SOME INFORMATIONS ON THE GROWTH OF THE
GANGES DOLPHIN WITH A COMMENT ON THE
INDUS DOLPHINTOSHIO KASUYA *ABSTRACT

Following result was obtained in the study based on the 22 Ganges dolphins obtained in East Pakistan. Though the parturition season lasts long
period, there might be two peaks in early winter and in early summer. Calf isborn at small size compared with that of oceanic dolphins. The female grows
larger, but the weight is slightly smaller than the male of same body length,
which will be related with the larger length of the female snout. The sexualand physical maturity seems to be attained at the age of about 10 or less, andmore than 20 years respectively. The growth pattern of this species shows
peculiarities.
From some morphological differences, it is proposed to deal the Ganges
and Indus dolphins as two separate subspecies.

INTRODUCTION

When seen from the evolutional point of view, the freshwater dolphins or Platanistidae is a interesting group of toothed whales in the morphological primitivenessfound together with some specialization, and the restricted habitat.
Various authers have conducted the morphological and anatomical studies on
Platanista, especially Pilleri and his colleagues are conducting the study on Platanista
in various field of the biological science. They will throw light on the evolution of
Platanistidae.
Present study deals with the problems related with the growth and reproductionof Platanista, which will afford some of the fundamantal informations on the adaptation and specialization of the toothed whales.
MATERIALS

This study is based on the 22 individuals of the Ganges dolphin obtained or studied
by the Cetacean Research Expedition, University of Tokyo, directed by Prof. M.
Nishiwaki. These materials are shown in Table 1 together with some biologicalinformations. As shown in Fig. 1, all the present specimens were caught in East
Pakistan, present Bangladesh. Among these specimens, no. 14 is a fetus obtained at
the lower Meghna and preserved at East Pakistan Fish. Res. Inst. in Chandpur,
which external measurements were made by M. Nishiwaki, 5 were caught at the Kola
River a tributary of the Jamuna River in the north of Tistamukhghat, 11 at the* Ocean Research Institute, University of Tokyo, Tokyo.
Sci. Rep. Whales Res. Inst.,
No. 24, 1972, 87-108.

KASUYA88
TABLE 1.

LIST OF MATERIALS USED IN THIS REPORT

Date of death

No.

Date of catch

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

12, x, 1969
12, x, 1969
- , VI, 1969
- , VI, 196923, VIII, 1969 23, VIII, 196930, XI, 196930, XI, 1969
20, X, 1969
20, x, 1969
20, XII, 1969
28, XII, 19696, I, 1970
6, I, 197012, I, 197012, I, 197012, I, 197012, I, 1970
19, I, 1970
19, I, 1970
26, I, 197027, I, 1970
26, I, 1970
26, I, 1970
1, II, 1970
1, II, 1970
27, VIII, 1967 27, VIII, 1967
26, I, 1970
9, IV, 1970

6
6
6
6
6

16

26, I, 1970~

1726, I, 197013, IV, 1970
2, VII, 1970

Sex

6
6
6
6
~

~

6
6
~
~

~

18
19
20
21

28, IV, 1970

28, IV, 1970-, v, 1970
7, v, 1970-, v, 1970
7, v, 1970

6
6

8, VI, 1970

8, VII, 1970~22

26, I, 197030, VII, 1970

6

~

Body
length
(cm)
105.0
100.5
115.0
171.5
110.0
117.0
113.0
121.5
117.5
200.0
113.0
115.0
115.0
27.0
114.0*
118.0
120.0*
120.5
120.0*
127.0
126.0
122.0
199.0
67.4*
76.0
122.0*
126.0

Body
weight(kg)

Position of capture
Sutiakhali, Brahmaputra

18.8

14.5

16.8

Kalir Bazar,
Begunbari,
Kewatkhali,
Khagdahar,
Jamalpur," MaghnaLalpur,Kola river
Bhairab Bazar, Meghna
Chandpur
Kola river

16.4
Kola river
17.0
Kola river
23.0
17.0
22.5
84.0
?7.3*
3.4

Dighirpur, Meghna
Bhairab Bazar, Meghna
E.P.A.U., Brahmaputra
Bhabakhali, Brahmaputra
Kola river

24.0* Measured at the time of capture.

Brahmaputra River, and 5 at the Meghna River near Bhairab Bazar.
One of the method used in catching these animals is the "Jagatber" usuallyoperated in dry season (Kasuya and Haque 1972). Specimens nos. 8, 9, 11, 15, 16,
17 and 22 were obtained by this method. Some of other specimens were caught withdrag net which instruments are shown in Pl. I, Fig. 2 in Kasuya and Haque (1972).
Specimens nos. 15, 16, 17, and 22 were transported to Japan and kept alive inan aquarium, The Kamogawa Sea World, for several months. No. 21 was kept
alive in a pond at Mymensingh for one month, then the carcass, together with nos.
18, 19, and 20, was transported to Japan by Prof. A. K. M. Aminul Haque.
AGE DETERMINATION AND GROWTH

Age characteristics
In this species, the growth layers are observed on both tooth and scapula.
On the scapula, there are observed several narrow translucent bands arranged
parallel with the contour of the dorsal edge. In the younger individuals less than 2
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

89

GROWTH OF THE GANGES DOLPHIN-- _.,.._ - - - _.....,

.,,,.

~

-

r- -,

," .... J,- - ..,,/

'

..,
\

I

''\

I I '
I I
\I
\
'-'

l

Fig. 1. Map of the Ganges and Brahmaputra River system showing the positions of
the catch of present specimens. Numbers in the map indicates the specimen number
in Table 1. (For Baria! read Barisal.)

years old, the band is clear and the number coincides with that of growth layers in
dentine and in cement. But, in the older individuals, the bands formed in theyounger stage become vague or disappear, because they are covered by the bone
tissue as the thickness of scapula increases.
In the cross section of the tooth, both in dentine and cement, there are observed
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

