CORE Metadata, citation and similar papers at core.ac.uk Provided by UKM Journal Article Repository Sains Malaysiana 43(11)(2014): 1645–1655 Population Biology of the Indian River Shad, Gudusia chapra (Clupeidae) in the Old Brahmaputra River, North-Eastern Bangladesh (Populasi Biologi Shad, Sungai India Gudusia chapra (Clupeidae) di Sungai Brahmaputra Lama, Timur Laut Bangladesh) FERDOUS AHAMED*, ZOARDER FARUQUE AHMED, MD. YEAMIN HOSSAIN & JUN OHTOMI ABSTRACT Population biology including population structure, reproduction, length-weight relationship and condition factor of a commercially important clupeid freshwater fish,Gudusia chapra was studied in the Old Brahmaputra River, Bangladesh during January-December 2009. In the present study, a total of 2032 specimens (1091 male; 941 female) were collected. The overall sex ratio showed significant difference from the expected value 1:1 (male: female = 1:0.86, χ2 = 11.07, p<0.001). Length-frequency distribution showed a size predominance of females over males, where mean female size consistently exceeded that of males throughout the year. Female size at first sexual maturity was estimated as 8.3 cm in standard length (SL). Monthly gonadosomatic index (GSI) was higher during March-September with a peak in April, indicating this was the main spawning season. The allometric coefficient b of the length-weight relationship (LWR) indicated negative allometric growth in males and females, but the analysis of covariance (ANCOVA) showed significant differences in slope and intercept between the sexes (p<0.001). Fulton’s condition factor by months and SLs varied in both sexes and was attributed to variations in GSI with maturity. Keywords: Clupeidae; gonadosomatic; Gudusia chapra; index; management; population biology ABSTRAK Populasi biologi termasuk struktur populasi, pembiakan, hubungan panjang-berat dan keadaan faktor yang penting secara komersial ikan klupeid air tawar, Gudusia chapra telah dikaji di Sungai Lama Brahmaputra, Bangladesh sepanjang Januari-Disember 2009. Dalam kajian ini, sejumlah 2032 spesimen (1091 jantan; 941 betina) telah dikumpulkan. Nisbah jantina secara keseluruhan menunjukkan perbezaan yang ketara daripada jangkaan nilai 1:1 (jantan: betina = 1:0.86, χ2 = 11.07, p<0.001). Pembahagian panjang-kekerapan menunjukkan saiz betina kepradominaan berbanding jantan dengan purata saiz betina secara konsisten melebihi jantan sepanjang tahun. Saiz kematangan seksual pertama pada betina adalah dianggarkan sebagai 8.3 cm mengikut piawai panjang (SL). Indeks bulanan gonadosomatik (GSI) adalah lebih tinggi semasa bulan Mac-September dengan puncak pada bulan April yang menunjukkan ini adalah musim bertelur yang utama. Pekali hubungan alometrik b panjang-berat (LWR) menunjukkan pertumbuhan alometrik negatif dalam jantan dan betina, tetapi analisis kovarians (ANCOVA) menunjukkan perbezaan yang signifikan antara jantina dalam cerun dan pintasan (p<0.001). Faktor keadaan Fulton mengikut bulan dan SLs berubah dalam kedua-dua jantina dan ini disebabkan oleh perubahan dalam GSI dengan matang. Kata kunci: Biologi penduduk; Clupeidae; gonadosomatik; Gudusia chapra; indeks; pengurusan INTRODUCTION In Bangladesh, G. chapra is one of the important small The Indian River shad, Gudusia chapra (Hamilton 1822), indigenous fish species reported as both an important food is a freshwater clupeid species which is widely distributed resource and a crucial source of micronutrients essential in the river systems of India and Bangladesh affluent to the in preventing malnutrition and vitamin and mineral Bay of Bengal; principally the Ganges and Brahmaputra deficiencies in the rural communities, particularly among (Whitehead 1985). The species has also been reported from women and children (Thilsted 2003; Thilsted et al. 1997). Nepal and Pakistan (Menon 1999; Shrestha 1994). The It is commercially important as a target species for the species also inhabits lakes, ponds, ditches and inundated small-scale fishermen (Ahmed et al. 2007; Craig et al. fields (Rahman 1989). The species presents an important 2004; Kibria & Ahmed 2005). fishery in the artisanal fisheries of the Indian sub-continent Several studies on the biological aspects of G. chapra, and is an important source of livelihood for many of including maturity and fecundity (Chondar 1977; Jhingran the subsistence and artisanal fisher folks (Daniels 2002; & Verma 1967; Mustafa & Ansari 1983; Quddus et al. Jayaram 1999; Talwar & Jhingran 1991). 