BIOTROPIA Vol. 28 No. 1,2021: 1 - 10 DOI: 10.1 1598/btb.2021.28.1.623 

REPRODUCTIVE BIOLOGY OF FRESHWATER CLAM POKEA 
(Ba tissa violacea VAR. celebensis, V O N  MARTEN 1897) (Bivalvia: 

Corbiculidae) I N  POHARA RIVER, KENDARI, SOUTHEAST 
SULAWESI PROVINCE, INDONESIA 

BAHTIARl, LA ANADI1, WA NURGAYAHl, M HAMZAH* AND UDHI E. HERNAWANZ 

'Faczllty ofFideries and Marine Science, Huluoleo University, Jalan HEA Mokodompit No. 1 Maluka Andzlonohzl, 
Kendari 93232, Indonesia 

2Reseurch Centerfor Oceanogr@h_y, Indonesidn Institnte ofSciences, Jalun Pan' Putih I ,  Ancol Timur, Jakarta 14430, Indonesia 

Received 15 February 2016/Accepted 23 December 2019 

ABSTRACT 

The freshwater clam, locally known as Pokea, (Butissa violaceu var celebensis, von Martens 1897; Bivalvia: 
Corbulidae) is a popular and widely consumed food in Icendari, Southeast Sulawesi. Despite its popularity, basic 
information required for conservation management, such as reproductive biology, is lacking. Hence, this study 
aims to examine the reproductive biology of the clam obtained from Pohara River, Icendari, Southeast Sulawesi 
Province, Indonesia. Pokea samples were collected monthly from February 2012 to January 2013. Its 
reproductive biology, including sex ratio, stage of gonadal maturity, gonadosomatic index (GSI), fecundity, and 
size of the first mature gonad from each sample were recorded. Data were analyzed using chi-square test 
and linear regression in the package Sigma Plot v.6.O. Pokea population in Pohara River was male-biased. The 
population spawns throughout the year and the peak spawning season was in August-September. Mature gonads 
were found at small shell size (indicating early sexual maturity). This gonadal development in Pokea that might 
have been influenced by food availability, is a very relevant baseline information for the conservation of Pokea 
population in the Pohara River. 

Keywords: clams, freshwater, gonadal maturity, spawning 

INTRODUCTION 

The freshwater clam, locally known as Pokea, 
( B a t k  uiolacea var celebensis, von Martens 1897, 
Bivalvia: Corbulidae) is a popular and widely 
consumed food in Icendari, Southeast Sulawesi 
(Fig. 1). Geograplucally, the genus Batissa is 
widely distributed in the western and southern 
Pacific (from Malaysia, Philippines, Papua New 
Guinea, Western Australia to Fiji) (Dudgeon & 
Morton 1989). B. uiolacea was known to be 
distributed in Southeast Asia and Northern 
Australia (Sastrapradja 1977). In Indonesia, this 
species occurs in some of the big islands, 
incluchng Sumatra (Putri 2005), Java 

*Corresponding author, email: udhiehernawan@gmail.com 

(Sastrapradja 1977), Papua (Djajasasmita 1977) 
and Sulawesi (I<usnoto 1953). In Southeast 
Sulawesi, the clams are found in some of the big 
rivers in the Southeast Peninsular, such as 
Pohara River, Lasolo River, Roraya River and 
Laeya Ever (Bahtiar 2005). Ecologically, this 
species occupies the substrate surface or lives 
beneath the substrate in the river estuary 
(Sastrapradja 1977; Djajasasmita 1977; Bahtiar 
2007a). Pokea can be found in a variety of 
sediment types, from gravel to clay (Bahtiar 
2007b; Bahtiar et al. 2008). This clam species 
lives in small and big colonies (Bahtiar 2007a). 
These clams were believed to have different 
reproductive characteristics from other species 
of freshwater bivalves. This is because 
individuals of the clams are unisexual, while 
other species are mostly hermaphrodite. 



BIOTROPIA Vol. 28 No. 1,2021 

Figure 1 The freshwater clam Pokea ( B a t h a  violacea var cehbensis) 
Notes: A: width; B: length. 