KASUYA

90

wider opaque layer and narrower translucent layer accumulated alternately (Pl. I).
As the number oflayers in dentine and cement nearly coincides, it is considered thatthey are formed in a same cycle. However, as the growth layers in dentine is moreregular in thickness and easily counted than the layers in cement, I concluded thatthe best age characteristics of Platanista is the dentinal growth layers, which is used in
the present study.
For preparing the tooth for age determination, a larger tooth removed from theanterior part of maxilary or mandibular tooth row was ground perpendicularly fromboth sides to the thickness of about 50 to 70 µ (Kasuya 1972).
For determining the age, the number of the opaque layers in dentine wascounted under the microscope. In the younger individuals, the age was determined
into the approximate l /4 year intervals considering the thickness of the first and last
opaque or translucent layers. The dentine formed in fetal stage, an opaque layer,
was not included. Several thin darker dentinal layers often observed in the layer oflate fetal stage or in the first postnatal opaque layer are not discussed here. In thisstudy, though the accumlation rate of the growth layers is not concluded, it is presumed from the consideration of the last layer (Table 2) that the translucent layer
TABLE 2. CONDITION OF THE NEWEST LAYERS IN DENTINE OF THE
GANGES DOLPHIN, SHOWING THE SEASONAL ALTERNATION OF
THE OPAQUE AND TRANSLUCENT LAYERS
OpaqueMonthTranslucent
Thin

3

January
April
May
June
.July
AugustOctoberNovember
December

TABLE 3.

Age

0.25
0.50
0.75
1.00
1.25
1.50
1.75
10
16

28

Thick

3

3

1

2

AGE OF THE GANGES DOLPHIN PRESUMED FROM THE
GROWTH LAYERS IN DENTINE
No. ofsamplesl2
9Range of bodylength, Sex76.0, ~
100.5, <!
105.0-110.0, ~ <!
113.0-117.5, ~ <!
122.0, <!
120.0, ~126.0, ~171.5, <!
200.0, <!
199.0, <!

Mean bodylength (cm)

107.5
116.2
} 122.7

Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

91

GROWTH OF THE GANGES DOLPHIN(clear band) will be formed in winter and the opaque in summer as in the case of theoceanic dolphins (Sergeant 1959, '62, Kasuya 1972). The result of the age determination based on the growth layers in dentine is shown in Table 3.
The growth of the tooth of the Ganges dolphin has a peculiarity. Namely, theincrease of the length of tooth after the formation of the root, which is considered tobe finished at the 4th year after birth, is carried on by the accumulation of the thickcement layer (Pl. I). This type of growth is quite different from that observed in
the tusk like tooth of the sperm whale, but can be explained as a result of specialization of the tooth of delphinidae, where the accumulation of cement layer is thinner.
The accumulation of the dentinal layers continues after the formation of the root.
And even in the oldest individual, in which 28 dentinal layers are counted, there isobserved the space for more accumulation of dentine in the dental cavity.
120
E

u110
c
.c100
Ol

jj 90
~80
0
ro

70 ..... .

/60~~~~~-~~~~~~~~~~~~~~~~~~

12 1 2 3 l.

5 6 7 8 9 10 11 12 1 2 3 l.
Month

5 6 7

Fig. 2. Presumed mean growth curve of the Ganges dolphin. Closed circle indicates
male, open circle female, and cross marks the mean body length at the age of0.5, 1
and 1.5 year based on the growth layers in dentine. Circles connected with astraight line indicate the body length at the time of capture and that at death. The
dotted lines indicate the range of known largest fetus and smallest calf.

Growth in young stage
Among the present specimens, the youngest individual was 67.4 cm (No. 21) at
the time of capture. This individual is considered to be just after the birth. Anderson (1878) reported a fetus of 70.5 cm in body length. Therefore, at present, bodylength of the Ganges dolphin at the time of birth is presumed to be about 70 cm.
Besides the age determination data based on the dentinal layers, following informations on the growth of the Ganges dolphin were obtained. The specimen
no. 21 showed the growth of8.6 cm in body length while it was kept alive in a pondfor one month. And the 3 specimens in the 4 animals kept alive in an aquarium,
excluding one which had no increase of the length, showed the average growth of
I.I cm per a month (Table 1). Furthermore, the body length of the juvenile individuals shows a slight increase with the elapse of date of catch.
The growth curve of the Ganges dolphin, shown in Fig. 2, was drawn based on
the above informations. According to this curve the animal attains the body length
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

92

KASUYA

116 cm at one year after birth, or the increment of65.7% of the length at the birth.
As shown in Pl. II, only the anterior teeth of upper and lower jaws had slightly
erupted in the specimen no. 21. This will indicate that this animal was suckling at
the time of capture. Within a month when this animal was kept alive, however,anterior 16 pairs of tooth of the both jaws erupted. And the observation of thestomach of this animal showed that it had started the feeding on fish. All theother juvenile individuals ranging from 110 cm to 120 cm in body length, caught in
the river, had the food in the stomach and most of their teeth had already erupted.
And these individuals were considered not to be accompanied by the mother.
From these informations it is presumed that the calves born in the early winterstart feeding at 1 or 2 months after birth, and weaning will be accomplished by the
beginning of the dry season, or within one year after birth.

Sexual maturity
As shown in Table 4, all the individuals smaller than 130 cm in body length aresexually immature.
TABLE 4.

SEXUAL CONDITIONS OF THE GANGES DOLPHIN

Body length
(cm)

Sex

110.0-126.0
115.0-121.5
171.5
199.0
200.0

6
6
6
6

~

Sample
size
3
4

Age

<2
<2
10
28
16

Gonadsweight (g)0.4-1.6
6.7-7.5250
1110

Maturity
immature
immature
probably mature
maturematureA male specimen no. 20, 199 cm in body length, was identified sexually matureby the histological observation of the testis. Though the testes were too decomposed
for the histological observation, no. 20, 200 cm in body length, was considered fromthe weight of testes to have attained the sexual maturity. In the specimen no. 4,
the testes had decomposed too bad to weigh, but the size of the original testis waspresumed from the size of tunica to be a half or a third of that of no. 10. Then, theweight of the testes of this individual might have been from 40 to 140 g, which is far
heavier than those of immature animals, and suggests that this individual had probably attained the sexual maturity or puberty.
This presumption lead to the conclusion that the male Ganges dolphin may
attain the sexual maturity at about 10 or slightly less years as in the case of othertoothed whales (Kasuya 1972, Ohsumi et al 1963, Sergeant 1962), and at the bodylength about 170 cm or less.
There are 6 records of sexually mature females known to me (Anderson 1878,
Pilleri 1970), among which the smallest individual is 200 cm in body length. And
the largest immature female is 150 cm (Anderson loc. cit.). These informations
suggest that the sexual maturity will be attained between 150 cm and 200 cm. But as
the female seems to attain larger size, it will be better to consider that the femaleattains the sexual maturity between 170 and 200 cm in body length.
Sci. Rep. Whales Res. Inst.,.No. 2'1, 1972.

