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Growth of the turtle Chrysemys scripta under constant controlled laboratory conditions.

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THE ANATOMICAL RECORD 199433-439 (1981)
Growth of the Turtle Chrysernys scripta
Under Constant Control led Lab0 ratory Conditions
BERNARD G. SARNAT, ELIZABETH MCNABB, AND MICHAEL GLASS
Section of Oral Biology, School of Dentistry; Division of Plastic Surgery,
Department of Surgery, School of Medicine; and Dental Research Institute;
Uniuersity of California at Los Angeles, L o s Angeles, California 90024
ABSTRACT
The purpose of this study was to determine 1) growth of the turtle
shell and change in weight under constant controlled laboratory conditions and
2) whether under these constant conditions there were seasonal changes. Fifty
unfed refrigerated eight-week-old hatchling turtles Chrysemys scripta were received in October and maintained in aquaria with 16 hours of artificial light and
eight hours of darkness, at 24-27°C and a humidity of 30% and fed twice weekly.
Gross linear measurements of the width and length of the plastron and carapace,
and total body weights, were taken a t eight weeks and thereafter a t about six-week
intervals. During the two-year period the mean increase of the plastron length was
from 30.79 t 0.19 mm to 68.32 t 1.58 mm, plastron width from 24.23 t 0.20 mm
to 50.43 % 1.03 mm; carapace length from 32.47 t 0.24 mm t o 75.21 t 1.82 mm,
carapace width from 31.81 t 0.28 mm to 67.12 1.29 mm, and body weight from
6.94 0.15 gm to 80.63 % 5.02 gm.Calculated daily percent changes revealed that
as the turtles aged, the rates decreased. At 56 days of age, weight was the most
strongly correlated with its value at 786 days of age. No seasonal differences in
growth were noted between the summer and winter periods when turtles would
enter winter dormancy in certain natural environments. Environmental factors
are reflected in the growth of the turtle
*
Although there are many references about
growth of turtles in varied natural environments, there are few references about
growth of the turtle in captivity or under constant controlled conditions in the laboratory
(Cagle, '46, '50; Allen and Littleford, '55;
Jackson, '70; Ernst and Barbour, '72; Wilbur,
'75; Christiansen and Burken, '79). The purposes of this study were to determine under
constant controlled laboratory conditions during a two-year period beginning a t the hatchling stage the growth rate of Chrysemys scripta
by measuring weight, width, and length of the
shell (plastron and carapace); whether under
these constant conditions there were seasonal
changes as in certain natural environments;
and which measurements were most reliable as
growth indicators. No similar report was noted
in the literature.
MATERIALS AND METHODS
Fifty unfed refrigerated eight-week-old
hatchling red-eared turtles Chrysemys scripta
were received from a commercial turtle dealer
in October. Within the first week each turtle
0003-276X/81/19930433$02.50 0 1981 ALAN R. LISS, INC.
*
was topically numbered on selected scutes of
the carapace with an indelible felt-tip black
marker. They were housed according to size
and in groups of four to five, in 11 glass aquaria
(40-80 liters each). The turtles were exposed to
16 hours of artificial light and eight hours of
darkness for each 24-hour period. Ambient laboratory temperature was 2 6 2 7 ° C with a humidity factor of 300/00.The water was aerated,
filtered, and had 0.005% sodium hypochlorite
added each week to inhibit bacterial and algal
growth. Also included in the aquaria were
floating platforms to enable the turtles to get
out of the water.
The turtles were maintained on a mixed fortified diet of fish, bone meal and multiple vitamins. They were fed ad libitum twice weekly;
once on Monday (when the aquaria were
cleaned) and again on Thursday. One medium-sized leaf of romaine lettuce was
added to each aquarium a t the conclusion of
feeding sessions as a food supplement, and
mealworms (3-4 per turtle) were given on an
Received May 7, 1979 accepted July 11, 1980.
