Population Structure, Growth and Length Weight Relationship of Sergestid Shrimps
(Acetes spp.) from the Coastal Waters of Malacca, Peninsular Malaysia
(Struktur Populasi, Pertumbuhan dan Hubungan Panjang-Berat Udang Sergestid (Acetes spp.) di Perairan Selat Melaka, Semenanjung Malaysia)
S. M. NURUL AMIN, AZIZ ARSHAD, SITI SHAPOR SIRAJ & JAPAR SIDIK BUJANG
ABSTRACT
The size frequency distribution for age structure and length weight relationship of three species of the genus Acetes from the coastal waters of Malacca, Peninsular Malaysia are reported. The length frequency distribution for A. indicus suggested that the population consisted of two dominant age groups with mean at 20.80 (± 2.42) mm and 29.85 (± 2.79) mm of total length, respectively. The population of A. japonicus consisted of maximum two age groups, with means of 15.18 (± 0.90) mm and 21.56 (± 1.03) mm of total length. The population of A. intermedius also consisted of maximum two age groups, with means of 19.18 (± 2.45) mm and 26.92 (±2.82) mm of total length. The positive allometric nature of growth for A. indicus was observed in the coastal waters of Malacca. But isometric nature of growth was found in combined sexes of A. japonicus. The positive allometric nature of growth was observed in female and both sexes of
A. intermedius. There were signiicant difference between males and females size-frequency distribution of A. indicus (Kolmogorov-Smirnov test: dmax= 0.42, P < 0.001), A. japonicus (Kolmogorov-Smirnov test: dmax = 0.39, P < 0.001) and A. intermedius (Kolmogorov-Smirnov test: dmax = 0.40, P < 0.001). The signiicant differences were observed between mean total length of female and male of A. indicus, A. japonicus and A. intermedius (t-test, P < 0.001).
Keywords: Population structure; Acetes spp; Penisular Malaysia ABSTRAK
Taburan frekuensi bagi struktur umur dan hubungan panjang berat bagi tiga spesies genus Acetes dari perairan pantai
Melaka, Semenanjung Malaysia dilaporkan. Taburan frekuensi panjang Acetes indicus menunjukkan yang populasinya terdiri daripada dua kumpulan umur dominan dengan nilai purata 20.80 (± 2.42) mm dan 29.85 (± 2.79) mm setiap satu daripada jumlah keseluruhan panjang badan. Populasi A. japonicus pula terdiri daripada dua kumpulan umur maksimum, dengan nilai purata 15.18 (± 0.90) mm dan 21.56 (± 1.03) mm daripada jumlah keseluruhan panjang. Populasi A. intermedius juga didapati terdiri daripada dua kumpulan umur maksimum, dengan nilai purata 19.18 (± 2.45) mm dan 26.92 (± 2.87) mm daripada jumlah keseluruhan panjang badan. Kajian menunjukkan yang populasi A. indicus daripada perairan Pantai Melaka diperhatikan mempunyai pertumbuhan semulajadi alometrik yang positif
manakala pertumbuhan semulajadi isometrik didapati pada kedua-dua jantina A. japonicus. Pertumbuhan semulajadi
alometrik positif diperhatikan pada yang betina dan juga kedua-dua jantina A. intermedius. Terdapat perbezaan bererti
pada taburan frekuensi saiz antara jantan dan betina A. indicus (ujian Kolmogorov-Smirnov: dmax= 0.42, P < 0.001), A. japonicus (ujian Kolmogorov-Smirnov: dmax = 0.39, P < 0.001) dan A. intermedius (ujian Kolmogorov-Smirnov: dmax = 0.40, P < 0.001). Perbezaan bererti didapati pada jumlah purata panjang keseluruhan betina dan jantan A. indicus, A. japonicus dan A. intermedius (t-test, P < 0.001).
Kata kunci: Struktur populasi; Acetes spp.; Semenanjung Malaysia
INTRODUCTION
The shrimp of the genus Acetes, is mainly used in subsistence
isheries and is, therefore, commercially important in the
Peninsular Malaysia (Tham 1950; Pathansali 1966; Johnson 1976). Knowledge on the shrimp’s biology and population characteristics are important if proper management of those
resources are to be effective. Age in crustacean is dificult
to estimate because exoskeletons are lost during moulting process. Thus, analysis of length-frequency data has been used to identify year classes (Amin & Zafar 2003; Zafar
et al. 1998b). Length weight relationships are useful for a wide number of studies, such as estimating growth rates,
age structure and other aspects of ish/shrimps population
dynamics (Tsoumani et al. 2006). Length-weight relationships have been extensively used for estimation
of weight from length due to technical dificulties and the amount of time required to record weight in the ield
the condition factors of the aquatic species. In addition to the above, length-weight relationships are useful for between region comparisons of life histories of a certain species. Therefore, the present study has been undertaken to estimate the size frequency distribution for age structure and length weight relationships to know the relative growth pattern of three species of the genus Acetes (A. indicus, A. japonicus and A. intermedius) from the coastal waters of Malacca, Peninsular Malaysia.
