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<br />YlL DESERT FISHES
<br />
<br />427
<br />
<br />cellular bones (Anguilla anguilla, lctalurus melas). This effect was not
<br />demonstrated in Fundulus heteroclitus, a species with acellular bone.
<br />These mechanisms are called into play immediately when there is a
<br />change in the osmotic composition of the environment. In Fundulus kansae
<br />complete adaptation to seawater after direct transfer from fresh water oc-
<br />curs in 20 days. Hypertonic environments become lethal to fishes when
<br />the capacity of the secretory cells of the gills (and oral epithelium) and
<br />kidney is exceeded and salt begins to accumulate in the tissues.
<br />Salinity tolerances of different stages in a life cycle may vary radically.
<br />Kinne (1960) and Kinne and Kinne (1962a,b) demonstrated that eggs of
<br />Cyprinodon macularius will develop in salinities up to 70 gm/liter (with
<br />varying rates and structural consequences), whereas adults live in salinities
<br />up to 80 to 8S gm/liter. Barlow (1958b) indicates that juveniles of C.
<br />macularius are capable of surviving in salinities up to 90 gm/liter, but that
<br />most adults die sooner. Renfro (1960) reported survival of yolk-sac larvae
<br />of sheepshead pupfish at 110 gm/liter. Our observations of other species
<br />of pupfishes in drying pools indicate a greater tolerance of subadults than
<br />of either tiny young, or larger old individuals.
<br />Minimum salinity tolerances have been infrequently reported, LaBounty
<br />and Deacon (1971) maintained adult Cyprinodon salinus and Cyprinodon
<br />sp, from Death Valley in distilled water. Kinne and Kinne (1962a) found
<br />that some eggs of C. macularius developed in glass-distilled water, although
<br />mortality was quite high. They documented normal development over a
<br />wide range of temperature in water made up of half tap water and half
<br />distilled water. Simpson and Gunter (1956) caught C. variegatus at
<br />1.8 gm/liter, and Gunter (1950) recorded it at 0.4 gm/liter. Kilby (1955)
<br />recorded a minimum for that species of 0.0 gm/liter, a highly unlikely
<br />total dissolved solids determination from natural water. The Australian
<br />Taeniomembras studied by Lee (1969) lived for a week after direct trans-
<br />fer from 70 gm/liter to 2.0 gm/liter salinity, but mortality was about 50%.
<br />Such changes in nature, in an almost instantaneous manner, certainly occur
<br />when marginal pools are rapidly flooded by rising streams or lakes, or dur-
<br />ing heavy, seasonal rainfall, or when waves suddenly fill shore pools along
<br />margins of desert lakes.
<br />
<br />3, Dissolved Gases
<br />
<br />Dissolved gases have been far less studied relative to desert fishes
<br />than have physical and more easily analyzed chemical featurcs. Incidental
<br />analyses have bccn gcnerally omitted here, unless directly pcrtaining to
<br />a species or group of fishes; references to broad limnological works dealing
<br />in part with dissolved gases are given earlier. Flowing waters, other than
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