BERNARD G. SARNAT, ELIZABETH MCNABB, AND MICHAEL GLASS
434
95% confidence interval and the mean at each
time period is given in Figures g 7 for weight,
carapace length and width, and plastron length
and width. The general trend in all five figures
is for the daily percent change to decrease as
the animals aged. The very high daily percent
change in weight for the first interval (5G70
days) might possibly represent hydration of the
turtles (Fig. 3). The two measures of carapace
(Figs. 4, 5 ) and pastron length (Fig. 6) might
indicate a spurt during the first summer but
not in the second.
The correlation between weight values a t 56
and 786 days of age is highly significant (r =
0.540, P < 0.001, N = 37), whereas that between carapace width values at 56 and 786 days
of age is not statistically significant (r = 0.293,
P > 0.05). At 148 days, however, the correlation with 786 days of age is highly significant
(r = 0.513, P < 0.001).The correlationbetween
carapace length values at 56 and 786 days of
age is significant (r = 0.394, P < 0.05) and becomes highly significant a t 70 and 786 days of
age (r = 0.528, P < 0.001).This same pattern is
RESULTS
observed for plastron width values with the
The approximate relative size of the carapace corresponding correlation coefficients equal to
and plastron on a centimeter grid and dorso- 0.316 and 0.510. The correlation between the
ventral radiographs from 58 to 810 days of age plastron lengthvalues a t 56 and 786 days of age
are illustrated in Figure 1. The superposed is significant (r = 0.386, P < 0.05) and is highly
tracings of the photographs of the plastrons a t significant a t 148 days of age (r = 0.516, P <
58,443, and 810 days of age illustrate (Fig. 2) 0.001). Each measurement at an early age is
the differential in growth.
significantly related to its value a t 786 days of
The growth patterns of weight, carapace age. These correlations show weight to be correlength and width, and plastron length and lated most strongly at 56 days of age and that
width were calculated for each turtle as an av- the carapace and plastron measurements are
erage daily percent change. An approximate strongest at 70 and 148 days of age.
infrequent, treat basis. For each aquarium
there was a separate 8-10-liter stainless steel
container used for a g4-hour feeding period.
Data were collected and recorded first a t
eight weeks of age and thereafter at about sixweek intervals for the first 18 months, and a t
about 12-weekintervals for the last six months.
Gross direct linear measurements of the maximum width and length of the carapace and
plastron were recorded to the nearest 0.1 mm
with a sliding Helios dial reading needlepointed caliper. Each measurement was taken
twice. An average of the two values was used.
Weights were recorded to the nearest 0.1 gm
with the use of a two-pan triple beam balance.
Radiographs were obtained a t the beginning
usually at a targetlfilm distance of 50 cm, with
the X-ray machine operated a t 40 kVp, 15 mA,
and a n exposure time of 4 seconds and after
about 4 months when the turtles were larger
and more mineralized at a targetlfilm distance
of 70 cm, 65 kVp, 10 mA, and a n exposure time
of 2 seconds.
