Journal of Reproduction and Fertility (2000) 119, 233–240
Ultrasonographic imaging of the testis and epididymis of the
bottlenose dolphin, Tursiops truncatus aduncas
F. M. Brook1, R. Kinoshita2, B. Brown3 and C. Metreweli4
1
Department of Optometry and Radiography, The Hong Kong Polytechnic University, Kowloon, Hong Kong; 2Zoological Operations and
Education Department, Ocean Park Corporation, Hong Kong; 3School of Optometry, Queensland University of Technology, Brisbane,
Australia; and 4Department of Radiology and Organ Imaging, The Chinese University of Hong Kong, Shatin, Hong Kong
Eight male bottlenose dolphins, Tursiops truncatus aduncas, underwent examination of
the reproductive organs to investigate the use of real-time B-mode ultrasonography
in assessment of reproductive status and to establish normal ultrasonographic
appearances. Ultrasonography allowed repeatable examinations which were well
tolerated by all animals. Ultrasonography was used to examine the testes, epididymides, vasa deferentia, penis, bulbourethral and bulbocavernosal muscles; the
prostate was not convincingly distinguished from surrounding muscles. Testicular
echopatterns and size differed among individuals. Three distinct testicular
echopatterns were discerned and could be used to differentiate males of different
reproductive status. Ultrasonographic appearance of the testes provides useful data in
assessing the reproductive status of male dolphins.
Introduction
Real-time B-mode ultrasonography is a non-invasive highly
sophisticated diagnostic method, which has a proven and
particularly valuable role in morphological description and
physiological evaluation of reproductive events. To date,
there is no known hazard associated with ultrasonography
used at standard diagnostic power levels (American Institute
of Ultrasound in Medicine, 1988; Hykes et al., 1992). Over the
past decade, the clinical application of ultrasonography in
veterinary medicine and animal reproduction has expanded
dramatically and its value in managed breeding of domestic
species is extensively documented (Ginther and Pierson,
1984, 1989; Buckrell, 1988; Pierson and Ginther, 1988; Squires
et al., 1988; Taverne and Willemse, 1989; Kahn, 1994).
Until fairly recently, the application of ultrasonographic
imaging to the study of reproductive physiology in wild and
exotic species was considered to be ‘in its inception’ (Lasley,
1985; Griffin and Ginther, 1992). Nowadays the use of
ultrasonography in the reproductive management of zoo
animals has increased and it has provided a needed research
tool for examining reproductive biology in exotic and
endangered species. Ultrasonographic imaging of the
reproductive tract has been reported in several large nondomestic species (Adams et al., 1991).
The bottlenose dolphin, Tursiops truncatus gilli or aduncas,
has been maintained since 1914 and is the most common
small cetacean seen in oceanaria. Today, improved husbandry
techniques have allowed dolphins in these facilities to be
trained to co-operate in routine medical procedures, enabling
collection of blood, urine and faecal samples, saliva and
Revised manuscript received 11 January 2000.
respiratory tract secretions, and even vaginal smears for
cytology (Streatfield and Chapman, 1976; Sawyer-Steffan and
Kirby, 1980; Cornell et al., 1987; Walker et al., 1988; Schroeder
and Keller, 1989; Kirby, 1990). These techniques have
contributed to the health of dolphins in captivity. Some have
also provided data on the reproductive physiology of the
species, but none provide a means of direct assessment of
events or changes in the gonads of live dolphins.
Although dolphins can also be trained to co-operate
in ultrasonographic examination (Brook et al., 1991), the
application of this technique in assessment of the
reproductive status of this species has been limited and
mainly confined to assessment of pregnancy (Stone, 1990;
Williamson et al., 1990; Taverne, 1991; Stone et al., 1999).
Stone (1990) reported that ultrasonography can demonstrate
the testes in dolphins and Briggs et al. (1995) used
ultrasonography to monitor changes in the testes of ten T.
truncatus in a study to evaluate the effects of leuprolide
acetate (Lupron®) on testicular size and function. None of
these reports describe the ultrasonographic anatomy of the
reproductive tract in detail.
Materials and Methods
Animals and management
Eight male T. truncatus aduncas from Taiwan or Indonesia
were investigated; seven males had been in the facility for
more than 4 years, but exact ages were unknown. Age
assessments and estimates of maturity were made from body
length and weight and external characteristics. Four males
were designated mature and two immature, and there was
© 2000 Journals of Reproduction and Fertility Ltd
0022–4251/2000
234
F. M. Brook et al.
uncertainty about the maturity of one animal. The eighth
male was a captive-born 2-year-old calf.