GROWTH OF THE GANGES DOLPHIN

93

Physical maturity
None of the present specimens had attained physical maturity. Table 5 shows
the relation between body length and the ankylose of vertebral epiphysis to the centrum observed after cleaning the skeleton. The anterior epiphysis ankyloses earlier
than the posterior one on the same vertebra. The epiphyses of the posterior thoracic
vertebrae seems to be the last which ankyloses to the centrum.
TABLE 5.

ANKYLOSE OF VERTEBRAL EPIPHYSES TO THE CENTRUM IN
THE MALE GANGES DOLPHIN1 »2 >No. of vertebrae 1 2-----_Cl
Speci- Body
men length Age
no.
10
20
4
13

3 4

5 6

7

8 9
Dl

10 11 12 13 14 15 16 17±± + + ++++++++ + ++++++++ + ± + ± + ± ± 199.0 28 +++++++ ++++++++ ±171.5 10 +++ ± ±±+126.0 1.75 +++--

200.0

16

18 19 20 21 22 23 24 25
Ll++++ + +++± +++ + ± +±++

1>

The upper lines indicate the anterior epiphyses, and the lower the posterior.
•> + indicates the ankylosed epiphysis, ± that ankylosed at small parts, and - free epiphysis.

The male specimens nos. 10 and 20 are physically immature in spite of the ageof 16 and 28 years old respectivily, which suggests that the growth of this species continues longer period than Stenella caeruleoalba (Kasuya 1972) and probably than
G!obicephala melaena (Sergeant 1962), as in the case of Physeter catodon (Nishiwaki et al
1958, Ohsumi et al 1965).
Anderson (1878) reported a physically mature 211 cm male, and the present
specimen no. 10 is supposed to may have attained the physical maturity within ashort period. These informations suggest that the body length of male at the attainment of physical maturity is between 200 and 210 cm.
In the present study, no physically mature female was obtained. The largest
male known to me is 211 cm in body length (Anderson Zoe. cit.), but there are several
records of female larger than this male, or 226, 238, 240 and 252 cm in body length(Anderson Zoe. cit., Pilleri 1970). Among these records the 238 cm female is physically immature but the 252 cm female is physically mature. Then the best estimation of the body length of the female at the attainment of physical maturity may, atpresent, be probably about 250 cm, which is larger than that of the male.
BREEDING SEASONIn the present study sufficient number offetus was not obtained to analize the breeding season. However, the dates of birth of the juvenile individuals were presumed
from the body length and date of catch, using the mean growth curve in Fig. 2. This
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

94

KASUYATABLE 6. DATE OF BIRTH OF JUVENILE INDIVIDUALS PRESUMED FROM THE
BODY LENGTH AND GROWTH CURVE, AND RECORDS OF LARGE FETUS
OF GANGES DOLPHIN.
Month
No. of birthl>
Large fetus 2 >
1
2

IX

x

XI

XII

I

II

III

3

2

2

3

2

3

IV

v

1

0

VI

2

> Calculated from present specimens.
> Cited from Anderson (1878).

resut shows that most of the juvenile individuals were born from October to Marchwith a center in December and January (Table 6). So, it is considered that thisseason is, at least, one of the parturition seasons of the Ganges dolphin, which coincides with the beginning of the dry season and with the winter season when most of
the dolphins in the small rivers move to the main streams (Kasuya and Haque 1972).
However, as indicated by specimen no. 21 of present study and four 25 cm fetuses in
December reported by Pilleri (1970), another peak of parturition in the beginning ofsummer season (Anderson 1878) can not be denied. Anyway it seems to be sure thatthe parturition of this species can occur at any season of the year, and the presumed
two peaks are not conspicuous.
If there are two peaks in the parturition season, one in the early winter and theother in the early summer, as in the case of Stenella coeruleoalba (Kasuya 1972), thegestation period may probably be about one year. And the 27 cm fetus in August(no. 14) might have been born in the former season and those reported by Pilleri(loc. cit.) in the latter. In this case, it must be presumed that the calves born in theearly summer would have left, accompanied by the mother, the small streams in
September when the water starts to decrease, and that some of the calves born about ayear before and newly weaned had failed to leave the small streams where most of thejuvenile specimens were obtained in the present expedition.
BODYWEIGHT
Fig. 3 shows the relation between body length and weight in the Ganges dolphin(circles) and the Indus dolphin (Cross marks), including 12 data cited from Pilleri(1970). As seen in Fig. 3, the body weight of the adult female is slightly smaller thanthat of the male of same body length, but there is no sexual difference in juvenile individuals. This will be related with the sexual dimorphism mentioned in the next
chapter.
The regression line, calculated by the method of least squares for all the femalesof the Ganges d0lfbin except the smallest specimen (no. 21) is shown by the formula
W =0.0003025 L2· 290 , where L means body length in cm and W body weight in kg.
The formula for the Ganges dolphin of adult males and the juveniles of both sexes
except no. 21 is shown by W=0.00002456 L 2 ·S 26 •The body weight of the smallest fem ale is smaller than the value expected fromthe formula, this will probably due to the unfavorable condition of the animal in theSci. Rep. Whales Res. Inst.,

No. 24, 1972.

GROWTH OF THE GANGES DOLPHIN

95-.I::.100Clc..!! 50>-"O0m
4 6 1020
40
Body weight in kg2

100 200

Fig. 3. Relation between body length and body weight in the Ganges dolphin.
Closed circle and solid line indicate male, and open circle and dotted line female.
Cross mark indicate the lndus dolphin reffered from Pilleri (1970). For explanation see text.
TABLE 7.
Specimen no.
Body length (cm)Sex
Body weight (kg)Weight of parts
Blubber
blubbertail flukes
Skeletonskullvertebraeribs
scapulaeflippersll
Skeletal muscle
vertebral, dorsal
vertebral, ventral
ma5seterothersInternal organs
Total

WEIGHT OF THE GANGES DOLPHIN

21
76.0

19
122.0

18
126.0

~

J

J

J

3.42

22.5

17.0

84.0

g

%

970

30.0

1,175
558
365
130
32
90
418
192
80

36.3
17.3
11.3
4.0
1.0
2.8
12.9
5.9
2.5

146
670
3,233

4.5
20.7
100.0

20
199.0

g

%

g

%

g

%

10,600
10,220
380
3,670
1,210
1,430
560
120
350
5,881
2,720
1,620
410
1,131
1,724
21,875

