416
JAMES E. DEACON AND W. L. MINCKLEY
tern, and a maximum tolerance in nature of 40°C for C. nevadensis
calidae. One form of the Nevada pupfish now is known to move voluntarily
into waters of 42°C (Soltz and Brown, 1970). Desert pupfish from the
Salton Sea, California, (Barlow, 1958a) had thermal preferences similar
to those of C. n. calidae and were found holding territories at a maximum
of 38.3°C (Barlow, 1961b). A population of Cyprinodon at the Steinhart
aquarium was almost entirely killed when malfunction of an aquarium
heater raised the temperature to 43.3°C (Seale, in Miller, 1949b). It was
subsequently determined that C. macularius lived at 38.9°C, but would
exhibit marked discomfort and death at 40.6°C. Lowe and Heath (1969)
reported an experimental critical thermal maximum of 44.6°C for C.
macularius from Quitobaquito, Arizona, and found that form living in nature at about 41 °C.
The principal data on poeciliid fishes have been compiled for Gambusia
affinis, and its critical thermal maximum is near 40°C (Brett, 1956). At
Ojo Caliente, near Hermanas, Coahuila, Mexico, Gambusia marshi
avoided water at 41.5°C, occurred rarely along the banks at temperatures
of 40.5°C, seemed very hesitant to cross the channel (41 °C), but spread
to inhabit the entire flow at 40° =b 0.5°C. In the Cuatro Ciénegas basin
that species maintains a small population in Escobeda (36.7° ± 1°C), but
is very common in other springs that range from 17° to 35°C. The Escobeda population exhibits a high percentage of vertebral anomalies similar
to those reported by Hubbs (1959) for G. affinis in hot springs
(34.5°-35.5°C) of Big Bend National Park, Texas. In fluctuating habitats,
Gambusia marshi has been found highly emaciated and in small numbers
at temperatures of 43° to 44°C on one occasion. Otherwise the maximum temperatures recorded in this type of habitat where G. marshi was
present are near 39.5°C; this is the same maximum temperature at which
Hubbs (1959) found G. affinis.
Tolerances of some cyprinid species to high temperature may approach
those for cyprinodontoids. Some of the higher records are 39.5°C for red
shiner in New Mexico hot springs (Brues, 1928), 38°-40.5°C for
Eremichthys acros (desert dace) in Soldier Meadows, Nevada (Nyquist,
1963; Hubbs and Miller 1948b), 34°-36°C for Moapa coriacea in Moapa
Valley, Nevada (Hubbs and Miller, 1948b) and 36.8°C for adult longfin
dace in Arizona. Most minnow species have lower tolerances, in the range
of 30°-34°C, and these maxima seem typical for most other groups that
have been studied (Table I ) .
Acclimation to warm waters occurs much more rapidly than to cold
(Brett, 1956; Doudoroff, 1957), and thus it follows that heating is likely
to have less effect on survival than does rapid cooling. Few cases of natural
heat death of fishes have been recorded (Bailey, 1955; Norris, 1963; Lowe
JAMES E. DEACON AND W. L. MINCKLEY
tern, and a maximum tolerance in nature of 40°C for C. nevadensis
calidae. One form of the Nevada pupfish now is known to move voluntarily
into waters of 42°C (Soltz and Brown, 1970). Desert pupfish from the
Salton Sea, California, (Barlow, 1958a) had thermal preferences similar
to those of C. n. calidae and were found holding territories at a maximum
of 38.3°C (Barlow, 1961b). A population of Cyprinodon at the Steinhart
aquarium was almost entirely killed when malfunction of an aquarium
heater raised the temperature to 43.3°C (Seale, in Miller, 1949b). It was
subsequently determined that C. macularius lived at 38.9°C, but would
exhibit marked discomfort and death at 40.6°C. Lowe and Heath (1969)
reported an experimental critical thermal maximum of 44.6°C for C.
macularius from Quitobaquito, Arizona, and found that form living in nature at about 41 °C.
The principal data on poeciliid fishes have been compiled for Gambusia
affinis, and its critical thermal maximum is near 40°C (Brett, 1956). At
Ojo Caliente, near Hermanas, Coahuila, Mexico, Gambusia marshi
avoided water at 41.5°C, occurred rarely along the banks at temperatures
of 40.5°C, seemed very hesitant to cross the channel (41 °C), but spread
to inhabit the entire flow at 40° =b 0.5°C. In the Cuatro Ciénegas basin
that species maintains a small population in Escobeda (36.7° ± 1°C), but
is very common in other springs that range from 17° to 35°C. The Escobeda population exhibits a high percentage of vertebral anomalies similar
to those reported by Hubbs (1959) for G. affinis in hot springs
(34.5°-35.5°C) of Big Bend National Park, Texas. In fluctuating habitats,
Gambusia marshi has been found highly emaciated and in small numbers
at temperatures of 43° to 44°C on one occasion. Otherwise the maximum temperatures recorded in this type of habitat where G. marshi was
present are near 39.5°C; this is the same maximum temperature at which
Hubbs (1959) found G. affinis.
Tolerances of some cyprinid species to high temperature may approach
those for cyprinodontoids. Some of the higher records are 39.5°C for red
shiner in New Mexico hot springs (Brues, 1928), 38°-40.5°C for
Eremichthys acros (desert dace) in Soldier Meadows, Nevada (Nyquist,
1963; Hubbs and Miller 1948b), 34°-36°C for Moapa coriacea in Moapa
Valley, Nevada (Hubbs and Miller, 1948b) and 36.8°C for adult longfin
dace in Arizona. Most minnow species have lower tolerances, in the range
of 30°-34°C, and these maxima seem typical for most other groups that
have been studied (Table I ) .
Acclimation to warm waters occurs much more rapidly than to cold
(Brett, 1956; Doudoroff, 1957), and thus it follows that heating is likely
to have less effect on survival than does rapid cooling. Few cases of natural
heat death of fishes have been recorded (Bailey, 1955; Norris, 1963; Lowe