Each animal was weighed and measured at the beginning
of the study. Measuring and recording of body length and
weight is a routine part of the medical care protocol at this
facility and is performed using a suspended sling that can be
lowered into the water. Body weight is rounded up to the
nearest kg. Body weights recorded at the beginning of the
study are shown (Table 1).
Diet consisted of different proportions of capelin, sardine,
herring and smelt; the calf was also suckling. The holding
pool facilities consisted of several outdoor tanks. Males were
separated from females at the time of this study; however,
the structure of connecting gates between the tanks allowed
visual and auditory contact, although tactile contact was
limited.
Equipment
All examinations were performed with an Aloka 630 SSD
ultrasound unit (Aloka Co. Ltd, Mitakashi, Tokyo) in
conjunction with a 3.5 MHz linear array transducer. This unit
is relatively small and mobile, and is easily moved to the
poolside. The monitor was mounted on a customized arm
(Industrial Promoting Co., Hong Kong), allowing it to be
manoeuvred across and down to the poolside for easier
visualization. The whole unit was protected from splashes
by a waterproof cover. The transducer was waterproofed by
insertion into a plastic sleeve containing acoustic gel, which
displaced any air and provided good acoustic contact. Plastic
taping secured the covering sleeve and extended up the
transducer cable, to ensure this was also waterproofed. All
examinations were recorded on videotape and thermalprinting paper (Sony Echocopier, Sony Products Ltd, Tokyo).
Ultrasonographic procedures
Although it is preferable for examinations to be performed
with the dolphin in the water, accurate measurements are not
always possible in this situation due to inevitable movement.
A repeatability study was conducted to compare the
accuracy of measurements performed both with the dolphin
in the water and lying in lateral recumbence on a wet foam
rubber mattress at the poolside. Six measurements were
made of each testis in four subjects. Measurements
performed with the dolphin out of the water were more
accurate (SD ⫾ 0.08 cm) than when the dolphin remained in
the water (SD ⫾ 0.52 cm). Therefore, all testis measurements
in this study were performed with the dolphins out of the
water. This did not have an adverse effect on any animal.
All cross-sectional measurements of the testes could be
made directly from the image display, using the in-built
electronic caliper functions. However, the maximum width
of the ultrasonographic field of view available was 10 cm
and it was not possible to take longitudinal measurements of
longer testes directly from the monitor image. By locating
each end of the testis and noting these points on the surface
of the skin, it was possible to make indirect measurements of
testicular length. The transducer was placed perpendicular
to the flank, at the level of the genital slit and moved dorsally
or cranially until the testis was located. The proximal and
caudal ends of the testis were identified, both points were
noted on the skin surface and the distance between them
measured. The same orientation of the transducer was
maintained throughout the procedure and the measurement
was completed between inhalations to minimize any error
induced by movement.
The entire testis was then examined in longitudinal section
and the testicular parenchyma carefully assessed and
recorded. At the widest part of the testis, the transducer was
rotated 90⬚ to show a cross-sectional image. This image was
captured in ‘freeze-frame’ on the monitor, and electronic
calipers were used to measure dorsoventral diameter, width
and circumference directly from the image. The volume of
each testis was determined using Lambert’s formula for an
ellipsoid: volume (cm3) = length ⫻ width ⫻ depth ⫻ 0.71. The
total testicular volume was derived from the sum of the left
and right testicular volumes. A full survey of the parenchyma
was made in cross-section, from the cranial to the caudal pole.
The same procedure was repeated for the contralateral testis.
Table 1. Body weight, length, estimated age and testicular size in eight male bottlenose dolphins, Tursiops truncatus aduncas, at
the beginning of the study (April 1990)
Dolphin
Body
weight (kg)
Body
length (cm)
Victor
Wiki
Bobbya
Marty
Mini
Molly
Bunbi
Dippera
123
116
146
121
114
93
76
75
210
208
232
215
206
202
192
181
a
Estimated
age in years
(estimated maturity)
20+ (M)
15+ (M)
10+ (M)
10+ (M)
6+ (?)
6+ (I)
6+ (I)
2 (date of
birth known)
Dolphins from Taiwan; the remainder are the smaller Indonesian type.
