Length-weight relationship and GSI of hilsa, Tenualosa ilisha (hamilton, 1822) fishes in Meghna river, Bangladesh

Abstract

The hilsa shad, Tenualosa ilisha (Hamilton, 1822) is an important anadromous clupeid fish species from the western division of the Indo-Pacific region. The present study dealt with the length weight relationship and GSI of hilsa shad using monthly samples over a calendar year from January to December 2013 from the river Meghna flowing through Chandpur district in Bangladesh. A total of 517 specimens (171 male and 346 female) of hilsa were collected. The reproductive characteristic of T. ilisha showed M: F=1:2 sex ratio which indicating predominance of females over the males. The parameter values of the equation W=aL b describing the relationships between total body weight (BW) and total length (TL) for male and female varied monthly. The generalized length-weight relationship was fitted with the pooled data of all monthly samples for male and female separately. The generalized length-weight relationship was fitted with the pooled data of all monthly samples for male and female separately which were BW = 0.01TL 3.040 (R 2 =0.902) and BW = 0.008TL 3.078 (R 2 =0.822) respectively. The results revealed that all length-weight relationships were highly correlated (r>0.891). Gonadosomatic index (GSI) was found highest in October and values ranged 1.6-24 in female in case of male values ranged from 0.67-1.5 from and the lowest in December. The present data on male, female and combined fish functional length-weight relationships are important for fish stock assessment. These results will be helpful for fishery managers to impose adequate regulations for sustainable fishery management in Bangladesh.

Full text

International Journal of Natural and Social Sciences 2 (2015) 82-88 ISSN: 2313-4461
How to cite this article: Flura, M Zaher, BMS Rahman, MA Rahman, MA Alam and MMH Pramanik (2015).
Length-weight relationship and GSI of hilsa, Tenualosa ilisha (hamilton, 1822) fishes in Meghna river, Bangladesh.
International Journal of Natural and Social Sciences, 2(3): 82-88.
Length-weight relationship and GSI of hilsa, Tenualosa ilisha (hamilton, 1822)
fishes in Meghna river, Bangladesh
Flura1, Muhammad Zaher2, B.M. Shahinur Rahman3, Md. Anisur Rahman1, Mohammad Ashraful
Alam1, Md. Mehedi Hasan Pramanik1
1Bangladesh Fisheries Research Institute, Riverine Station, Chandpur-3602, Bangladesh
2Bangladesh Fisheries Research Institute, Mymensingh 2201, Bangladesh
3Bangladesh Fisheries Research Institute, Shrimp Research Station, Bagerhat-9300, Bangladesh
ABSTRACT
The hilsa shad, Tenualosa ilisha (Hamilton, 1822) is an important anadromous clupeid fish species from the
western division of the Indo-Pacific region. The present study dealt with the length weight relationship and
GSI of hilsa shad using monthly samples over a calendar year from January to December 2013 from the
river Meghna flowing through Chandpur district in Bangladesh. A total of 517 specimens (171 male and
346 female) of hilsa were collected. The reproductive characteristic of T. ilisha showed M: F=1:2 sex ratio
which indicating predominance of females over the males. The parameter values of the equation W=aLb
describing the relationships between total body weight (BW) and total length (TL) for male and female
varied monthly. The generalized length-weight relationship was fitted with the pooled data of all monthly
samples for male and female separately. The generalized length-weight relationship was fitted with the
pooled data of all monthly samples for male and female separately which were BW = 0.01TL3.040
(R2=0.902) and BW = 0.008TL3.078 (R2=0.822) respectively. The results revealed that all length-weight
relationships were highly correlated (r>0.891). Gonadosomatic index (GSI) was found highest in October
and values ranged 1.6 -24 in female in case of male values ranged from 0.67-1.5 from and the lowest in
December. The present data on male, female and combined fish functional length-weight relationships are
important for fish stock assessment. These results will be helpful for fishery managers to impose adequate
regulations for sustainable fishery management in Bangladesh.
Key words: Hilsa shad, Tenualosa ilisha, length-weight, GSI, Meghna river, Bangladesh.
*Corresponding author.
E-mail address: flura_bfri@yahoo.com (Flura) @2015 Int. J. Nat. Soc. Sci. all right reserved.
INTRODUCTION
The country’s most important aquatic resource is
the ilish (hilsa shad). It is the largest and single
most valuable fishery in Bangladesh and an
important fishery in India, Myanmar, Malaysia,
Vietnam, and Iran, Kuwait and Iraq in the Middle
East (FAO, 1974). Average hilsa production in
Bangladesh is about 351 thousand metric ton
(MT). Hilsa contributes 1.0% to the GDP (DoF
2014). It is the national fish of Bangladesh and the
largest single species fishery contributing 75% of
total catch in this region (Raja 1985) that accounts
nearly half of the total marine catch and about 12-
13% of total fish production of the country
(Haldar, 2008). At present about 0.46 million
people directly or indirectly are engaged in hilsa
and jatka fishing.
A considerable amount of hilsa is exported from
Bangladesh and the foreign currency is earned
equivalent to about Tk.1500 million. Hilsa is
mainly exported to West Bengal, India and some
other countries in the Far East and Middle-East,