48.5
46.7
1.7
16.8
5.5
6.5
2.6
0.5
1.6
27.3
12.4
7.4
1.9
5.2
7.9
100.0

5,280
4,880
400
3,723
1,640
1,150
503
100
330
5,255
1,800
850
205
2,400
1,390
15,648

33.7
31.1
2.6
23.8
10.5
7.3
3.2
0.6
2.1
53.6
11.5
5.4
1.3
15.3
8.9
100.0

30,99029,1401,850
16,050
5,630
5,170
2,230
540
2,480
29,79011,4406,190
R. 71011,4509,578
86,408

35.9
33.7
2.1
18.6
6.5
6.0
2.6
0.6
2.9
34.5
13.2
7.2
0.8
13.2
11.0
100.0

1 > Including the blubber.

pond where this animal was kept alive to die.
Table 7 shows the proportional weight of organs of 4 Ganges dolphins. In thisspecies the weight of blubber occupies high percentage of from 30 to 48 % of bodyweight, and the internal organs do only from 8 to 20 %· The ratio of skeletal muscle,
which increases with the growth of the animal, is from 12 to 35 %of the body weight.
In the specimens nos. 18, 19 and 21, the total weight calculated by summing up
Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

KASUYA

96

TABLE 8. THICKNESS OF BLUBBER MEASURED ON THE LATERAL LINE,
LOWER COLUMN INDICATES THE SOFT FATTY TISSUE BENEATH
THE DERMIS.
Specimen
Body length (cm)
Sex

21
76.0

7
113.0

6
117.0

9
117.5

8
121.5

19
122.0

20
199.0

10
200.0

<1

<1

<1

<1

<1

~

<1

<1

cm

% cm

% cm

0.5
0.6
Level of flipper
0.5
0.0
Level of dorsal fin 0.4
0.2
Level of umbilicus 0.5
0.3
Level of anus
0.3
0.1

0.7 1.2
0.8 2.0
0.7
0.0
0.5 2.5
0.3 0.0
0.7 1.5
0.4 1.0
0.4 1.0
0.1 0.0

Level of neck

1.1

1.8

% cm

% cm

% cm

1.0 0.9
3.0 2.6
1.1 0.9
1. 7 1.5

2.2

1.3

o.o

1.1

1.3
0.9
0.9
0.0

1.5 1.3 1.2 1.0 1.1 0.9
2.7 2.3 0.9 0.8 1.9 1.6
1.5 1.3 1.6 1.4 1.9 1.6
0.0 0.0 0.0 0.0 0.0 0.0% cm% cm %

2.0 1.0
0.5 0.3
1.1 2.5 1.3
0.9 1.5 0.8
1.8 0.9
0.8 0.4
2.2 1.1
0.8 0.4

1.5
3.3

0.8
1.7

3.2
0.0
1.8
2.0
2.5
0.0

1.6
0.0
0.9
1.0
1.3
0.0

the weight of each parts shows the decrease of from 2.7 to 8.2 %of the original weightweighed before dissection. However, in case of no. 20 which was dissected watering
to defrost, the summed weight showed the increase of 2.4%.
Table 8 shows the thickness of blubber measured on the lateral line. The
blubber of this species is characterized by the thick soft fatty layer beneath the harderconnective tissue which will probably correspond to the blubber observed in theoceanic cetacea.
RELATIVE GROWTH
All the measurements, except those of appendages and distances between ear, eyeand angle of gape, and the length of nasal slit, were made on a tape set in parallelwith the carcass. These measurements of the present specimens are tabulated inAppendix. The relative growth of the anterior region of the Ganges dolphin is shownin Figs. 4 and 5, and that of posterior region and appendages in Figs. 6-8 and Table 9.
Some important measurements are summarized in Fig. 9.
The length of head region is larger in adult females than in the males of corresponding body length. This is due to the larger length of the female rostrum assuggested by Anderson (1878), and will mean that after the growth of rostrum finished in the male the growth of this region continues in the female to attain about 20
cm larger length. This sexual dimorphism is presumed to come out at about 150 cm
in body len~th. .\s the position of the anterior insertion of flipper does not show thesexual difference, the length from center of eye to anterior insertion of flipper is considered to be slightly larger in adult males than in the females (Fig. 4, top). Though
the rostrum and mandible of juvenile Ganges dolphin is nearly straight, those tips ofolder individuals of both sexes are bended obliquely upward. This feature is wellshown in Pls. 39 and 40 of Anderson (1878).
The relations between body length and the dimensions of the posterior region,
Sci. Rep. Whales Res. Inst.,

No. 24, 1972.

97

GROWTH OF THE GANGES DOLPHIN

and those of appendages are shown by straight lines. The regression lines in Figs. 6-8
and " mean " in Table 9 are calculated for the Ganges dolphin by the method ofleastsquares. Among these measurements, those concerning the positions of umbilicus
and genital aperture show the sexual dimorphism. In the male, umbilicus situatesslightly anteriorly than it does in the females. This will be related with the extremely anterior situation of the male reproductive aperture, which situates very close to theumbilicus as in the case of Pontoporia blainvillei (Table 10). Though the measurement
is not recorded, it is clear that the male gential aperture of Inia opens near to the umbilicus same as Pontoporia and Platanista (Pilleri 1969, Fig. 3). So, it is presumed that
this character may be general in Platanistidae. But similar character is observed alsoin Physeter and Kogia.

Tip of rostrum to angle of gape.

6i:----------A.

, "'" .,. ......

40

..

~ ~.
co·.~§

20____-·

~

0

·~

O

~·"""
I

50

I

0

I

I

100

150
200
Body length (cm)I

250

Fig. 4. Relative growth of the anterior region in Platanista. Circle indicates present
specimen of the Ganges dolphin, triangle the Ganges dolphin reffered from Anderson(1878) and Pilleri (1970), square the Indus dolphin reffered from Pilleri (1970).
The closed marks and solid line indicate male, and open marks and dotted line
female. Lines are drown by eye for the Ganges dolphin.

DISCUSSION ON THE GROWTH
Though, in the present study, no definite conclusion on the parturition season was
Sci. Rep. Whales Res. Inst.,

No. 24, 1972.

