Reprinted from COPEIA, 1955, No. 2, pp. 104-106, May 20
Printed in U.S.A.
Fish Respiration in the Natural Oxygen Gradient of an
Anaerobic Spring in Florida
HOWARD T. ODUM AND DAVID K. CALDWELL
ON rare occasions one finds in nature an
ecological circumstance so perfectly com-
posed that it constitutes.a natural experiment
superior to any man-made construction that
could be built at reasonable cost in the labora-
tory. Definite inferences can then be obtained
with a small effort. Such natural experimental
situations have additional value if they are per-
manent enough for data to be cumulative. In
this communication some observations made in
one of the remarkable Florida springs are used
to draw conclusions about the respiration of
fishes. It is hoped that others will be attracted
to these permanent chemostatic gradients.
Beecher Springs, adjacent to the University
of Florida Conservation Reserve, Welaka, Put-
nam County, emerges from a limestone aquifer
without oxygen. As it flows downstream in its
run (Fig. 1) this small stream picks up oxygen
by diffusion and by photosynthesis of the algae.
At a constant temperature diurnally and sea-
sonally of 22 to 230C., the physical and biologi-
cal characteristics of this spring seem constant
as surveyed 6 times over a period of 3 years.
Extensive work on trace elements in another
spring, Silver Springs, Marion County, indi-
cates that a chemostatic condition is to be
expected in the springs of the region. Thus
Beecher Springs seems to constitute a perma-
nent oxygen gradient in which organisms have
become adjusted. White sulfur bacteria and
blue-green algae dominate the boil with other
algal types appearing downstream, and finally
higher plants appear 300 meters from the boil.
The algae have been studied by Larry A. Whit-
ford, North Carolina State College, and will be
the subject of a forthcoming paper by him.
Midges (Tendipedidae and Heleidae) are found
throughout the run and in part are the basis of
the food chain leading to some of the fishes.
The oxygen values on the map (Fig. 1) were
obtained with the Rideal-Stewart-Winkler
method. Essentially similar values were re-
corded on June 6, 1952 and a year later on June
22, 1953. There are clearly eddies of water in
the stream so that oxygen conditions at any one
point fluctuate slightly with a range of about
1 ppm. Some idea of this variation from eddy
to eddy can be obtained from the data in
Table I. The analytical accuracy is about 0.1
ppm plus or minus.
The water is cear and the boil area smells
strongly of sulfurous gases. Other properties
are as follows: carbon dioxide, 10 ppm; pH,
7.2-7.7; chlorides, 166 ppm; phosphorus, 0.14
ppm; nitrate nitrogen, 0.02 ppm; alkalinity,
105 ppm (CaCOa); hydrogen sulfide, 0.02 ppm.
The natural distribution of fishes in this
natural gradient was observed with the aid of
a face mask by swimming underwater where
clear visibility is 30 meters or more. The ob-
served species distribution is indicated in Fig. 1
and is listed below. The eddies of water permit
local temporary microhabitats to acquire more
oxygen so that fishes can move into the higher
oxygen spots to replenish oxygen and thus can
live in parts of the stream where the average
oxygen may be below their physiological toler-
ances. Fig. 1 shows ecological tolerances under
stream conditions by indicating the farthest
H. T. ODUM AND D. K. CALDWELL-ANAEROBIC SPRING
Fig. 1. Map of Beecher Springs, Welaka, Florida. Dissolved oxygen values are given in parts per million.
The nearest that the fish were observed to come to the boil is indicated for 12 species in the middle of a
sunny day (June 24, 1953).
point upstream that each species was observed
to go. It is possible that the decrease of the small
hydrogen sulfide concentration downstream is
also involved. In order of distribution down
the spring run the fishes represented are: eastern
gambusia, Gambusia affinis holbrooki (Girard);
sailfin molly, Mollienesia latipinna LeSueur;
Least killifish, Heterandriaformosa Agassiz; red-
fin killifish, Lucania goodei Jordan; shellcracker,
Lepomis microlophus (Gunther); redfin pickerel,
Esox americanus Gmelin; redbreast sunfish,
Lepomis auritus (Linnaeus); largemouth bass,
Micropterus salmoides (Lac6pede); chubsucker,
Erimyon succetta (Lac6pede); bluegill, Lepomis
macrochirus Rafinesque; golden shiner, Notemi-
gonus crysoleucas (Mitchill); and bowfin, Amia
EXPERIMENTS IN SUBMERGED CAGES
Although Habs and Mueller (1948) found
that the eastern gambusia lived readily in 0.3
ppm oxygen, the abundance of three cyprino-
dont species in the churning outflow headwaters
(boil) where the oxygen is less than 0.3 ppm
day and night seemed remarkable. These fishes
are observed to break the surface continually.
-vollys feeding on the bottom swim to the sur-
face frequently before returning to the bottom.
Although gulping by these fishes has long been
observed, the writers do not know of a cear
demonstration of the.thresholds at which gulp-
ing is necessary for these widespread fishes.