Very likely due to a combination of 
uncontrolled harvesting and sand mining in its 
habitat, the Pokea populations in Pohara River 
have been declining. This is manifested by the 
declining trend of both the number and size of 
the sampled pokea. In addition, localized 
extinction has been reported in the mining areas. 
This situation calls for some form of 
conservation management intervention of this 
species (Bahtiar e t  al. 2012). Despite its high 
demand for consumption, coupled with its 
declining populations, some basic information 
required for effective conservation management, 
such as reproductive biology, is lacking (Bahtiar 
2012). Accurate information on the reproductive 
biology of this species is critically relevant for 
several conservation practices, particularly in 
determining the harvesting season and minimum 
clam size for sustainable harvesting (Cantillaneza 
e t  al. 2005). Hence, this research aims to examine 
the reproductive biology of the Pokea clam in 
Pohara River, Kendari, Southeast Sulawesi. 

MATERIAL AND METHODS 

Sample and Data Collection 

122023'556" E), from February 2012 to January 
2013 (Fig. 2). During the first week of each 
month, a total of 120 individual clams were 
collected, then separated based on the gender. 
Male individuals have milky white colored 
gonad, while female ones have brown colored 
gonad. The recorded parameters for 
reproductive biology, included sex ratio, 
fecundity, stage of gonadal maturity, gonado 
somatic index, and size of the first mature gonad 
from each samples. 

Gonadal development was divided into 5 
levels: inactive (stage I), early development 
(stage 11), final development (stage 111), mature 
(stage IV), spawning/post-spawning (stage V). 
This gonadal development was examined based 
on the gonad morphology and histology (Bahtiar 
2012). The gonado somatic index (GSI) was 
measured based on Illanes e t  al. (1985) and 
Wolff (1987) methods. Fecundity was assessed 
based on gravirnetric method, using egg weight, 
total gonad weight, and body weight (Eiffendi 
2002). Size of the first mature gonad was 
screened from all class sizes (Arocha & Barios 
2009). The phytoplankton abundance was also 
recorded at the sampling sites. All laboratory 
works were conducted at the Faculty of 

Pokea samples were collected monthly from Fisheries, Haluoleo University, Icendari, 
the estuary of Pohara River (03"58'551m S and Southeast Sulawesi Province, Indonesia. 



Reproductive biology of freshmter dam Pokea in P o h m  River - Bahtiar d al. 

'4 0 160 3201(m - 
C 

- v - -  - 1 S E A  
0 345mwm 

d MARS DI-T 

I 
I N E  G U L  

i- 

. . I 
WEST 

UYrroeIOl(mET 

R O R  I E A  

. 
0 66 1M Km 

tmm! ,A&=- s '- ns%w€ 1-RE - 
Figure 2 Map of the sampling sites at Pohara River, Kendari, Southeast Sulawesi Province 

Data Analysis 

The significant difference of the sex ratio was 
determined using the Chi-square (X? test where: 
(Mzighani 2005), using the following formula: = fecundity number 

where: 

" (Oi - ei)' x2 = C 
i=l O i  

n = number of eggs from sampled gonads 
G = total gonad weight 
g = weight of the sampled gonads 

Oi = The number of males and females The relationship between fecundity and the 
observed at i 

shell width was analyzed using regression 
ei = The expected number of males and analysis (Steel & Torrie 1981). The probability 

females at i 
of mature gonad was calculated using nonlinear 
regression functions with a logarithmic curve 

Gonado somatic index (GSI) was calculated 
(Arocha & Barios 2009), using the following 

using the formula described by Sastry (1979): formula: 

Bg GSI = - ~ 1 0 0 %  
Bt 

where: 
GSI = gonado somatic index 
Bg = gonad weight (g) 
Bt = body weight includmg gonad (g) 

Pokea's fecundity was calculated based on the 
gravimetric method (Effendi 2002), using the 
following formula: 

where: 
Y = probabihty of mature gonad (Yo) 
e = exponential function 
a = intercept 
b = slope 
x = width at i (cm) 



BIOTROPIA Vol. 28 No. 1,2021 

The relationshp between the GSI and Gonadal development represents the 
phytoplankton abundance was analyzed using reproductive processes that occur until the 
the Pearson correlation. All statistical analyses spawning event. The processes were divided 
were done using Sigma Plot v.6.O. into five stages, from inactive phase to the 

spawning phase. The parallel gonadal stages of 
both male and female Pokea observed in this 

RESULTS A N D  DISCUSSION study confirmed the studes of Bahtiar (2012). 