98

KASUYAobtained, the possibility was suggested to consider that Platanista has two parturitionseasons one in early winter and the other probably in early summer. Then, thebreeding season of this species seems to retain the same pattern as that of Stenella
caeruleoalba which is different from that of Physeter, Phocoena, or Delphinapterus (Kasuya1972).
Ohsumi (1966) showed an allometric relationship, B=0.532 M 0 · 916, between
mean body length at birth (B in m) and that offemale at the attainment of sexual
maturity (M in m) for Physeter, Beradius and several species of Delphinidae. If thisformula is applied for Platanista assuming B=0.70 (m), 135 cm is obtained as the
cm .... Tip of rostrum to nostril
40'"
....

20'"
Length of nasal slit/~··

Tip of rostrum to ear

oo"/

t;: 0

t-

20

0

•

E:.~~:'-e-··-4=--4'9-·-.--~- . - o - - · • o•i':.
tpt""

o

01--1-~--1~~L-~..l-~....L.-~-'-~-'-~--'-~--''--~"---t-...

Tip of rostrum to eye

4, ......

•• ----•, , ' lJ.

I

50

100

I

I

150

I

I

200

250

Body length (cm)Fig. 5.

Relative growth of the anterior region in Platanista.

For marks see Fig. 4.

female body length at the attainment of sexual maturity. However, this figure is too
smaller than the length obtanied in this study, even if it is compared with the smaller
sex or the male.
The increment of body length of Platanista in the first one year after the birth is
65. 7 % of the body length at birth. This is nearly same with the value seen in someDelphinidae species (Kasuya 1972), and it is considered that the growth pattern of
Platanista in the early stage of life retains presumable primitiveness as in the case of
Sci. Rep. Whales Res. Inst.,

No. 24, 1972.

GROWTH OF THE GANGES DOLPHIN

99

some Delphinidae species. Then it is considered that the augmentation of body size
may have happened in the later part of the growth as one of the specialization of
Platanista.
Accompanied with the augmentation of body length, the elongation of thegrowth period may have brought on as in the case of Plryseter. But these specialization of growth is considered to have been accomplished as a result of evolution occured independently of that of oceanic odontoceti. Though in the oceanic species
the secondary sexual characters as the tooth, or size or proportion of body develops
usually in the male with an exception of body length of some Ziphiids, in Platanista
cm Umbilicus to anus

• ._-

~~

-~------·-.
........-·v·~ . . . . . . . --- __20 ~:-ooo!;,•,...._ _._•_,,.,. .........

110 .•o- ----___..___ _ __ ___,__
_._

___..

......_/ .___/,,,~-o ..............

. ,'Tail notch to umbilicus •,'',:t/!!6
,'

,''

90

,''

,,,,''

70

,-'

..

Jtlr:! 0

•' ,,

,'

,o

•

••• ,'o• Et>' 0,' ,•' .··
,'

••

,'

.
a

D

:~~ 0•

,

50

,'

•

0

,,'
, o'

.·

,,·,·'

,•'

•

...

Tail notch to anus

Ill' 0/09•..-','..··/·

30..y.··_,·· ......
0,-~_:..

··· _10 -::i.:..:---"

50

0

.

•

_

••

~

•...!.o~~'!'!;J--Tail notch to ant. ins.
of tail fluke

100

150

200

250

Body length (cm)Fig. 6. Relative growth of the posterior region in Platanista. Lines are calculated for
the Ganges dolphin by the method ofleast squares. For other marks see Fig. 4.

the body length and the length of rostrum which are the prominent secondary sexual
characters develop in the female. In Ziphiidae, at least in Berardius bairdi and:(iphius cavirostris, the male is smaller than the female (Omura et al 1955).
Though Platanista resembles with Physeter and Kogia in the anterior situation ofgenital aperture, Platanista may have developed this character independently of theother two species.
It is concluded, from the above discussions, that the pattern of the growth obSci. Rep. Whales Res. Inst.,
No. 24, 1972.

100

KASUYAcm.--~~~~~~~~~~~~~~~~~~~~~~~~,

Gen;tal ape•tu.- to anus ~

30

20
10
100

~~·
... ··--·-- ---. --.p--<a.~---- --- --------· ----··----------·--·
Tail notch to genital aperture

80

.-·

60
40

20

50
Fig. 7.

cm

100

150
200
Body length (cm)

Relative growth of the posterior region in Platanista.

250

For marks see Fig. 6.

Tail notch to tip of dorsal fin

70
50
30

10
50

100

150

200

250

Body length (cm)Fig. 8. Relation between body length and length from tail notch to tip of dolsal fin.
For marks see Fig. 6.
Sci. Rep. Whales Res. Inst.,

No. 24, 1972.

101

GROWTH OF THE GANGES DOLPHINTABLE 9. COEFFICIENT OF THE REGRESSION LINES 3 > OF THE
PROPORTIONAL LENGTH OF THE GANGES DOLPHIN
Upper limit
Measurements

Sex

Length from tail notch to tip of dorsal fin•>to anus1 >to genital apertureI»•>

S?, erS?, er

~

a

"

5?

er

to umbilicus"1 »2 >

5?

er

"

b

Mean

Lower limit

~

~

a

b

a

b

0.357 4.5
0.395 -0.3
0.391 -2.7
0.527 3.5
0.561 -4.2
0.563 1.6

0.335 3.68
0.310 1.06
0.309 4.10
0.479 5.05
0.508 -1.49
0.530 1.93

0.328
1.9
0.266 -0.3
7.7
0.254
0.437
7.1
0.492 -2.4
0.472
6.0

0.058 2.9
0.216 -0.1
0.227 -2.7
0.247 -0.4

0.075 3.22
0.028 0.74
0.187 1.31
0.202 -2.59
0.217 0.23

0.014 -0.3
0.152
2.7
0.177 -1.8
0.254 -11.4

0.179 -0.1

0.166

0.145 -0.7

0.155 -2.2
0.134 -1.6
0.309 -4.6
0.170 -2.8
0.222 -2.6

0.121 -0.85
0.107 -1.51
0.235 -1.47
0.155 -3.77
0.215 -3.50

to anterior insertion of tailS?, erfluke
Length from anus to genital aperture 1 >5?

er
to umbilicusI>

5?

erDistance from anterior insertion of flipper to anterior distal tip 2 >S?, erDistance from axilla to posterior distal tip offlipper
S?, erWidth of flipper 1 »•>S?, erTotal spread of tail flukes 1 »2 >S?, erDistance from tip of to tail flike to tail notch 2 >S?, erto anterior insertion 5?, er(1970), 2 > Include Anderson (1878),
portional and body length shown in cm respectively.