TABLE 1. Mean weights, and carapace and plastron widths and lengths and their associated standard errors
of turtles at 16 intervals from 56 to 786 days of age
Carapace
Plastron
Dates
Age in
days
Weight (gm)
Width (mm)
Length (mm)
Width (mm)
Length (mm)
1015
10119
11/18
115
2116
3/31
5/11
6122
814
9/15
10127
1215
1/19
417
715
1014
56
70
100
148
190
233
274
316
359
40 1
443
482
527
606
695
786
6.94 t 0.15
9.18 t 0.14
10.31 t 0.20
15.59 t 0.50
20.88 t 0.77
27.16 f 1.02
32.01 f 1.31
36.77 t 1.63
41.63 % 1.80
46.10 t 2.35
50.27 t 2.76
54.70 t 2.96
59.05 t 3.35
63.52 c 3.72
73.72 2 4.39
80.63 t 5.02
31.81 t 0.28
31.71 t 0.26
33.06 t 0.29
37.78 ? 0.42
41.80 f 0.54
46.11 t 0.61
49.07 t 0.65
51.91 t 0.74
55.01 t 0.81
56.83 f 0.93
58.23 t 1.01
59.35 t 1.05
60.92 t 1.09
62.82 t 1.18
64.75 t 1.29
67.12 t 1.29
32.47 f 0.24
33.23 +- 0.24
35.16 x 0.29
40.86 % 0.48
44.97 2 0.72
49.86 t 0.71
53.02 t 0.81
55.81 t 0.93
59.16 t 0.97
61.27 2 1.18
62.88 ? 1.32
64.57 ? 1.35
66.69 t 1.43
69.34 c 1.59
72.47 t 1.69
75.21 ? 1.82
24.23 f 0.20
24.23 t 0.19
25.40 t 0.21
29.96 t 0.34
33.29 t 0.44
36.17 t 0.48
38.19 t 0.51
40.21 f 0.70
42.15 t 0.62
43.35 t 0.74
44.25 2 0.78
45.11 0.83
46.72 f 0.90
47.61 f 0.92
49.61 f 1.00
50.43 t 1.03
30.79 t 0.19
30.89 2 0.23
32.22 c 0.24
36.96 c 0.39
41.08 f 0.52
44.79 t 0.59
47.79 t 0.67
50.17 t 0.81
53.69 f 0.94
55.50 t 1.09
56.98 t 1.18
58.33 t 1.17
60.56 e 1.23
63.03 t 1.39
66.37 t 1.47
68.32 t 1.58
*
TURTLE GROWTH IN LABORATORY
435
Fig. 1. Photographs of approximate relative size of carapace and plastron on a centimeter grid and dorsoventral radiographs from 58 to 810 days of age. Note change in ocelli on the plastrons (Table 1).
BERNARD G. SARNAT, ELIZABETH MCNABB, AND MICHAEL GLASS
436
4
Fig. 2. Superposedtracings of plastron photographs of a turtle. Note the differentialin growth between 58 and
443 days, and 443 and 810 days of age (see Fig. 1 and Table 1).
WEIGHT
-
Mean
..__.
'2 Standard Errors
2
:
8 1.0
I
\
DBC1
Apr 1
Aug
1
Dec 1
Apr I
Age in Days
Figs. %7.
Daily percent change is defined from the mid-point of each age interval during the two-year period.
Fig. 3. Weight.
437
TURTLE GROWTH IN LABORATORY
CARAPACE LENGTH
-
Mean
.....f2 Standard Errors
Dec 1
Apr 1
Dec I
Aug I
A ~ 1I
Age in Days
Fig. 4. Carapace length.
CARAPACE WIDTH
-
Mean
._.
..Standard Errors
t2
I
D& 1
Apr I
Aug 1
Dee1
Age in Days
Fig. 5. Carapace width.
Apr 5
438
BERNARD G. SARNAT, ELIZABETH MCNABB, AND MICHAEL GLASS
PLASTRON LENGTH
--
Mean
_..
._
'2
Standard Errors
2;2
Dee I
1
I
1
380
Apr I
1
422
462
I
504
566
Dec I
Aug I
650
Apr I
I
739
Aug I
Age in Days
Fig. 6. Plastron length
PLASTRON WIDTH
-
Mean
__..f-2 Standard Errors
-&p3
Dec 1
Apr
I
337
Aug
380
1
422
562
504
Dec 1
Age in Days
Fig. 7. Pastron width.
56b
650
Apr I
739
Aug I
TURTLE GROWTH IN LABORATORY
DISCUSSION
In a study of the growth of animals the ideal
method is to make repeated observations a t
regular intervals on a large population of the
same individuals of known age living under the
same constant conditions. This we attempted to
do in the laboratory rather than repeat a study,
of which there are many excellent ones, in the
natural environment with its many uncontrolled variables (Cagle, '46, '50; Allen and
Littleford, '55; Jackson, '70; Ernst and Barbour,
'72).
The turtle shell because of its firmness, ready
availability, and with only the thin scutes covering the bone, was a n excellent model for accurate study of gross bone growth. The growth
peak was reached during the first year and
from then on the rate decelerated (Figs. S 7 )
(Cagle, '46, '50; Jackson, '70; Gibbons, '68).