Sex Ratio 

The number of male individual clams was 
higher than that of the female individuals at each 
sampling month, at an average male/female 
ratio of 65/35 (Table 1). The sex ratio was 
significantly male biased, indicated by the Chi- 
square test value = 0.0003). This male-biased 
sex ratio conforms with previous studies by 
Bahtiar (2005) and Bahtiar (2012). However, sex 
ratio in bivalve population is not always male- 
biased but varies with different species. For 
example, the clam Gam' elongata population 
exhbited a slightly female-biased sex ratio 
(Nabuap & Campos 2006). The male-biased sex 
ratio might be the consequence of the fact that 
(i) Pokea reproduces by external ferohzation, 
and (ii) males of Pokea are generally smaller in 
size than females. In external fertilization, the 
sperms are subjected to greater mortality in the 
aquatic environment. Therefore, to increase the 
probability of a successful fertilization, the 
number of male individuals should be higher 
than that of female indviduals (Bahtiar 2012). 

Table 1 Sex ratio of the freshwater clam Poliea 

Furthermore, the peak periods of spawning 
events were also similar. Partial spawning was 
also observed based on the changes in the egg 
dameter. Egg diameters at gonadal stage IV 
consisted of two size groups, with median values 
of 21.60 pm and 159.16 pm (Bahtiar 2012). At 
the post-spawning stage Or), three size groups 
were reported, with median value of 22.80 pm, 
172.06 pm and 262.82 pm (Fig. 4). T h ~ s  
condition implied that the eggs reached maturity 
at different periods, indicating that the Pokea 
spawns throughout the year. Therefore, Pokea 
can be classified as a partial/multiple spawner, 
although it has a peak period of spawning. 
Partial/multiple spawner is common in bivalves; 
for example the clam V e n w  veracosa spawns all- 
year long, however the spawning event peaks in 
August. Some populations spawn in December 
Firado etal. 2003), or the clam Donax tmnc~lzls 
shows two peaks of spawning periods (March 
and August) with gametogenesis cycle starts in 
late November and finishes by the end of 
August (Gaspar e t  al. 1999). 

Month Male (%) Female (O/O) 

March 2012 

April 201 2 

May 2012 

June 2012 

July 2012 

August 2012 

September 2012 

October 2012 

November 2012 

December 2012 

January 201 3 

F e b m a ~  201 3 

Total 65.0591 34.9409 



Reproductive biology of freshwater clam Pokea in Pohara River - Bahtiar e t  al. 

Male 

loo 1 

C, 
c 

E 
a 20 0 
0 - 
? -  
a g 
m u  Female 
- 
-0 

0 

40 

20 " i  o 2012 20 13 
M a r  Apr May Jun Jul A u g  Sep Oct Nov Dec Jan Feb 

Figure 3 Stages of gonadal development in male and female Pokea 
Notes: Stage I (inactive); early Stage I1 (development); 

Stage I11 (final development); Stage IV (mature); 
and Stage V (spawning/post-spawning). 

I Gonad stage 1 V Gonad stage V 

Gonadal 
stage 

Egg diameter ( l m )  Egg diameter (pm) 

Figure 4 Bhattacharya analysis on the distribution of egg diameter on gonadal stage IV and V (modified from 
Bahtiar 2012) 

Gonado Somatic Index (GSI) from 1.46 to 15.69, and peaked in July. After the 

Both male and female Pokea showed similar peak event in July, the GS1 value 

temporal patterns of GSI. Averaged GSI ranged declined in August-September 2012 (Fig. 5). 



BIOTROPIA Vol. 28 No. 1,2021 

Female 

Male 

0 I I I I I I I I I I I I I 
2012 20 13 
Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb 

Observation month 

Figure 5 Mean GSI of male and female h k e a  in each observation month 

GSI indicates annual reproductive cycle and 
it links with the stages of gonadal maturity. 
Therefore, a concordance of temporal pattern 
existed between GSI and gonadal stages, in 
whch GSI peaked in July, followed by the peak 
of spawning event in August-September. Bahtiar 
(2012) also reported a similar pattern. 
Reproductive cycles in bivalves varies with 
different species. For example, Corbicula 
australis spawns at the end of September and 
October (Bryne 2000), while Corbicula Puminea 
spawns twice a year in early May or June and late 
September (Mouthon 2001). This intraspecific 
variation in the reproductive cycle is probably 
related with different geographical locations. 
However, this is not conclusive as evidences or 
studies on the reproductive biology of Pokea are 
still lacking. 