1 > Include Pilleri

3

0.83

0.122
0.098
0.181
0.121
0.160

> Y=aX+b, where Y and X.indicate pro-

100

'Eu
.c

u,c 150

~

>-

"O

0

CD

200

250'--'--'----'---l.---''----'---...L--'-~fip'-'-•r_.__,__.____.'--"--"-'-~-'---'~'---'--'--'--"=---'~
50

100

Distance from tip of rostrum (cm)Fig. 9. Summary of Figs. 4-8, showing change of the relative positions of the externalorgans in the Ganges dolphin. Eye indicates center of eye, ear opening of ear,flipper anterior insertion of flipper, u umbilicus, g.a. genital aperture, d. fin dorsal
fin, anus center of anus, fluke anterior insertion of tail fluke, and t. notch tail notch(left to right). Dotted line is for female and solid line for male.
Sci. R.ep. Whales Res. Inst.,

No. 24, 1972.

-3.4
-2.5
-1.l
-2.3
-0.8

KASUYA102

TABLE 10. DISTANCE BETWEEN THE CENTERS OF GENITAL APERTURE
AND UMBILICUS, MEASURED ALONG THE BODY AXIS AND SHOWN
IN% OF BODY LENGTH
Male

Sex
Species

Platanista g. gangetica
Pontoporia blainvillei(Pilleri 1971)
Stenella attenuata(Nishiwaki et al 1965)
Feresa attenuata(Nishiwaki et al 1965)
Berardius bairdi(Omura et al 1955)
Physeter catodon(Matthews 1938)
Kogia simus(Kasuya et al unpbl.)

Female

N

Range

Mean

N

Range

Mean

12

0.8- 4.1

2.5

6

14.4-22.0

17.1

3

5.1- 7.7

6.0

4

13.0-14.8

13.8

3

17.7-19.2

18.3

4

20.6-25.2

23.4

6

10.5-14.3

12.4

7

12.9-19.4

16.4

20

21.3

5

24.8

60

7.6

8

20.8

7.0

served in Platanista gangetica might have originated from that which had scarcely
showed sexual dimorphism or augmentation of body size. From this hypotheticalprimitive growth pattern, that of recent delphinids and other oceanic toothed whales
may have derived. But, among recent toothed whales, the delphinids seems to haveattained the least modification in the growth pattern. This presumption is compatible with the morphological information on the growth of tooth (see Age determination).
TAXONOMICAL CONSIDERATION OF PLATANISTAIn Figs. 4-8, the proportional measurements of the Indus dolphin cited from Pilleri(1970) are also plotted. Though most of measurements are within the range of individual variation of the Ganges dolphin, the measurements concerning the length oftail show a significant difference between the dolphins from two river systems (Fig.
10, Table 11). Namely, when compared between the dolphins of nearly same bodylength, 118 cm, obtained from the two river systems, the length of tail is 6. 7 cm shorterin the Ganges dolphin than the Indus dolphin. This difference is too large to concider as individual variation or personal deviation of the measurement. There is also
observed a slight difference of the position of the anterior insertion of flipper between
the dolphins from two river systems, which seems to come from the difference of thelength from center of eye to anterior insertion of flipper (Fig. 4). But it can not be
concluded, at present, if the difference is significant or not.
Pilleri (1971) reported the osteological difference observed on the height of nasal
crest as a character to distinguish Platanista gangetica (Lebeck, 1801) and P. indi
Blyth, 1859.
According to Yamashita (1971), the strong Himalayan orogenic movement
started in the middle of Pleistocene, and is still continuing. He also indicated theSci. Rep. Whales Res. Inst.,
No. 24, 1972.

GROWTH OF THE GANGES DOLPHIN

4

103

I
I

1----:---t
,P\:
~2

I

,'

I

'

'

I

I
I

llS

I

:J

I

"CJ

>o

12

"CJ

c

-

16

14

20

18
I

0

I

~-----:-----~
I

Qi 4

I

.0

E
:J
z

,q
I
I

2

0

I

30

32

I

34

I

I

\
'
'

'

'

'

''

'

~--,',,,

36

38

40

Percentage of body length
Fig. 10. Frequency distributions of relative length from eye to anterior insertion offlipper (top), and that from tail notch to anus (bottom) in Platanista, showing themorphological differences between Platanista gangetica gangetica (closed circle andsolid line) and Platanista g. indi (open circle and dotted line). Vertical and horizontal
lines indicate the mean and the ranges of two standard errors in both sides of themean.
TABLE 11. SOME MEASUREMENTS SHOWING THE MORPHOLOGICALDIFFERENCE BETWEEN THE GANGES AND INDUS DOLPHINSSpeciesNo. of samples compared
Range and mean of body length (cm)Length from anus to tail notchrange and mean in cm
range and mean in percentage
Length from eye to flipper
range and mean in cm
range and mean in percentage

Ganges dolphin

Indus dolphinll

13110.0-126.0

117.2

6
108.0-126.0

118.3

33.5- 43.0
29.6- 36.8

37.6
32.l

38.0- 46.0
35.2- 40.7

44.3
37.4

15.0- 21.0
12.8- 18.6

18.3
15.7

16.0- 18.5
13.0- 15. 7

16.9
14.3

ll Pilleri, 1970

possibility that the upper streams of some river had shifted, during this period, to havea connection with another river. This kind of exchange of the drainage area may
have occurred between the Indus and the Ganges-Brahmaputra, which will haveoffered the chance for the Platanista to expand its habitat to another river, or to exSci. Rep. Whales Res. Inst.,

No. 24, 1972.

