420
JAMES E. DEACON AND W. L MINCKLEY
application of stress. The relatively brief exposure to thermal stress at midday doubtless results in similar phenomena that are rectified at times of
more hospitable conditions.
Probably significantly related to the above mechanism is the observation
by Schlieper et al. (1952) that brown trout and Planaria alpina survive
longer at lethal temperatures and show a reduction in the rate of increase
of respiration as temperature increases when much Ca
2+
is added to the
medium. As temperatures of desert pools increase in the summer, evaporation usually results in increasing the concentrations of salts.
Some desert fishes seem to have remarkable resistance to thermal shock.
Eremichthys acros has been subjected experimentally to reciprocal transfers between waters of 2° and 23°C (Nyquist, 1963) without apparent
adverse reaction. Cyprinodon n. nevadensis withstood changes from 2.8°
to 23.9°C in December, 9.2° to 38.4°C in March, and 26° to 43.5°C
in September over a 9- to 15-hour period under experimentally confined conditions in the field. Cyprinodon baconi from the Bahamas, where
water temperatures may vary from 10° to 37°C (Krumholz, 1963), but
rarely do so, is capable of withstanding cold shock down to 6°C. It
quickly revives, if not held at that low level (Fries, 1952). By contrast,
acute temperature changes (of about 15°C) are lethal to both golden
shiners (Notemigonus
crysoleucus)
and Virgin River spinedace
(Lepidomeda mollispinis) (Espinosa and Espinosa, 1970), and changes
of about 15°C or more kill salmonids (Black, 1953; Brett, 1941). Desert
fishes often move abruptly from shallow, hot waters, to cold, deeper
waters, or vice versa, when startled or to feed, and this may involve
changes of 10°C or more in a deep, stratified pool.
Restriction of a species to relatively narrow thermal ranges may be imposed at some level of development other than the adult. This has been
suggested for some marine species whose eggs have precise temperature
requirements (Norris, 1963). Kinne and Kinne (1962a) demonstrated developmental arrest of embryos of desert pupfish at a constant temperature
of 36°C. Different developmental stages also had different thermal optima.
An actual need for variation may also exist in development of gametes
or for completion of various other stages in diverse life cycles. This has
been discussed in reference to aquatic invertebrates in springs (Ide, 1935),
and almost certainly applies as well to fishes.
B. CHEMICAL CONDITIONS
1. Hydrogen-Ion Concentration
Hydrogen-ion concentration, expressed as pH, is of little consequence
to fishes except at its upper and lower ranges ( > 9 . 5 or<4.0; Jones,
JAMES E. DEACON AND W. L MINCKLEY
application of stress. The relatively brief exposure to thermal stress at midday doubtless results in similar phenomena that are rectified at times of
more hospitable conditions.
Probably significantly related to the above mechanism is the observation
by Schlieper et al. (1952) that brown trout and Planaria alpina survive
longer at lethal temperatures and show a reduction in the rate of increase
of respiration as temperature increases when much Ca
2+
is added to the
medium. As temperatures of desert pools increase in the summer, evaporation usually results in increasing the concentrations of salts.
Some desert fishes seem to have remarkable resistance to thermal shock.
Eremichthys acros has been subjected experimentally to reciprocal transfers between waters of 2° and 23°C (Nyquist, 1963) without apparent
adverse reaction. Cyprinodon n. nevadensis withstood changes from 2.8°
to 23.9°C in December, 9.2° to 38.4°C in March, and 26° to 43.5°C
in September over a 9- to 15-hour period under experimentally confined conditions in the field. Cyprinodon baconi from the Bahamas, where
water temperatures may vary from 10° to 37°C (Krumholz, 1963), but
rarely do so, is capable of withstanding cold shock down to 6°C. It
quickly revives, if not held at that low level (Fries, 1952). By contrast,
acute temperature changes (of about 15°C) are lethal to both golden
shiners (Notemigonus
crysoleucus)
and Virgin River spinedace
(Lepidomeda mollispinis) (Espinosa and Espinosa, 1970), and changes
of about 15°C or more kill salmonids (Black, 1953; Brett, 1941). Desert
fishes often move abruptly from shallow, hot waters, to cold, deeper
waters, or vice versa, when startled or to feed, and this may involve
changes of 10°C or more in a deep, stratified pool.
Restriction of a species to relatively narrow thermal ranges may be imposed at some level of development other than the adult. This has been
suggested for some marine species whose eggs have precise temperature
requirements (Norris, 1963). Kinne and Kinne (1962a) demonstrated developmental arrest of embryos of desert pupfish at a constant temperature
of 36°C. Different developmental stages also had different thermal optima.
An actual need for variation may also exist in development of gametes
or for completion of various other stages in diverse life cycles. This has
been discussed in reference to aquatic invertebrates in springs (Ide, 1935),
and almost certainly applies as well to fishes.
B. CHEMICAL CONDITIONS
1. Hydrogen-Ion Concentration
Hydrogen-ion concentration, expressed as pH, is of little consequence
to fishes except at its upper and lower ranges ( > 9 . 5 or<4.0; Jones,