METHODOLOGY
SAMPLING AND DATA COLLECTION
Monthly samples of Acetes spp were collected from Klebang Besar (N 020 13.009′ & E 1020 11.921′)in the Malacca coastal waters, Straits of Malacca (Figure 1) between February 2005 and January 2006. Triangular shape push net (mesh size 3.2 cm at anterior section, 0.75 cm at middle and 0.5 cm at cod end) were used to collect the samples of Acetes. The ishing effort was
one man per hour and towing length was approximately 1000 m along the coast of Klebang Besar, Malacca. After
collection, samples were ixed in 10% formalin solution in the ield and analyzed after 2-3 days of preservation. In
the laboratory, Acetes spp were identiied using a Nikon dissecting microscope (Nikon-122764, Japan). The works
of Omori (1975) were followed during the identiication
of Acetes spp. Total lengths (TL) of each individual (males and females) were measured from the tip of the rostrum to the tip of the telson to the nearest 0.1 mm and total weight was taken by an electronic balance of 0.001 gm accuracy during February 2005 and January 2006.
DATA ANALYSIS
To estimate the population structure, the length-frequency data were analyzed by using the MINITAB Version 14 and SPSS Version 11.5. The differences in the size-frequency distributions of population between sexes were determined by the Kolmogorov-Smirnov two-sample test (Sokal & Rohlf 1995). Student’s t-test was used for comparison of the mean total length of males and females (Zar 1996).
FIGURE 1. Geographical location of the sampling station (
•
), Klebang Besar in theSize-frequency distributions were plotted for each month. Bhattacharya’s method, implemented from the package FiSAT II Version 1.1.2 (Gayaniloet al. 2002) was used to identify the modes in the polymodal length-frequency distributions of A. indicus. All the identiied size/ age groups were derived from at least three consecutive points and selection of the best results was based on the following criteria:
1. the values of separation index (SI) for the different age groups;
2. the number of the identiied age groups and
3. the standard deviation (SD)(Gayanilo et al. 1989). To establish the length-weight relationship, the commonly used relationship W = a Lb was applied (Ricker 1975; Quinn II & Deriso 1999), where W is the weight (mg), L is the total length (mm), a is intercept (condition
factor) and b is the slope (growth coeficient, i.e., shrimp
relative growth rate). The parameters a and b were estimated by least squares linear regression on log-log transformed data: Log10 W = Log10 a + b Log10 L. The coeficient of determination (r2) was used as an indicator of the quality of the linear regression (Scherrer, 1984). Additionally, 95% conidence limits of the parameters a and b and the statistical signiicance level of r2 were estimated.
RESULTS
SIZE FREQUENCY STRUCTURE
Acetes indicus Total number of individuals collected for
this study was 814 (33.22%) for male and 1636 (66.78%)
for female, respectively. According to the size-frequency
distribution, there was signiicant difference between males
and females (Kolmogorov-Smirnov test: dmax = 0.396, P < 0.001) (Figure 2a). In males, the minimum and maximum total lengths were 13 mm and 30.5 mm, and in females, they were 14 mm and 41 mm respectively (Table 1). The mean total lengths were 21.37 (± 2.86) mm and 25.44 (± 4.66) mm for male and female, respectively. The mean total length of female was 4.08 mm taller than that of the male (Figure 3a),
and it was signiicantly different (t-test, P < 0.001). Monthly
size frequency distributions are given in Figure 4. The length frequency distribution of 12 months suggested that the population consisted of two age groups, with means of 20.80 (± 2.42) mm and 29.85 (± 2.79) mm of total length. Acetes japonicas A total number of individuals collected
for this study was 1079 (30.76%) for male and 2429 (69.24%) for female, respectively. According to the annual size-frequency distribution, there was signiicant difference
between the males and females (Kolmogorov-Smirnov test: dmax = 0.39, P < 0.001) (Figure 2b). The mean total lengths were 14.83 (± 2.03) mm and 17.58 (± 3.77) for male and female, respectively. In the males, the minimum and maximum total lengths were 8 mm and 20 mm, and in the females, they were 9.50 mm and 29 mm, respectively (Table 1). The mean total length of the female was 2.75 mm longer
than that of the male (Figure 3b) and it was signiicantly
different (t-test, P < 0.001). Monthly size frequency
distributions (Figure 5) identiied the modal lengths with
cohorts in different months. The length frequency distribution of different months suggested that the population consisted of maximum two age groups, with means of 15.18 (± 0.90) mm and 21.56 (± 1.03) mm of total length.