104

KASUYAchange the animal between connected two rivers. Anyway there will be no doubtthat Platanista in the two river systems had originated from the same origin, andgained some morphological differences as the result of the separate evolution.
In some species of Mysticeti (Nishiwaki and Kasuya 1970, Omura 1957, Omura
et al 1970), the characters of nasal or tail region seems to be the character where thedifferentiation occurs rapidly. Probably same presumption will be possible on
Platanista. And, in my opinion, the evidence is still insufficient to consider Platanista
gangetica and P. indi as two distinct species. The best way, at present, will be to deal
them as two subspecies, or Platanista gangetica gangetica and Platanista gangetica indi.
SUMMARY
By the consideration of the growth of the Ganges dolphin based on the 22 individuals
obtained in East Pakistan, the following results were obtained.
1. As the age characteristics, the growth layers in dentine is the best among
the three characteristics compared in this study.
2. The opaque layers in dentine is suggested to be formed in summer, and thetranslucent in winter.
3. One of the peak of parturition season is in December and January, and theother, probably in early summer.
4. The calf seems to be born at about 70 cm in body length, and attain the
body length of 116 cm in one year, and 123 cm in 1.5 years.
5. The calf probably start feeding at 1 or 2 month after birth, and weaning isaccomplished within one year.
6. The sexual maturity is supposed to be attained at the age of 10 or slightly
less, and the physical maturity, in the males, at the age more than 20 years.
7. The body weight of the adult female is slightly smaller than that of the maleof the same body length.
8. Sexual dimorphism is observed in the body length, length of rostrum,
positions of genital aperture and umbilicus, and perhaps in the position of flipper.
9. The growth pattern of Platanista seems to have originated from that probably had observed in primitive delphinids.
10. There is a clear difference of the length of tail between the Ganges dolphin
and the Indus dolphin. And it is proposed to deal them as separate subspecies.
ACKNOWLEDGEMENTGreatest thanks are due to Prof. A. K. M. Aminul Haque of the Bangladesh
Agricultural University, without his cooperation present study would not have beenaccomplished. The Kamogawa Sea World and all the members of the Cetacean
Research Expedition are also acknowledged for their help offered in East Pakistan
and in Japan.

Sci. Rep. Whales Res. Inst.,.No. 24, 1972.

GROWTH OF THE GANGES DOLPHINAPPENDIX I.
Specimen no.
Sex
From tip of upper jaw to:
1. tail notch (total length)
2. anterior end of nasal slit
3. angle of gape
4. center of eye
5. ear
6. anterior insertion of flipper
From tail notch to:
7. tip of dorsal fin
8. anterior insertion of tail fluke
9. center of anus
10. center of genital aperture
11. center of umbilicus
From angle of gape to:
12. center of eye
13. ear
From ear to:
14. eyeFlipper:
15. anterior insertion to anterior distal tip, straight
16. anterior insertion to anterior distal tip, along
curvature
17. axilla to posterior distal tip
18. greatest width
19. width at baseDorsal fin:
20. length of base
21. height
Tail fluke:
22. tip to tip (total spread)
23. tip to notch
24. tip to anterior insertion
Nasal slit:
25. length

Sci. Rep. Whales Res. Inst.,

EXTERNAL MEASUREMENTS

14

21

5

11

15

16

18

<;!

<;!

<;!

<;!

<;!

<;!

<;!

27.0 76.0 110.0 113.0 118.0 120.5 126.0
6.0 14.5 18.0 25.0 21.0 26.2 23.0
3.5 13.5 19.5 21.0 23.5 26.2 24.0
4.2 13.5 18.5 21.0 22.5 26.6 23.0
6.5 19.0 26.0 28.2 30.0 33.0 31.5
9.5 26.5 37.5 42.0 40.0 44.0 42.0
11.0 29.0 39.0 39.0 43.0 45.9 45.0
9.0 12.0 12.0 10.5 13.6 11.5
7.5 25.5 35.0 34.5 37.0 39.2 39.0
40.0 41.7 41.0
27.0 37.5
10.9 39.0 56.0 55.0 56.0 59.0 62.0
2.3
6.5

3.2
8.3

5.5

7.8

3.2

13.5

18.5

3.0
9.5
7.5

8.0

9.0

18.0

19.1

18.0

2.0
2.0

14.5 20.5 20.0 20.0
9.5 13.0 12.5 13.0
6.5 11.0 11.5 11.0
4.0
2.5

21.0
13.5
12.6

19.5
13.5
11.0
4.0

3.3
0.4

9.0
1.5

12.0
2.0

7.0
2.0

25.5
3.1

10.0
1.3

3.8
1.8
3.5

15.0 24.0
8.0 12.5
14.0 18.5

27.0
15.0

26.5 24.3 25.0
14.0 12.4 15.0
19.0 19.0 22.5

1.1

2.5

4.0

4.0

In nos. 1 to 11, length was measured in parallel with body axis.

No. 24, 1972.

105

4.5

18.0

2.5

4.5

5.8

106

KASUYAOF THE GANGES POLPHIN (cm).

17

2

1

<?

6

6

7
6

3

13

12

6

9

8

19

22

4

20

10

6

6

6

6

6

6

6

6

6

6

6

127.0 100.5 105.0 113.0 115.0 115.0 115.5 117.0 117.5 121.5 122.0 128.0 171.5 199.0 200.0
24.0 (16.3) 19.5 21.5 (17.0) 19.0 20.0 22.0 23.5 24.0 19.5 25.0 34.0 33.0
24.5 17.0 18.5 23.0 20.0 21.3 19.5 21.5 23.0 23.5 21.0 28.5 31.6 37.5 36.0
23.5 16.5 18.2 21.5 18.0 20.0 19.0 21.0 22.5 22.0 20.0 26.0 29.2 35.0 35.0
47.5 48.0
33.5
27.8 27.0 28.0 30.0 30.0 29.0 34.0
29.0
45.0 31.0 35.0 40.5 35.0 38.5 37.5 36.0 40.5 41.0 39.5 47.0 54.6 69.0 76.0
47.0 37.0 39.0 41.0 44.5 42.0
11.0 11.0 13.0 11.0 12.8 12.0
43.0 33.0 33.0 33.5 39.5 35.5
45.5 51.0 54.5 58.0 63.0 59.0
67.0 54.0 56.0 61.0 65.5 63.0
4.2
9.0

42.5 46.5 41.0 44.0 46.0
12.0 12.5 12.0 13.0 11.5
36.5 43.0 39.5 38.0 38.5
59.0 65.0 60.0 63.5 62.0
61.5 67.5 61.5 64.5 67.0

47.0 64.8 68.0 72.0
11.5 16.5 18.5 18.5
39.0 55.3 61.0 60.0
65.0
94.0 102.0
70.0
100.0 109.0

