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<br />316
<br />
<br />JAMES E. DEACON AND W. L MINCKLEY
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<br />, 7
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<br />have disappeared as new ones arose. Some fish species have been dis-
<br />persed widely, by accident or design. Other, native ones, have been
<br />extirpated, or their stocks were greatly depleted forcing them back into the
<br />most inaccessible parts of their ranges. In this chapter we stress, insofar as
<br />possible, the inland, indigenous fishes of deserts; their habitats in the
<br />pristine state; and their behavioral, morphological, and physiological
<br />adaptations for life.
<br />Fishes as a g'roup are remarkably diversified, reflecting in considerable
<br />detail the rigorous environmental forces under which they operate. Special
<br />environmental features require special adaptations, "adjustments. . . to di-
<br />verse niches in the environment" (Hubbs, 1941a). Thus, some perpetu-
<br />ally torrential streams support highly specialized fishes and other animals
<br />that have evolved sucking discs or hooks. Modifications of their mouths,
<br />fins, or other body parts hold against the constant turbulence and thrust of
<br />current (Hora, 1922). At the other extreme, downstream parts of rivers,
<br />lakes, or quiet springs are lentic in nature, and deep-bodied, slowly moving
<br />fishes may predominate. In open water of quieter places, small, slim,
<br />silvery species occupy pelagic space. Some moderately heavy-bodied forms
<br />live on or near the bottoms. In rocky areas or dense beds of aquatic
<br />vegetation, laterally compressed, deep-bodied, or elongated, snake-like
<br />forms may occur (Nikolsky, 1961, 1963; Lagler et aI., 1962).
<br />In habitats between extremes, creeks of intermediate gradient, for exam-
<br />ple, a major proportion of the fishes are typically small, with rounded
<br />bodies and moderately expansive fins. A limbo of variability in such en-
<br />vironments, from torrent in flood to pool in drought, dictates a highly
<br />adaptable body form and function. With a few notable exceptions, fishes
<br />successful in desert waters display generalized shapes. A few minor adjust-
<br />ments in form and function allow their successful exploitation of the some-
<br />times harsh environments.
<br />Coverage in this chapter emphasizes hotter deserts of southwestern
<br />United States and northern Mexico, which are the geographic focus of our
<br />researches. Information on fishes and aquatic habitats of those regions
<br />not spccifically attributcd to other sources is compiled from our unpub-
<br />lished data. We follow Cole (1968) in embracing a broader definition of
<br />desert than might a terrestrial ecologist, since many waters discussed here
<br />transcend a number of biomes. With the exception of springs fed by
<br />subterranean waters, aquatic habitats of arid lands depend upon surface
<br />flow or subsurface infiltration 01' water from adjacent, more mesic zones
<br />(Smith, 1968). Spccial adaptations of fishcs to aquatic circumstances in
<br />nondesert regions, which parallel those of desert species, are also drawn
<br />upon. However, discussion of fish spedes alien to deserts, but now present
<br />there, is limited generally to effects they have had upon systems into
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