M: mature; I: immature.
Left testis
length (cm)
Left testis
volume
(cm3)
Right testis
length (cm)
Right testis
volume (cm3)
16.8
18.5
18.2
14.0
8.8
9.3
6.3
4.4
263.4
361.7
271.2
151.2
26.6
42.9
12.7
4.0
16.5
20.5
22.8
14.8
9.0
10.0
6.4
4.6
286.3
531.8
280.8
147.6
32.3
45.7
10.3
4.6
Ultrasonographic anatomy of male dolphin reproductive tract
Testicular measurements and parenchymal assessments
were performed between one and four times per month and
a total of 336 examinations were completed between April
1990 and January 1992.
Results
Dolphin testes are large and easily accessible by transabdominal scanning. They can be visualized lying longitudinally, immediately caudoventral to the kidneys (Fig. 1).
The appearance and size of the testes varied among
individual dolphins. Testicular length ranged from a
minimum of 4.4 cm in Dipper, to a maximum of 22.8 cm in
Bobby; the right testis was usually longer than the left.
Testicular volume ranged from 4.0 cm3 (left testis) in Dipper
to 531.8 cm3 (right testis) in Wiki. Testicular length alone
could not be used to assess testis size accurately: the longest
testis (22.8 cm in Bobby), was almost half the volume of the
largest testis (531.8 cm3 in Wiki) (Table 1).
Ultrasonographic appearance of the testes
The testes are elongated and the border of each is well
demarcated by the surrounding tunicae, which were
235
visualized as a single hyperechoic border to the parenchyma.
The testicular mediastinum was visualized as a prominent
hyperechoic linear structure, extending the full length of the
testis (Fig. 2). In cross-section, the testes are rounded (Fig. 3).
A single testicular vein could be identified running through
the medial parenchyma to the caudal extremity of the testis
(Fig. 2b,c). When the testis is large enough, the dorsal surface
abuts the hypaxialis lumborum muscle and the ventral
aspect rests on the rectus abdominus muscle (Fig. 3b,c). The
cranial aspect of the medial surface is covered by bowel and
the distal aspect rests against the urinary bladder. The urinefilled bladder is visualized as an ovoid anechoic structure
lying in the mid-line, between and slightly ventral to the
testes (Figs 3a and 4).
In transverse section, the hypaxialis lumborum muscle
can be seen to lie immediately adjacent or close to the testis
(Fig. 3). The echopattern and echogenicity of the hypaxialis
lumborum muscle is similar in all animals, regardless of size
or age, therefore these values were used as a reference
against which to assess the echogenicity of the testicular
parenchyma. Three distinct ultrasonographic patterns could
be discerned in the testes of different subjects and each was
assigned a grading.
Grade I. The testicular parenchyma presented a homogeneous ‘speckled’ echopattern of mid- to high-level intensity
Fig. 1. Diagram illustrating ventral view of male Tursiops truncatus aduncas reproductive tract at the level of the testes.
236
F. M. Brook et al.
Fig. 2. Longitudinal ultrasonograms (with line diagrams) of the testes in (a) a juvenile (caudal pole of testis to the left of the image), (b) a subadult (cranial pole to the left of the image) and (c) a mature (cranial pole to the left of the image) bottlenose dolphin, Tursiops truncatus aduncas.
Black arrowheads indicate the testicular mediastinum; black and white arrowheads indicate the testicular vein. B: bowel; Bl: blubber layer; Ep:
head of epididymis; M: muscle layer. Echogenic areas and comet-tail artefacts seen in (a) and (b) are due to bowel gas. Scale marks are in
centimetres.
(Figs 2c and 3c), and was isoechoic or slightly hyperechoic
compared with the hypaxialis lumborum muscle. There was
some evidence of parenchymal lobulation. This pattern was
seen in Wiki, Victor, Bobby and Marty; lobulation was
particularly prominent in the elderly male, Victor (Fig. 4). The
cylindrical shape of the testes was expanded at the distal
portion. Linear hyperechoic structures could be seen extending
from the mediastinum; these were more prominent in Wiki and
Victor (Fig. 4). Testes showing this echopattern varied between
14 and 22.8 cm in length. As both Wiki and Bobby were known
to be reproductively mature, a grade I appearance was
assumed to indicate reproductively mature testes.