Flura et al., International Journal of Natural and Social Sciences 2 (2015) 82-88 83
International Journal of Natural and Social Sciences, ISSN: 2313-4461; www.ijnss.org
European Union, America and Australia. Its
marine distribution extends from Iran and Iraq in
the Persian Gulf to the west coast of India in the
Arabian Sea and the Bay of Bengal (Ahmed et al.,
2008). Hilsa shad supports a commercial fishery
and in the early 1970s composed more than 95 %
of the total commercial catch in Bangladesh (Coad
et al., 2003). The fishery provides livelihood to
about 2.5 million people (about 2% of the total
population) directly or indirectly (Mazid et al.,
2007). T. ilisha is a very important food fish in
south- west of Iran. The Hilsa shad is an
anadromous species, but two other ecotypes - a
fluvial potamodromous type and a marine type
have been recognized. The potamodromous stocks
appear to remain in the middle reaches of the
rivers throughout the year and breed there in. The
anadromous stocks, whose normal habitat is the
lower region of the estuaries and the foreshore
areas, ascend the rivers during the breeding season
and return to the original habitat after spawning
(Panhwar et al., 2011). Therefore, the exact stocks
are still in dispute. As for other tropical fish,
ageing of hilsa is problematic, because of the
absence of annual rings on scales (Rahman and
Cowx, 2006). However, length-weight relationship
is an important tool in fish biology, physiology,
ecology, fisheries assessment and fish
conservation. In t he pre sent stu dy, length-
weight relationships of T. ilisha were estimated
to know the status of the hilsa fishery in
Bangladesh, which could be helpful for
management of the fishery.
MATERIALS AND METHODS
Fish samples were collected month wise during
January to December 2013 from the south part of
Meghna river. A total of 517 specimens (171 male
and 346 female) of hilsa ranging size from 20.9-
47.8 cm in total length (TL) and 200-1260 g in
total body weight (BW) were collected randomly
for the analysis. The collection details of hilsa
used for this study are given in Table 1. The total
length was measured as the distance from snout to
the tip of the caudal fin and body weight was taken
with an electric digital balance for each fish after
the specimens were dried on blotting paper.
The relationship between the total length (TL) and
total body weight (BW) of fish was estimated by
using the equation:
BW= aTLb
Where,
BW=Body weight of fish in (g)
TL=Total length of fish in (cm)
a=Constant (intercept)
b=an exponent indicating isometric growth
when equal to 3.
The reproductive cycle of a species for the year
round fortnightly or monthly intervals can be
determined by gonadosomatic index (GSI). It is a
very useful method to indicate the spawning
season of the species at the field level. GSI
assumes that a gonad increases in size with
increasing development comparing with the mass
of the gonad (GW) to the total mass of the animal
(BW). The gonadosomatic index of each fish was
calculated. The gonadosomatic index of each fish
specimen in the study was calculated as GSI (%) =
Gonad weight (g) × 100 / Body weight (g). The
spawning seasons determined based on the
monthly changes of GSI indices and proportions of
each maturity stage (Zhang et al., 2009).
RESULTS AND DISCUSSION
A twelve months long experiment was performed
with a view to observing length-weight
relationship and GSI of Hilsa, T. ilisha fishes in
Meghna river, Bangladesh. A total of 517
specimens (171 male and 346 female) were
collected and analyzed (Figure 1). Total length and
total body weight data of male hilsa fishes
collected over the period from January to
December 2013, power relationships between
them were estimated as BW = 0.01TL3.040
(R2=0.902) (Figure 2).The parameters ‘a’ and ‘b’
in the power curve equation derived from length-
weight relationships were estimated as: 0.01 and
3.04, respectively (Figure 2). The higher value of
‘b’ in males revealed that, the length-weight
relationships might be affected by the general
condition of appetite and gonadal contents of the
fish.
The correlation coefficient (0.902) showed that
there was a strong relationship between total
length and total body weight in the sample and its
positive value reflected that the slope is positive
(Figure 2).

