V I I . DESERT FISHES
421
1964). Most desert waters we have studied are slightly to strongly alkaline
and have pH values between 7.2 and 9.0, or so. Values above 8.6 are
associated with high salinities or with high photosynthetic rates of plants
that are capable of utilizing half-bound carbon dioxide. Spring waters are
typically circumneutral, buffered by interactions of free carbon dioxide and
various ions (principally bicarbonates), but they may sometimes be somewhat acidic. Downflow changes in such waters, principally the loss of free
carbon dioxide from the water surface and through photosynthetic activities, may result in deposition of carbonates (travertines) in the channels,
and this may be quickly detected by pH determination (Cole and
Batchelder, 1969). Ranges of pH at which desert fishes have been found
are given in Table II.
2. Salinity
Desert fish habitats are not only characterized by impressive thermal
extremes, but equally by their high content of dissolved solids. This of
course is a natural consequence of surface water standing in a desiccating
environment. Flushing action which maintains the fresh character of waters
in exorheic zones is an infrequent occurrence in endorheic situations.
The hypersaline commonality of desert waters was stressed by Cole (1968),
who also noted the numerous, relatively unique exceptions. In light of
these facts, it is not surprising that some of the most striking adaptations
to hypersaline conditions are among desert fishes and their relatives. Unfortunately, opportunities for elucidation of such adaptations have yet to
be exploited in any major way. Much of our discussion of the life of desert
fishes in hypersaline conditions is speculative, fragmentary, and largely dependent upon data from fishes living in less extreme environments.
Terminology to be used in reference to waters of high dissolved solid
content may become complex (Hedgpeth, 1959; Macan, 1963; Bayly,
1967). We use the term salinity in the sense of Hutchinson (1957) "as
the concentration of all ionic constituents present." But we are in complete
sympathy with the need for more precise designation of chemical features
of aquatic habitats and thus provide in Table II a resume of chemical features of some of the more extreme desert waters in which fishes have been
found. Differences in the ways of reporting salinities in the literature, ranging from specific gravities to diverse gravimetric units per volume, also
complicate the issue, and some comparisons may be rather crude. We
present the approximate relationships of various types of measurements
in Fig. 5.
As with temperature, chemical stratification and other microdifferences
may confuse field measurements of salinities, and a few percentage points
may be exceedingly important to fishes distributing themselves relative to
421
1964). Most desert waters we have studied are slightly to strongly alkaline
and have pH values between 7.2 and 9.0, or so. Values above 8.6 are
associated with high salinities or with high photosynthetic rates of plants
that are capable of utilizing half-bound carbon dioxide. Spring waters are
typically circumneutral, buffered by interactions of free carbon dioxide and
various ions (principally bicarbonates), but they may sometimes be somewhat acidic. Downflow changes in such waters, principally the loss of free
carbon dioxide from the water surface and through photosynthetic activities, may result in deposition of carbonates (travertines) in the channels,
and this may be quickly detected by pH determination (Cole and
Batchelder, 1969). Ranges of pH at which desert fishes have been found
are given in Table II.
2. Salinity
Desert fish habitats are not only characterized by impressive thermal
extremes, but equally by their high content of dissolved solids. This of
course is a natural consequence of surface water standing in a desiccating
environment. Flushing action which maintains the fresh character of waters
in exorheic zones is an infrequent occurrence in endorheic situations.
The hypersaline commonality of desert waters was stressed by Cole (1968),
who also noted the numerous, relatively unique exceptions. In light of
these facts, it is not surprising that some of the most striking adaptations
to hypersaline conditions are among desert fishes and their relatives. Unfortunately, opportunities for elucidation of such adaptations have yet to
be exploited in any major way. Much of our discussion of the life of desert
fishes in hypersaline conditions is speculative, fragmentary, and largely dependent upon data from fishes living in less extreme environments.
Terminology to be used in reference to waters of high dissolved solid
content may become complex (Hedgpeth, 1959; Macan, 1963; Bayly,
1967). We use the term salinity in the sense of Hutchinson (1957) "as
the concentration of all ionic constituents present." But we are in complete
sympathy with the need for more precise designation of chemical features
of aquatic habitats and thus provide in Table II a resume of chemical features of some of the more extreme desert waters in which fishes have been
found. Differences in the ways of reporting salinities in the literature, ranging from specific gravities to diverse gravimetric units per volume, also
complicate the issue, and some comparisons may be rather crude. We
present the approximate relationships of various types of measurements
in Fig. 5.
As with temperature, chemical stratification and other microdifferences
may confuse field measurements of salinities, and a few percentage points
may be exceedingly important to fishes distributing themselves relative to