experience.
In the Mexican instance, surface water was 24°C and numerous fishes were
evident. Minckley stepped into the first of two pools, then quickly retreated
when bottom water (about 48 cm deep) of 45°C was encountered by
his sneaker-clad feet. Temperature in a second, undisturbed pool was 24°C
at the surface (total dissolved solids 14.63 gm/liter; specific gravity at environmental conditions, 1.01) and 47°C at the bottom (total dissolved
solids 111.26 gm/liter; specific gravity 1.075) (Cole and Minckley,
1968). Fishes conspicuously avoided the warm stratum, hiding along the
banks when disturbed.
One of the warmer records for fishes in North America is that of the
spring from which Lucania browni ( = Cyprinodon macularius) was described from northeastern Baja California (Jordan and Richardson, 1907).
The temperature of 48.9°C was taken with a standardized instrument by
highly trained personnel (Miller, 1948, 1949b), and has not, to our knowledge, again been checked, unless the spring visited by Kniffin (1932) was