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Table 1
Collection record of T. ilisha from January, 2013 to December, 2013.
Sampling
Date
No. of
Male
Size Range
No. of
Female
Size Range
TL (cm)
BW (g)
TL (cm)
BW (g)
January
19
30.2-36.5
300-500
25
25.7-45
350-1050
February
12
25.6-39.2
200-700
26
35-41.5
550-860
March
7
29.3-40.1
360-650
37
34.5-45.3
540-970
April
7
30.2-37.5
410-590
20
31.5-38.5
320-820
May
26
32.8-41
350-800
35
34.5-43
425-900
June
22
31.5-39.8
350-750
34
34-45.5
336-950
July
9
31.5-39.5
360-840
32
38.5-47.8
750-1260
August
11
32-40
350-850
29
35.3-44
600-950
September
19
26-37.5
220-750
29
34.5-43.5
490-1170
October
14
24.5-38
150-740
30
25.5-43
150-1000
November
16
20.9-39
300-750
33
28-39
250-860
December
9
32.7-39
390-800
16
36.4-41
600-985
Where, TL= Total length; BW= Body weight
Figure 1
Percentage composition of male and female T. ilisha
The relationships were significant at 95%
confidence level for T. ilisha, with r2 values being
greater than 0.196 and is applicable to the
population as a whole. The coefficient of
determination (0.902) explained that 90.20% of
the variation in body weight was due to the
variation in total length in the sample of hilsa, T.
ilisha collected over the period from January to
December 2013.
From the total length and total body weight data of
female hilsa fishes collected over the study period,
power relationships between them were estimated
as TL = 0.008BW3.078 and R2=0.822 (Figure 3).
0%
20%
40%
60%
80%
100%
120%
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Frequency (%)
Month
Female
Male

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Figure 2
The generalized relationship between total body
weight (g) and total length (cm) in the male, T.
ilisha.
The parameters ‘a’ and ‘b’ in the power curve
equation derived from length-weight relationships
were estimated as: 0.008 and 3.07, respectively
(Figure 3). The higher value of ‘b’ in females
revealed that, the length-weight relationships
might be affected by the general condition of
appetite and gonadal contents of the fish.
Figure 3
The generalized relationship between total body
weight (g) and total length (cm) in the female, T
ilisha
The correlation coefficient (0.822) shows that
there was a strong relationship between total
length and body weight in the sample and its
positive value reflected that the slope is positive
(Figure 3). The relationships were significant at
95% confidence level for T. ilisha, with r2 values
being greater than 0.196 and is applicable to the
population as a whole. The coefficient of
determination (0.822) explained that 82.2% of the
variation in body weight was due to the variation
in total length in the sample of hilsa, T. ilisha
collected over the period from January to
December 2013.
The length - weight relationship of male and
female of T. ilisha showed that the growth is
isometric. The correlation coefficient values were
very close to 0.99, which indicates that the
relationships between total length and weight of
this species was highly significant (p<.05). This
finding agrees with the results of Ahmed and Saha
(1996). The results clearly indicated that the mean
length of female was significantly higher than
male T. ilisha (p<.05). Roomiani et al. (2014) also
found same result for T. ilisha. Amin et al. (2009)
showed that the exponent ‘b’ usually lies between
2.5 and 4. The value of ‘b’ will be exactly ‘3’
when the growth is isometric. The value of ‘b’
differs not only between species but sometimes
also between the stock of the same species due to
sex, maturity, seasons and even time of day
because of changes in stomach fullness. The
regression coefficient ‘b’ of the length-weight
relationship of T.ilisha in the Khouzestan Province
of Iran lies between 2.68 to 3.16 as Amin et al.
(2005) suggested are reasonable values for this
species. Another studies in Bangladesh and India
(Ramakrishnaiah, 1972; Shafi and Quddus, 1974;
1978; Quddus et al., 1984b; Amin et al., 2002;
2004; 2005, Roomiani et al., 2014) found the ‘b’
of T.ilisha to be in the range 2.76-3.38. These
values are similar to those obtained for Meghna
river fishes from Chandpur.
The GSI value of male ranged from 0.11-12.3
(Figure 4). The GSI values in the months of
March, June and July were small ranging from
0.3-1.16, 0.16-0.89 and 0.36-0.7 respectively
(Figure 4). Specimens collected on January,
February, April and December were more or less
small and medium sized fish and GSI values
varied from 0.26-3.53, 0.47-1.82, 0.61-1.43 and
0.36-1.18 respectively, and some large GSI values
were also observed but these were in few fishes
(Figure 4). Fish caught on May, August and
October having medium and large GSI values
ranged from 0.17-7.68, 0.16-12.3 and 0.55-1.67
respectively (Figure 4).
y = 0.01x3.0402
R² = 0.9027
0
100
200
300
400
500
600
700
800
900
0 20 40 60
Body Weight (g)
Total Length (cm)
y = 0.0089x3.0788
R² = 0.8221
0
200
400
600
800
1000
1200
1400
0 20 40 60
Body Weight (g)
Total Length (cm)