The following experiments were conducted
within the springs.
DISSOLVED OXYGEN, IN PARTS PER MILLION, IN
BEECHER SPRINGS, FLORIDA
For 1953, three analyses for each station are preceded by the
mean of these values. For stations, see Fig. I
Station VI:6:1952 VI:24:1953
Boil A 0.05 0.3 (0.27, 0.30, 0.50)
B 0.26 0.6 (0.50, 0.59, 0.65)
C 0.9 1.1 (0.40, 0.65, 2.16)
BoilD 1.3 0.2 (0.21, 0.13, 0.29)
E 1.7 1.3(1.26, 1.31, 0.99)
F 1.1 2.0 (2.30, 1.80, 2.01)
G ... 2.3 (3.51, 1.15, 2.32)
Gambusia and Mollienesia taken from the
boil were placed in the following situations:
1. Out of water in a dry box on land.
2. In cages in the boil at the surface so that
fish could gulp at the surface.
3. In 4 cages submerged in the boil so that
fishes could not get closer than 1 inch to
the surface. One cage was near the surface
and one was at a depth of 2 feet. A third
cage included only Gambusia and a fourth
4. Submerged below the surface downstream
where the oxygen was 1.3 ppm. (See Fig. 1.)
The amounts of time required for the fishes
to die are summarized in Table II. Where
oxygen was inadequate, distress was noticed
within three minutes and most of the fishes
were dead in about half the time necessary for
all to succumb. Although Gambusia and
MoUienesia are readily observed to pump the
surface film over their gills in stagnant waters
COPEIA, 1955, NO. 2
FISH SURVIVAL EXPERIMENTS IN BEECHER SPRINGS,
JANUARY 11, 1953
Experimental situation Nu tbe
Cage in the boil at the surface
of the water, fish gulping
Completely out of water*..... 30
Cages completely submerged
Gambusia, avg. weight: .23
gm ................... 27
Mollieesia, avg. weight:
0.37 gms............. 27
Gambusia and Mollienesia:
Below the surface 1 inch.. 24
Below the surface 2 feet... 48
Cage completely submerged
* Gambsia and Mollienesia.
where oxygen is low, this is not the means of
respiration in this turbulent but anaerobic
stream. Definite gulping of air is observed. That
gulping is necessary at these low tensions is
demonstrated by the survival of those fishes
with access to the surface. Since there was a
rapid turbulent current cascading upward
through the experimental cages an oxygenated
surface film could not develop. When pre-
vented from gulping, the fish drowned quickly.
Those fishes kept out of water were quite alive
at the end of 22 minutes since they demon-
strated normal behavior when returned to the
Whereas the respiration of air by fishes has
been much studied, the mechanism of aerial
respiration in small cyprinodont fishes seems to
have been neglected. Our dissections indicate
that the Beecher Springs individuals do not
differ from Gambusia affinis holbrooki elsewhere
in having a closed swim bladder, a short intes.
tine opening directly into a short oesophagus,
and pseudobranchs (Vialli, 1926). These latter
vascularized structures lining the pharynx may
be the structures used as a respiratory surface
for gulped air.
Another anaerobic spring in which obligate
gulping by fish may be directly inferred is the
large Warm Salt Spring in Sarasota County,
Florida. Here, tarpon, Tarpon atlanticus (Valen-
ciennes); gar, Lepisosteus sp.; southern varie-
gated cyprinodon, Cyprinodon variegatus varie-
gatus (Lac6pede); sailfin mollys, and eastern
gambusia are found in about half sea water
salinity (17,800 ppm) and a temperature of
31C. The oxygen content is between 0.00 and
0.81 ppm day and night. The tarpon were ob-
served to roll and the smaller fishes to break
the water continually. That tarpon and gars
breathe with a vascularized air bladder is
known from observations and dissections sum-
marized by Babcock (1951) for the tarpon and
Jones and Marshall (1953) for the gar.
These studies were aided by a contract be-
tween the Office of Naval Research, Depart-
ment of the Navy, and the University of Flor-
ida, NR 163-106.
BABCOCK, Louis L. 1951. The Tarpon. 5th ed.
Privately published, 157 pp., illus.
HABS, H., AND G. MUELLER. 1948. Uber das
Verhalten der Gambusien gegenuber dem Sauer-
stoffgehalt des Wassers. Zeitschr. Hgy. u. Infek-
tienskrankh. 128: 371-8. (Abstract)
JONES, F. R., AND N. B. MARSHALL. 1953. The
structure and function of the teleostean swim
bladder. Biol. Rev. 28: 16-83.
VIALLI, M. 1926. Le pseudobranchie dei Pesci
Arch. Ital. Anat. Embriol., 23: 49-117 (Abstract)
DEPARTMENT OF BIOLOGY, UNIVERSITY OF
FLORIDA, GAINESVILLE, FLORIDA.