Grade II. The ultrasonographic appearance of the
testicular parenchyma was less well defined than in grade I
testes. The parenchymal echopattern was homogeneous, but
Ultrasonographic anatomy of male dolphin reproductive tract
237
Fig. 3. Transverse ultrasonograms (with line diagrams) of the testes in (a) a juvenile (left testis), (b) a sub-adult (left testis) and (c) a mature
(right testis) bottlenose dolphin, Tursiops truncatus aduncas. B: bowel; Hlm: hypaxialis lumborum muscle; Ram: rectus abdominus muscle; Rec:
rectum; T: testis; Ub: urinary bladder. Scale marks are in centimetres.
less echogenic than the hypaxialis lumborum muscle (Figs 2b
and 3b). The mediastinum was similar in appearance to that
in the older males, that is well defined and hyperechoic;
however, no linear mediastinal extensions were seen. The
shape of the testes was more consistent, without the obvious
widening at the distal end (Fig. 2b). This appearance was
seen in two dolphins, Molly and Mini. Testes showing this
echopattern varied between 8.8 and 10 cm in length. As testis
size increased, the parenchyma became more echogenic. Ten
months after this study, left and right testis lengths in Molly
238
F. M. Brook et al.
Fig. 4. Longitudinal ultrasonogram (with line diagram) of the testis (T) and head of the epididymis (Ep) in
an elderly bottlenose dolphin, Tursiops truncatus aduncas. Lobular appearance of the testicular parenchyma
and branching extensions of the mediastinum are apparent. Arrowhead indicates testicular mediastinum.
B: bowel; Ub: urinary bladder. Scale marks are in centimetres.
had increased from 9.3 and 10 cm to 14.9 and 15.9 cm,
respectively, and testicular echogenicity was similar to that
seen in grade I testes. It was hypothesized that a grade II
appearance indicated sub-adult or maturing testes.
Grade III. These testes were small (testicular length 4.4–
6.4 cm). The shape of the testes and the appearance of the
mediastinum were very similar to those seen in grade II
testes. However, the testicular parenchyma was very different
Ultrasonographic anatomy of male dolphin reproductive tract
and was markedly hypoechoic in relation to the hypaxialis
lumborum muscle and poorly differentiated (Figs 2a and 3a).
This appearance was seen in Bunbi and Dipper. As Dipper
was known to be only 2 years old, this appearance was
assumed to indicate immature testes.
Ultrasonographic appearance of the epididymis
The epididymides were clearly visualized in each dolphin,
except for Dipper. The structure of the epididymis was seen to
alter along its length. The head of the epididymis is
identifiable as a triangular structure, abutting the cranial end
of the testis, and is isoechoic or hyperechoic compared with
the testicular parenchyma (Fig. 4). The body of the epididymis
shows the same echogenicity, and extends caudally along the
dorso-lateral aspect of the testis. It is triangular in cross-section
and one side is closely applied to the testis. The distal twothirds of the epididymis change in appearance, becoming
more hypoechoic. In this section, the tubular structure of the
epididymis becomes distinguishable, particularly at the distal
end, where it is highly convoluted.
In Wiki, Victor, and Bobby, rounded protrusions of
convoluted tubules could be seen adjacent to the epididymis
(Fig. 5). These were not distinguishable in other dolphins. The
tubules were hypoechoic and were 2–3 mm in diameter. The
caudal epididymidis was large in the older males, extending
1.5–3.5 cm beyond the caudal pole of the testis. In this section,
the diameters of the tubule sections were greater (3–5 mm).
239
On several occasions, these diameters were measured preand post-ejaculation, after manual manipulation for sperm
collection. Some tubules were seen to decrease by up to 2 mm
in diameter.
If required, it is not difficult to image the penis, retractor
muscles and the large bulbourethral and bulbocavernosal
muscles which surround the prostate, but it was not possible
to differentiate the prostate gland convincingly.
Discussion
Ultrasonography of the testis is a non-invasive technique
which is performed easily on trained dolphins. It gives
information about testicular size and structure in live
dolphins which is not available by any other means.
Although dolphin testes are intra-abdominal, they are large
and relatively superficial and are easily accessible for
ultrasonographic evaluation. The internal structure of the
testes and epididymides can be clearly demonstrated and
ultrasonographic appearances are consistent with anatomical
descriptions in the literature (Meek, 1918; Harrison, 1969;
Green, 1972). Ultrasonography can be used to measure
testicular dimensions and the diameter of the epididymal
tubules.
