432
JAMES E. DEACON AND W. L. MINCKLEY
than 100 mm Hg in more resistant forms (ictalurids, cyprinids, and others;
Fry, 1957). No typical desert species have been studied, but changes in
pH, dissolved oxygen, temperature, and so on, in desert habitats, indicate
comparable changes in other gases and ions and vast tolerances to carbon
dioxide in some species.
Schaut (1939) observed no adverse reaction by unspecified minnow species exposed to carbon dioxide-free water for 2 hours.
c. Hydrogen Sulfide. Hydrogen sulfide is commonly present within the
bottoms of desert aquatic habitats, but few actual measurements of its concentration are available. The most extreme example we have found is by
Smith (1952) in a small, sulphur-depositing marsh in Cyrenaica which
contained a range of 12-200 mg/liter. Cyprinodon ( = Aphanius) dispar
and C. ( = A.) jasciatus were living in that habitat, being taken only in
the areas of lower concentration (but no search was made for them elsewhere); other features of this extreme habitat are given in Table II. Kosswig (1961) illustrated cyprinodontids in some waters of the Anatolian
basin, Turkey, with their bodies covered by (elemental?) sulfur, and
noted production of sulfur compounds in shallow waters, presumably as
a result of oxidation of hydrogen sulfide.
Jones (1964) indicates a decreasing toxicity of hydrogen sulfide to fishes
with increases in pH. This occurs because un-ionized hydrogen sulfide penetrates living tissue more readily than its disassociated ions do, as also
is true of cyanide, and the proportion of undisassociated gas increases with
decreases in pH. This has been demonstrated for numerous teleosts of a
number of families (Jones, 1964; Bonn and Follis, 1967). The toxicity
of hydrogen sulfide seems based on the sulfide, which creates a tissue
anoxia resulting from inactivation of respiratory carriers. If concentrations
are not too great, sulfide may be oxidized within the body to relatively
innocuous sulfate; thus recovery from sublethal dosage may be expected.
General levels of tolerance for hydrogen sulfide range from about
1 mg/liter for trout, to 8-12 mg/liter for carp (Cyprinus carpio) and
tench {Tinea tinea). Schaut (1939) found unspecified minnows to be
killed after a short exposure to water containing 6 mg/liter hydrogen sulfide, but to survive with no apparent adverse reaction during 24 hours of
exposure to 4 mg/liter. An initial concentration of 5 mg/liter hydrogen
sulfide was reduced to 1.4 mg/liter during a 24-hour period. This test condition produced a 50% fish mortality.
Mechanisms utilized by Aphanius in surviving > 12 mg/liter hydrogen
sulfide are unknown and were not investigated by Smith (1952). The pH
was 7.4, which might have aided in reducing the unionized component
of the concentration. In shallower, desert waters the presence of hydrogen
sulfide in daytime may be essentially prevented by oxidizing effectiveness
JAMES E. DEACON AND W. L. MINCKLEY
than 100 mm Hg in more resistant forms (ictalurids, cyprinids, and others;
Fry, 1957). No typical desert species have been studied, but changes in
pH, dissolved oxygen, temperature, and so on, in desert habitats, indicate
comparable changes in other gases and ions and vast tolerances to carbon
dioxide in some species.
Schaut (1939) observed no adverse reaction by unspecified minnow species exposed to carbon dioxide-free water for 2 hours.
c. Hydrogen Sulfide. Hydrogen sulfide is commonly present within the
bottoms of desert aquatic habitats, but few actual measurements of its concentration are available. The most extreme example we have found is by
Smith (1952) in a small, sulphur-depositing marsh in Cyrenaica which
contained a range of 12-200 mg/liter. Cyprinodon ( = Aphanius) dispar
and C. ( = A.) jasciatus were living in that habitat, being taken only in
the areas of lower concentration (but no search was made for them elsewhere); other features of this extreme habitat are given in Table II. Kosswig (1961) illustrated cyprinodontids in some waters of the Anatolian
basin, Turkey, with their bodies covered by (elemental?) sulfur, and
noted production of sulfur compounds in shallow waters, presumably as
a result of oxidation of hydrogen sulfide.
Jones (1964) indicates a decreasing toxicity of hydrogen sulfide to fishes
with increases in pH. This occurs because un-ionized hydrogen sulfide penetrates living tissue more readily than its disassociated ions do, as also
is true of cyanide, and the proportion of undisassociated gas increases with
decreases in pH. This has been demonstrated for numerous teleosts of a
number of families (Jones, 1964; Bonn and Follis, 1967). The toxicity
of hydrogen sulfide seems based on the sulfide, which creates a tissue
anoxia resulting from inactivation of respiratory carriers. If concentrations
are not too great, sulfide may be oxidized within the body to relatively
innocuous sulfate; thus recovery from sublethal dosage may be expected.
General levels of tolerance for hydrogen sulfide range from about
1 mg/liter for trout, to 8-12 mg/liter for carp (Cyprinus carpio) and
tench {Tinea tinea). Schaut (1939) found unspecified minnows to be
killed after a short exposure to water containing 6 mg/liter hydrogen sulfide, but to survive with no apparent adverse reaction during 24 hours of
exposure to 4 mg/liter. An initial concentration of 5 mg/liter hydrogen
sulfide was reduced to 1.4 mg/liter during a 24-hour period. This test condition produced a 50% fish mortality.
Mechanisms utilized by Aphanius in surviving > 12 mg/liter hydrogen
sulfide are unknown and were not investigated by Smith (1952). The pH
was 7.4, which might have aided in reducing the unionized component
of the concentration. In shallower, desert waters the presence of hydrogen
sulfide in daytime may be essentially prevented by oxidizing effectiveness