3.4
9.4

3.5
9.5

2. 7
9.5

3.0
9.3

3.5
9.5

3.0
9.5

3.5
9.0

4.5
14.0

6.0
16.0

9.0

7.5

8.0

8.0

8.0

8.8

8. 7

9.0

8.0

8.8

9.5

8.0

13.5

14.0

20.5

15.5

17.5

19.0

17.0

19.0

19.0

19.0

18.5

18.0

17.0 21.0

35.5

29.0

23.0
14.0
15.0

17.5
11.5
8.0
3.5

19.0 21.0
12.0 13.0
10.0 9.5
4.0
3.5

16.0
2.5

19.5 21.3 21.0 21.5
13.0 13.2 13.5 14.0
8.5 11.5 11.5 9.0
3.0
4.0
3.0
8.0
2.8

21.0
4.5

1.5

19.0
2.0

20.5 20.0
12.5 13.0
11.5 12.5
4.0
4.0

39.5 33.0
19.5 22.5
11.5 15.5 24.4 23.0 21.0
11.0 14.0 17.8 25.0 22.5
4.5
5.0 5.7
7.0
7.0

17.0
3.0

11.0
1.5

18.0
3.0

12.5
3.1

36.0
5.5

28.0 23.0 22.5 26.5
16.0 13.0 11.0 15.5
23.0
22.5

26.5
14.5

26.5 25.0 28.5 27.0 28.5 29.0 29.0
15.3 13.5 15.0 15.0
16.0 15.5
22.5 20.5 22.0 21.5 22.5 21.0 24.0

38.7

57.0 42.5
30.0 23.0
38.5 33.0

4.5

3.3

2.8

5.6

8.0

4.3

4.3

4.3

3.5

4.8

4.8

3.5

5.0

4.0

6.0

Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

GROWTH OF THE GANGES DOLPHIN107

REFERENCES
ANDERSON, J., 1878. Anatomical and ,Zoological researches comprising an account of the ,Zoological results of the two
expeditions to Westerm Yunnan in 1868 and 1875 and a monograph of the two cetacean genera, Platanista andOrcella, vol. I. Bernard Quaritch, London, 550 pp.
KASUYA, T., 1972. Crowth and reproduction of Stenella caeruleoalba based on the age determination bymeans of dentinal growth layers. Sci. Rep. Whales Res. Inst., 24: 57-79.
KASUYA, T., and A. K. M.A. HAQ.DE, 1972. Some informations on the distribution and seasonal movementof the Ganges dolphin.Sci. Rep. Whales Res. Inst., 24: 109-115.
MATTHEWS, H., 1938. The sperm whale, Physeter catodon. Discovery Rep., 17: 93-168.
NrnmwAKI, M., T. HIBIYA, and S. 0HSUMI (KIMURA), 1958. Age study of sperm whale based on reading of
tooth laminations. Sci. Rep. Whales Res. Inst., 13: 135-153.
NrnmwAKI, M., S. 0HSUMI, and Y. MAEDA, 1963. Change of form in the sperm whale accompanied withgrowth. Sci.Rep. WhalesRes.Inst., 17: 1-14.
NrsmwAKI, M. and T. KASUYA, 1970. Recent record ofgray whale in the adjacent waters of Japan and aconsideration on its migration. Sci. Rep. Whales Res. Inst., 22: 29-37.
0HSUMI, S. 1966. Allomorphosis between body length at sexual maturity and body length at birth in the
cetacea. J. Mamm. Soc. Japan, 3(1): 3-7.
0HSUMI, S., T. KAsUYA, and M. NISHIWAKI, 1963. The accumulation rate of dentinal growth layers in the
maxillary tooth of the sperm whale. Sci. Rep. Whales Res. Inst., 17: 15-35.
Ol>IURA, H., 1959. Bryde's whales from the coast ofJapan. Sci. Rep. Whales Res. Inst., 14: 1-33.
OMURA, H., K. FUJINO, and S. KIMURA, 1955. Beaked whale Berardius bairdi of Japan, with notes on ,Ziphiuscavirostris. Sci. Rep. Whales Res. Inst., 10: 89-132.
OMURA, H., T. lcHIHARA, and T. KASUYA, 1970. Osteology ofpigmy blue whale with additional information
on external and other characteristics. Sci. Rep. Whales Res. Inst., 22: 1-27.
PrLLERI, G., 1970. Observation on the behaviour of Platanistagangetica in the Indus and Brahmaputra Rivers.
Investigations on Cetacea, 2 : 27-60.
Pilleri, G., 1971. On the La Plata dolphin, Pontoporia blainvillei off the Uruguayan coast. Investigations on
Cetacea, 3(1) : 59-68.
PrLLERI, G., and GrnR, M., 1969. Zur Anatomic and Pathologie von Inia geoffrensis de Blainville 1817
(Cetacea, Susuidae) aus dem Beni, Bolivien. Investigations on Cetacea, 1 : 94-108.
PrLLERI, G., and GrnR, M., 1971. Differences observed in the skull of Platanista indi and gangetica. Investigations on Cetacea, 3(1): 13-21.
SERGEANT, D. E., 1962. The biology of the pilot whale or pothead whale Globicephala melaena (Trail) m
Newfoundland waters. Bull. Fish. Res. Board of Canada, 132: 1-84.
YAMASHITA, N., 1971. The history of Himalayas. Science (inJapan), 41(4): 221-230. (inJapanese).

Sci. Rep. Whales Res. Inst.,

No. 24, 1972.

108

KASUYA

EXPLANATION OF PLATESPLATE I
Ground thin section of the teeth of Ganges dolphin, translucent layers are shown black andopaque layers white.
Fig. 1. Specimen no. 20, male, body length 199 cm, number of growth layers 28.
Fig. 2. Specimen no. 4, male, body length 171.5 cm, number of growth layers 10.
Fig. 3. Specimen no. 18, female, body length 126.0 cm, number of growth layers 1 3/4.
PLATE II
Ganges dolphin, no. 21, female, body length 67.4 cm. Photographed at the time of capture. Anterior most one or two pairs of teeth started to erupt, and hairs are observed on theboth jaws.
PLATE III
Ganges dolphin, no. 7, male, body length 113 cm. In fresh condition the colouration 1s
pale brown with a tinge of gray. The colour of throat and chest region is paler.

Sci. Rep. Whales Res. Inst.,
No. 24, 1972.

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