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Figure 4
Monthly GSI variation in male, T. ilisha.
Figure 5
Monthly GSI variation in female, T. ilisha.
For female, the GSI values varied from 0.12-24
(Figure 5) throughout the sampling period.
Specimens collected on March, April, May and
August having small GSI varying from 0.12-11.05,
2.45-13.6.0.17-14.4 and 0.67-13.5 respectively;
though there were some large GSI values but these
were few (Figure 5). Female fish caught on
September, October, November and December
2013 comprised medium and large GSI values
varying from 5.97-18.96, 1.6-24, 5.27-10.71and
5.08-16.66 respectively (Figure 5). GSI values
were in the months of June, July and February
were having values ranging from 0.2-16.4, 3.64-15
and 0.59-21.5 respectively (Figure 5). Large GSI
values were observed in the months of October
and November in almost all cases.
The GSI values for females showed three peaks
apparently, those were in June, October and
February. The highest mean GSI value was
calculated in October. Male GSI showed the peaks
as well and those were observed in January,
September and October having highest in
September and second highest in October. Male
and female GSI data graphed in Figure 4 & 5
illustrated the trend of spawning season of the
species. Though the spawning of both male and
female occurs concurrently, since monthly mean
female GSI over the year peaked in October,
therefore, October was primarily assigned to the
spawning season of T. ilisha.
0
2
4
6
8
10
12
14
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
GSI (Gonadosomatic Index)
Month
0
5
10
15
20
25
30
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Gonado somatic Index (GSI)
Month

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Studies on sex ratio in T.ilisha have been made by
Shafi et al. (1974 and 1978), Quddus et al.
(1984a), Amin et al. (2005). These authors have
reported dominance of either males or females in
some months or seasons and showed the observed
sex ratio was significantly different from the
expected ratio of 1:1. Roomiani et al. (2014) also
found same result. The present findings on sex
ratio are generally consistent with those studies.
Change of sex ratio corresponding to the body
length is a vital parameter which may be directly
related with growth rate, natural and fishing
mortalities (Guoping et al., 2008). In this study,
the sex ratio of T. ilisha was M: F= 1:2. This sex
ratio was changed between different months, but
female predominate males. Dominance of females
over the males complies with the results of Amin
et al. (2005) (males to females 1:5.09).
Contradictory views have been expressed by
previous investigations on the sex ratio of T. ilisha
populations (Quddus et al., 1984a; Ahmed and
Saha, 1996). These variations may be caused by
males and females often moving in separate
shoals. Several reasons suggested for the unequal
sex ratios (Zhang et al., 2009).
Monthly variations in Gonadosomatic index (GSI)
of both sexes were quite apparent (Roomiani et al.,
2014). Maximum values were recorded in June
and May for male and female, respectively.
Changes in GSI indices are considered as a proof
that maturation season from March and spawning
started from April to July. Narejo et al. (2008)
found values of gonadosomatic index (GSI) for
male and female of T. ilisha from River Indus
were recorded for six months during summer from
April to September and in winter from October to
March. It was observed that in the females of both
types GSI values were higher in July and February
17.33 and 17.30, respectively. In summer
increasing trends in GSI values were recorded in
males and females from June to August with a
peak in July, while in case of winter T. ilisha the
GSI values were increasing from January to March
with peak in February. But in the present study
GSI was found highest in October and lowest in
December. In can be concluded that data on male,
female and combined fish functional length-weight
relationships are important for fish stock
assessment. This study will be helpful for fishery
managers to impose adequate regulations for
sustainable fishery management in Meghna river
as well as other rivers of Bangladesh.
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