In this study, the ultrasonographic appearance of the testes
varied among individuals and it is proposed that this reflects,
and so can be used to indicate, the reproductive status of
individuals. The testes of juvenile and sub-adult dolphins are
Ep
Vm
Fig. 5. Ultrasonogram showing longitudinal section through the mid-epididymis (Ep) of a mature Tursiops truncatus
aduncas, showing apparent vasal mass (Vm) between black arrowheads. Scale marks are in centimetres.
240
F. M. Brook et al.
cylindrical in shape. Juvenile testes present a homogeneously
hypoechoic parenchymal echopattern, whereas sub-adult
testes show increasing echogenicity over time. This may be
due to the increasing diameter of the seminiferous tubules in
the growing testis. As these dilate, the walls separate and
more interfaces will present to reflect the ultrasound beam,
increasing parenchymal echogenicity. The presence of free
spermatozoa will also increase echogenicity. Mature testes are
homogeneous and moderately to highly echogenic. This is
the characteristic echopattern of mature testes seen in many
mammalian species (Cartee et al., 1986; Pechman and Eilts,
1987). In all dolphins examined in the present study, a
prominent hyperechoic testicular mediastinum was observed.
In mature males, a dilated tubular structure can be seen
abutting the distal two-thirds of the testis. Rounded
protrusions of this structure are visible in males that have
been mature for some time; these protrusions are not seen in
recently mature males. The ultrasonographic appearance of
this structure corresponds to gross anatomical descriptions
of the vas deferens in dolphins (Hepburn and Waterston,
1902; Meek, 1918; Ping, 1926; Matthews, 1950; Harrison,
1969). Harrison observed that the protrusions increased in
both number and size in older dolphins and this is consistent
with the ultrasonographic visualization of these structures
only in older males. However, only two vasal masses were
identified in any of the older males in the present study, one
on each side. Follow-up examinations of Molly revealed that
one vasal mass had formed on each side by June 1995, almost
5 years later. The presence of one or more of these
protrusions in a male Tursiops may be useful to identify an
animal that has been sexually mature for some years.
Ultrasonographic differentiation between the epididymis
and the origin of the vas deferens was not possible.
Tubule diameters at the distal end of the testis decreased
in diameter by as much as 2 mm after ejaculation. This
finding supports the hypothesis that the large vas deferens
allows storage of seminal fluid in the absence of seminal
vesicles in dolphins (Matthews, 1950), although further
study is required to confirm these results.
The support and technical assistance of the staff of the Zoological
Operations and Education Department, Ocean Park Corporation,
Hong Kong, and K.T. Luk of Industrial Promoting Co., Hong Kong,
are gratefully acknowledged.
References
Adams GP, Plotka ED, Asa CS and Ginther OJ (1991) Feasibility of
characterizing reproductive events in large, non-domestic species by
transrectal ultrasonic imaging Zoo Biology 10 247–253
American Institute of Ultrasound in Medicine (1988) Bioeffects
considerations for the safety of diagnostic ultrasound Journal of Ultrasound
in Medicine 7 51–53
Briggs MB, Van Bonn W, Linnehan RM, Messinger D, Messinger C and
Ridgway S (1995) Effects of leuprolide acetate in depot suspension on
testosterone levels, testicular size and semen production in male atlantic
bottlenose dolphins (Tursiops truncatus) IAAAM Proceedings 26 112–113
(Abstract)
Brook FM, Chow DCMA and Schroeder JP (1991) Ultrasound imaging of the
reproductive tract of the male bottlenose dolphin British Journal of Radiology
763 645 (Abstract)
Buckrell BC (1988) Applications of ultrasonography in reproduction in sheep
and goats Theriogenology 29 71–83
Cartee RE, Powe TA, Gray BW, Hudson RS and Kuhlers DL (1986)
Ultrasonographic evaluation of normal boar testicles American Journal of
Veterinary Research 47 2543–2548
Cornell LH, Asper ED, Antrim JE, Searles SS, Young WG and Goff T (1987)
Results of a long range captive breeding programme for the bottlenose
dolphin Zoo Biology 6 41–53
Ginther OJ and Pierson RA (1984) Ultrasonic evaluation of the reproductive
tract of the mare: ovaries Journal of Equine Veterinary Science 4 11–22
Ginther OJ and Pierson RA (1989) Regular and irregular characteristics of
ovulation and the interovulatory interval in mares Journal of Equine
Veterinary Science 9 4–13
Green R (1972) Observations on the anatomy of cetaceans and pinnipeds. In
Mammals of the Sea: Biology and Medicine pp 247–297 Ed. SH Ridgeway.