Gonadal maturity is determined based on egg 
diameter changes in each month, as egg size 
represents reproductive growth in the gonad 
(Haggertyet al 2005). When the GSI values 
were compared, changes in egg diameter showed 
a similar temporal pattern. This is because the 
GSI value is determined by egg size (Bahtiar 
2012) (Fig. 6). A similar pattern was also 
observed in the species Megalonaias nervosa 
showing the number and size of oosit increased 
at the end of June (mature gonad) unul the end 

of September (spawning), then decreased in 
early October (inactive phase) (Haggerty et al 
2005). 

Fecundity 

The relationship between fecundity (I?) with 
the median class of shell width (L) was 
determined from a simple regression equation, 
F = 36815"L-81706 with a determination 
coefficient (R) = 0.97. An individual with a 
minimal shell width of 2.97 cm contained a total 
of 4652 eggs, while another one with a width of 
5.93 cm contained 130,465 eggs (Fig. 7). 
Numbers of eggs foundin this study were 
relatively smaller compared with the findings of 
Bahtiar (2012) ranging from 4,950 to 1,007,384. 
The small number of eggs observed in this study 
might be a consequence of the environmental 
disturbances resulted from the sand mining 
activities. The dsturbances might have triggered 
the early maturity of the clams resulting in the 
decreased number of eggs. Compared with other 
species, the egg number recorded in t h s  study 
was much lower. For example, the unionid 
mussels (Unionidae) contained 200,000 to 
17,000,000 eggs (Vaughn 2005) and the macker 
mussel Actinonaias hgamentina contained 80,616 
to 1,561,224 eggs (Moles & Layzer 2008). 





BIOTROPIA Vol. 28 No. 1,2021 

Shell width (cm) 

Figure 7 Linear relationship between fecundity and shell width in Pokea 

o Male 
4 Female 

0 2 4 6 8 

Shell width (cm) 

Figure 8 Size of the first mature gonad in male and female Pokea 

Relationship between the Reproductive the bivalve reproductive performance. The 
Parameters and Environmental Factors important role of food availability in triggering 

Simple h e  plots showed a concordance 
between the reproductive performance of Pokea 
(GSI) and environmental conditions 
(phytoplankton abundance). This pattern was 
further examined in a simple linear regression 
showing that the relationship has a coefficient of 
determination, R2 = 69.05% (Fig. 9). As Pokea 
feeds on phytoplankton, the increase of 
phytoplankton abundance in July might be 
related with gonadal maturity in Pokea, as it 
reached a spawning peak in August-September. 
Hence, environmental condition has influenced 

sexual maturity has been well documented, 
particularly in bivalve farming. The increased 
GSI in A m e l t e n  iradians was stimulated by an 
external factor that increased availability of food 
in terms of organic matter (Gosling 2002). The 
increase of GSI in Gam' elongata occurred 
following the increased of food supply, again in 
terms of organic matter (Nabuab & Campos 
2006). Other environmental factors, such as pH, 
temperature, organic matter, and seston, might 
also be important Pahtiar 2012). 



Reproductive biology of freshwater clam Pokea in Pohara River - Bahtiar et al. 

f + Phytoplankton abundance I 

Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb 

Observation month 

Figure 9 Relationship between GSI and phytoplankton abundance 

CONCLUSION (Tetraptzlw albidus) from the Western Central 
Atlantic. Aust J Mar Freshwater Res 43:393-402. 

The Pokea (Batissa violacea var celebensis) Bahtiar. 2005. Icajian populasi Pokea (Batissa violacea var. 
population in Pohara &ver was male-biased. celebensis, von Martens, 1897), 1897 di Sungai 

The population spawned throughout the year Pohara, Icendari, Sulawesi Tenggara. vhesis]. 
Bogor (ID): Institut Pertanian Bogor. 

and the peak spawning season was in August- 
september. Mature gonad was found at small Bahtiar. 2007a. IConservasi populasi Pokea (Batissa violacea 

var. celebensis von Martens, 1897), di Sungai Pohara, 
shell size (indicating early sexual maturity). Food Icendari, Sulawesi Tenggara. Laporan Hibah 
availability might have influenced the gonadal Bersaing. Jakarta (ID): DP2M-Dikti. 
development in Pokea. T h s  is a very relevant 
baseline information for the conservation 
management of Pokea population in the Pohara 
River. 

ACKNOWLEDGMENT 

The authors would like to thank all the field 
assistants during the sampling period and the 
Dean of the Faculty of Fisheries and Marine 
Sciences, Haluoleo University, I<endari, 
Southeast Sulawesi, Indonesia for the support 
and suggestions for the completion of this study. 

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