In the natural environment when the water
temperature was below 10-15"C, turtles became less active and went into dormancy
(Cagle, '50; Sexton, '65; Felger et al., '76). In
this two-year experiment the temperature was
maintained between 24" and 27°C. The turtles
did not go into dormancy, and growth continued
throughout the year a t a regular rate. This
could be compared with another similar experiment except for either changing the lightldark
period or lowering the temperature for certain
periods. Although we tried to raise the turtles
under ideal conditions, there were limiting factors such as aquarium size and absence of a
natural growing plant and animal diet.
Contrary to the statement that turtles maintained in zoos or laboratories often refuse to
feed during the winter (Cagle, '50; Suzuki, '63),
our turtles fed well from October through April.
They did not become dormant, and they continued to grow. Jackson ('70) studied growth of
turtles inhabiting Fannin Spring in Florida
with a virtually constant temperature of 2 Z
23°C. A dramatic decrease in growth rate occurred over the winter months despite the turtles' remaining active and feeding. He mentioned that cold air temperatures and a shorter
day length might have been factors. Jackson
('70) stated that it was difficult to account for
what appeared to be almost a complete cessation of growth, and he raised the question of an
inherent growth cycle regulated perhaps by the
changing seasonal light/dark ratio.
439
Wilbur ('75) found that weight was the best
measure to predict furture growth. We found
this to be true a t 56 days of age. Cagle ('46)
reported in his study of turtles in the natural
environment that plastron length was the best
indicator of future growth and we found this to
be true at 148 days of age. Cagle ('50) found no
significant correlation between egg size and
plastron length in predicting future growth.
A later study will be to determine, by means
of radiopaque implants (in bones of the plastron) and serial radiographs, the contribution
of selected sutures to growth of the turtle shell
during a Z3-year period.
ACKNOWLEDGMENTS
This project was supported in part by Biomedical Research Support grant RR05304
from the National Institutes of Health.
We are grateful to Alan B. Forsythe, Onelio
Clark, and Peter Lestrel for the statistical
evaluation; Charles G. Wishowski for Figures
1 and 2; Irene Petravicius for Figures 3
through 7; and the School of Dentistry Word
Processing Center for assistance in the preparation of this manuscript.
LITERATURE CITED
Allen, J.F., and R.A. Littleford (1955)Observations on the
feeding habits and growth of immature diamondback terrapins. Herpetologica, I 1 :77-80.
Cagle, F.R. (1946)The growth of the slider turtle,Pseudemys
scripta elegans. Am. Mid. Nat., 36.685729.
Cagle, F.R. (1950) The life history of the slider turtle
Pseudemys scripta troostii (Holbrook). Ecol. Monogr.,
20:32-54.
Christiansen, J.L., and R.R. Burken (1979) Growth and maturity of the snapping turtle (Chelydra serpentinn) i n
Iowa. Herpetologica, 35:261-266.
Emst, C.H., and R.W. Barbour (1972) Turtles of the United
States. The University Press of Kentucky, Lexington,
Kentucky.
Felger, R.S., K. Clifton, and P.J. Regal (1976) Winter dormancy in sea turtles. Science, 191:283-285.
Copeia, 3:314-318.
Gibbons, J.W. (1968) Growth rates of the common snapping
turtle, Chelydra serpentina, i n a polluted river. Herpetologica, 24:26&267.
Jackson, C.G., Jr. (1970) A biometrical study of growth i n
Pseudemys concinna suwanniensis. Copeia, 3:52%534.
Sexton, O.J. (1965) The annual cycle of growth and shedding
i n the midland painted turtle, Chrysemyspicta mrginata.
Copeia, 2:31&318.
Suzuki, H.K. (1963) Studies on the osseous system of the
slider turtle. Ann. NY Acad. Sci., 109:351-410.
Wilbur, H.M. (1975) A growth model for the turtle Chrysemys picta. Copeia, 2:337-343.
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