Charles C. Thomas, Springfield, IL
Griffin PG and Ginther OJ (1992) Research applications of ultrasonic imaging
in reproductive biology Journal of Animal Sciences 70 953–972
Harrison RJ (1969) Reproduction and reproductive organs. In The Biology
of Marine Mammals pp 253–348 Ed. HT Andersen. Academic Press, New
York
Hepburn D and Waterston D (1902) Anatomy of the genitourinary apparatus
of an adult male porpoise Proceedings of the Royal Physical Society, Edinburgh
Vol. XV 112–130
Hykes DL, Hedrick WR and Starchman DE (1992) Ultrasound Physics and
Instrumentation 2nd Edn pp 190–209 Mosby Year Book Inc., St Louis
Kahn W (1994) Veterinary Reproductive Sonography Schlutersche, Hanover and
Mosby Wolfe, London
Kirby VL (1990) Endocrinology of marine mammals. In Handbook of Marine
Mammal Medicine: Health, Disease and Rehabilitation pp 303–351 Ed. LA
Dierauf. CRC Press Inc., Boca Raton, FL
Lasley BL (1985) Methods for evaluating reproductive function in exotic
species Advances in Veterinary Science and Comparative Medicine 30 209–228
Matthews LH (1950) The male urogenital tract in Stenella frontalis (G. Cuvier)
Atlantide Report 1 223–247
Meek A (1918) The reproductive organs of the cetacea Journal of Anatomy 52
186–210
Pechman RD and Eilts BE (1987) B-mode ultrasonography of the bull testicle
Theriogenology 27 431–441
Pierson RA and Ginther OJ (1988) Ultrasonic imaging of the ovaries and
uterus in cattle Theriogenology 29 21–32
Ping C (1926) On the testis and accessory structures in the porpoise Anatomical
Record 32 113–117
Sawyer-Steffan JE and Kirby VL (1980) A study of serum steroid hormone
levels in captive female bottlenose dolphins, their correlation with
reproductive status, and their application to ovulation induction in
captivity US Marine Mammal Commission Report Contr. MM7AC016
Schroeder JP and Keller K (1989) Seasonality of serum testosterone levels and
sperm density in Tursiops truncatus. Journal of Experimental Zoology 249
316–321
Squires EL, McKinnon AO and Shideler RK (1988) Use of ultrasonography
in reproductive management of mares Theriogenology 29 55
Stone LR (1990) Diagnostic ultrasound in marine mammals. In CRC Handbook
of Marine Mammal Medicine: Health, Disease and Rehabilitation pp 252 Ed. L
Dierauf. CRC Press Inc., Boca Raton, FL
Stone LR, Johnson RL, Sweeney JC and Lewis ML (1999) Fetal
ultrasonography in dolphins with emphasis on gestational aging. In Zoo and
Wild Animal Medicine. Current Therapy 4 4th Edn pp 501–506 Eds Fowler and
Miller. WB Saunders Company, Philadelphia
Streatfield MM and Chapman CG (1976) Staphylococcus aureus infections of
captive dolphins (Tursiops truncatus) and oceanarium personnel American
Journal of Veterinary Research 37 303–305
Taverne MAM (1991) Applications of two-dimensional ultrasound in animal
reproduction Wiener Tierarztliche Monatsschrift 78 341–345
Taverne MAM and Willemse AH (1989) Diagnostic Ultrasound and Animal
Reproduction Kluwer, Dordrecht
Walker LA, Cornell L, Dahl KD, Czekala NM, Dargen CM, Joseph B, Hsueh
AJW and Lasley BL (1988) Urinary concentrations of ovarian steroid
hormone metabolites and bioactive follicle-stimulating hormone in killer
whales (Orcinus orcus) during ovarian cycles and pregnancy Biology of
Reproduction 39 1013–1020
Williamson P, Gales NJ and Lister S (1990) Use of real-time B-mode
ultrasound for pregnancy diagnosis and measurement of fetal growth rate
in captive bottlenose dolphins (Tursiops truncatus) Journal of Reproduction and
Fertility 88 543–548