FIGURE 3. Box plots of male and female Acetes indicus (a),Acetes japonicus (b) and Acetes intermedius (c) from the coastal waters of Malacca
Descriptive Sex A. indicus A. japonicus A. intermedius
M 21.37 ± 2.86 14.83 ± 2.03 22.15 ± 2.37
Mean ± SD of TL (mm) F 25.44 ± 4.66 17.58 ± 3.77 24.52 ± 4.09
B 24.06 ± 4.56 16.79 ± 3.59 23.88 ± 3.85
M 13.00 – 30.50 8.00 – 19.00 15.00 – 27.50
TL range (mm) F 14.00 – 40.00 9.50 – 28.00 13.50 – 33.00
B 13.00 – 40.00 8.00 – 28.00 13.50 – 33.00
M 9.50 – 174.10 4.20 – 33.80 13.60 – 103.50
Weight range (mg) F 13.30 – 430.00 4.10 – 102.70 11.80 – 206.20
B 9.50 – 430.00 4.10 – 102.70 11.80 – 206.20
M 1628 1079 269
Sample number (N) F 3272 2431 726
B 4900 3510 995
Abbreviation: SD-standard deviation; M-male; F-female and B-both
Acetes intermedius Total number of individuals collected
for this study was 269 (27.04%) for male and 726 (72.96%)
for female, respectively. According to the annual
size-frequency distribution, there was signiicant difference
between males and females (Kolmogorov-Smirnov test: dmax= 0.403, P < 0.001) (Figure 2c). The mean total lengths were 22.15 (± 2.373) mm and 24.517 (± 4.091) mm for males and females, respectively (Table 1). In males, the minimum and maximum total lengths were 15 mm and 27.50 mm, and in females, they were 13.50 mm and 33 mm, respectively (Table 1). The mean total length of female was 2.37 mm longer than that of the male (Figure
3c), and it was signiicantly different (t-test, P < 0.001). Monthly size frequency distributions (Figure 6) identiied
the modal lengths with cohorts in different months. The length frequency distribution of different months suggested that the population consisted of maximum two age groups, with means of 19.18 (± 2.58) mm and 26.92 (± 2.82) mm of total length.
LENGTH-WEIGHT RELATIONSHIPS
The parameters of total length-body weight relationships of Acetes spp. for different groups (males, females and both sexes) are presented in Table 2. The regression between total length (TL) and total weight (TW) for the males and females showed positive relationship, respectively (Figure7 and Figure 8 for A. indicus, Figure 9 and Figure 10 for A. FIGURE 4. Monthly size frequency distributions for both sexes of A. indicus from the
FIGURE 5. Monthly length frequency distributions for both sexes of A. japonicus caught between February 2005 and January 2006 in the coastal waters of Malacca
FIGURE 7. Length weight relationship of male A. indicus in the coastal waters of Malacca (Logarithmic and arithmetic scale)
FIGURE 9. Length weight relationship for male A. japonicus in the coastal water of Malacca, Peninsular Malaysia (Logarithmic and arithmetic scale)
FIGURE 8. Length weight relationship of female A. indicus in the coastal waters of Malacca (Logarithmic and arithmetic scale)
T
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t
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FIGURE 10. Length weight relationship for female A. japonicus in the coastal water of Malacca, Peninsular Malaysia (Logarithmic and arithmetic scale)
japonicus and Figure 11 and Figure 12 for A. intermedius). The length-weight relationship equations of Acetes spp. were established are presented in Table 3.
DISCUSSION
The size structure of the population of A. indicus, A. japonicus and A. intermedius in the investigated area consists of a relatively higher percentage of females than males. Females attained a greater size indicating a size
dimorphism. The growth coeficient ‘b’ of length-weight
relationship generally lies between 2.5 and 3.5 and the relation is said to be isometric when it is equal to 3 as reported for most aquatic organisms (Carlander 1977; Le Cren, 1951). Table 4 summarizes previous published
values of the coeficients a and b for the genus Acetes and the values of b show considerable variation, ranging from 2.155 in A. japonicus (Lei 1988) to 3.108 in A. indicus (present study).
The estimated b (3.411) for the combined sexes of A. indicus lies between the values mentioned by Carlander
(1977) and Ecoutin et al. (2005) and signiicantly higher than isometric value (3) at 5% level. This indicates the
positive allometric nature of growth for A. indicus in the coastal waters of Malacca.
The estimated b is 3.063 for combined sexes of A. japonicus and it lies between the values mentioned by Carlander (1977) and Ecoutin et al. (2005), which is not
signiicantly higher than isometric value (3) at 5% level.
This indicates the isometric nature of growth in combined sexes of A. japonicus. In the case of males, the estimated b
is 2.3215 and it is signiicantly lower from isometric value (3) at 5% level. The relationship between total lengths
against total weight suggested that as total length increases weight is heavier in females than in males of A. japonicus. Regression analysis on the log-transformed data showed a strong relationship of both sexes of A. japonicus (r 2 = 0.82 for males and r2 = 0.94 for females) and signiicant (P < 0.05).
Species Sex N a b (SE) 95% CI of b Growth type
M 1628 0.0019 3.307 (0.05) 3.211-3.403 Allometric (+)
A. indicus F 3272 0.0011 3.472 (0.25) 3.422-3.521 Allometric (+)
B 4900 0.0014 3.411 (0.02) 3.371-3.451 Allometric (+) M 1079 0.0293 2.3215 (0.04) 2.250-2.393 Allometric (-)
A. japonicus F 2431 0.0028 3.186 (0.016) 3.155-3.218 Allometric (+)
B 3510 0.004 3.063 (0.015) 3.034-3.092 Isometric
M 269 0.0049 2.979 (0.09) 2.798-3.159 Isometric
A. intermedius F 726 0.0024 3.227 (0.03) 3.159-3.296 Allometric (+)
B 995 0.0021 3.249 (0.03) 3.185-3.312 Allometric (+)
TABLE 2. Length-weight relationship parameters of A. indicus, A. japonicus and A. intermedius from the coastal waters of Malacca, Peninsular Malaysia
N-sample size; a and b-parameters of the length-weight relationship; SE-standard error of the slope b; CI-coeficient of interval; M-male;
L
FIGURE 11. Length weight relationship for male A. intermedius in the coastal water of Malacca, Peninsular Malaysia (Logarithmic and arithmetic scale)
FIGURE 12. Length weight relationship for male A. intermedius in the coastal water of Malacca, Peninsular Malaysia (Logarithmic and arithmetic scale)
Species Sex Length-weight relationship equations r2
M Log TW = 3.307 Log TL – 2.7136 0.85 (P < 0.05)
TABLE 3. Length weight relationship equations of A. indicus, A. japonicus and A. intermedius from the coastal waters of Malacca, Peninsular Malaysia
The estimated b of females’ A. intermedius is 3.227 and it lies between the values mentioned by Carlander (1977) and Ecoutin et al. (2005), which is signiicantly
higher than isometric value (3) at 5% level. This indicates
the positive allometric nature of growth for female’s A. intermedius. In case of males, the estimated b is 2.979 and
it is not signiicantly lower from isometric value (3) at 5%
level. The relationship between total lengths against total weight suggested that as total length increases weight is heavier in females than in males. Regression analysis on the log-transformed data showed a strong relationship of both sexes of A. intermedius (r 2 = 0.80 for males and r2 = 0.92 for females) and signiicant (P < 0.05).
CONCLUSION
The size structure of the population revealed that a relatively higher percentage of females than males in the three species of Acetes. The length frequency distribution of 12 months for A. indicus suggested that the population consisted of one dominant age group. The positive allometric nature of growth is observed for A. indicus in the coastal waters of Malacca. It is revealed from length frequency distributions that the population of A. japonicus consisted of maximum two age groups, with means of 15.18 (± 0.90) mm and 21.56 (± 1.03) mm of total length. The isometric nature of growth was found in the combined sexes of A. japonicus. The length frequency distribution of different months for A. intermedius suggested that the population consisted of maximum two age groups, with means of 19.18 (± 2.58) mm and 26.92 (± 2.82) mm of total length. Both sexes of A. intermedius showed positive allometric nature of growth in the coastal waters of Malacca.
ACKNOWLEDGEMENT
This work is part of a PhD thesis funded by the Ministry of Science, Technology and Innovation (MOSTI), Malaysia (Grant No. 05-01-04-SF0613). Special thanks to
Universiti Putra Malaysia for providing partial inancial
support through Graduate Research Fellowship (GRF)
during the study period. In addition, thanks go to Mr.
Ibrahim, isherman and Mr. Perumal, Science Oficer of
Marine Science Laboratory and Aquaculture, Institute of Bioscience, UPM for the assistance during ield sampling.
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Malaysia A. japonicus 0.004 3.063 0.93 Present study
Malaysia A. intermedius 0.0021 3.249 0.91 Present study
Bangladesh A. indicus 0.0047 3.108 0.98 Zafar et al. (1997)
Bangladesh A. chinensis 0.0107 2.908 0.98 Zafar et al. (1998a)
Bangladesh A. erythraeus 0.0051 3.106 0.99 Zafar et al. (1998b)
China A. joponicus 0.1302 2.155 - Lei (1988)
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Japan A. sibogae 0.0085 2.985 0.98 Ikeda & Raymont (1989)
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Aziz Arshad, Siti Shapor Siraj & Japar Sidik Bujang Department of Biology
Faculty of Science Universiti Putra Malaysia
43400 UPM Serdang, Selangor D. E.
MALAYSIA
S.M. Nurul Amin
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong-4331 Bangladesh