1990), morphology, meristic and non-meristic characters 1646 (Chondar 1976, 1975), fecundity (Chondar 1977; Mustafa maturity was estimated by the relationship between the & Ansari 1983; Quddus et al. 1990), gonadosomatic GSI and SL. Spawning season was estimated based on the index and fecundity (Kabir et al. 1998), age and growth monthly variations of GSI. (Narejo et al. 2000), biology (Vinci et al. 2005), growth The relationship between BW and SL was calculated and reproduction (Ahmed et al. 2007), length-weight using the equation: BW = a SLb, where a and b are the relationships (Hossain et al. 2009; Sani et al. 2010) and intercept and slope, respectively, of the linear regression size at sexual maturity and fecundity (Hossain et al. 2010) analysis equation based on natural log equations of the have been conducted. relationship between BW and SL as follows: ln (BW) = ln The Old Brahmaputra River is considered as an (a) + b ln (SL). Significant deviation of b value from the important spawning and feeding ground for riverine theoretical isometric value (b = 3) indicates either positive fishes of Bangladesh and a large numbers of these species (b > 3) or negative (b < 3) allometric growth (Tesch 1971), including G. chapra fished by both small and large-scale which was verified with Student’s t-tests (Sokal & Rohlf fisheries throughout the year (Hossain & Ahmed 2008). 1981). Analysis of covariance (ANCOVA) (Zar 1984) However, there is no published report on the biology of G. was used to test for significant differences in slopes and chapra from the Old Brahmaputra River of Bangladesh, intercepts between sexes. Fulton’s condition factor (K) was which attracted our attention extensively. Therefore, the estimated using the equation: K = (BW ⁄ L3) × 100 for both present study describes the population biology of G. chapra monthly and in terms of size (SL in cm) class. including sex ratio, population structure, size at first sexual maturity, spawning season, length-weight relationship and condition factor in order to provide the much needed data RESULTS and information for the sustainable management of this A total of 2032 specimens of G. chapra were collected species. during this study, with 1091 (53.7%) males and 941 (46.3%) females. The SL ranged at 3.5-12.5 cm in males and 3.1-13.7 cm in females, whereas BW ranged at 0.80-33.01 g MATERIALS AND METHODS and 0.91-44.54 g for male and female respectively (Table The present study was conducted in the Old Brahmaputra 1). The sex ratio was 1:1 for almost all the year (Figure 1), River of Bangladesh which is comprised of two channels: except in June, August, September and December when A main channel, the Jamuna which running through males were significantly more abundant than females Bangladesh, and an old channel, commonly known as the (χ2 test, p<0.05). However, the overall sex ratio showed Old Brahmaputra River running through the northeastern significant difference from the expected value of 1:1 district of Mymensingh, Bangladesh, straddling 23º 58´ (male:female = 1:0.86, χ2 = 11.07, p<0.001) (Figure 1). and 25º 25´ N, and 89º 38´ and 91º 15´ E. The pooled size-frequency distribution was polymodal Monthly samples were collected from several and asymmetrical for larger sizes, with the main mode predetermined sites of the river section passing through peaking at approximately 7 cm for both sexes (Figure Bangladesh Agricultural University campus during 2). Monthly changes in size-frequency distributions by January-December 2009. The sampling was conducted sex showed the occurrence of different size groups of G. from a boat using a combination of fine meshed cast nets chapra in the population during the year (Figure 3). There and seine nets of <2 mm mesh size in order to include all was a size predominance of females over males, with mean size groups within the population in the catch. Monthly female size consistently exceeding that of male throughout water temperature was also recorded at each sampling. the year. All specimens were preserved in ice and transferred to The relationship between SL and GSI of female G. the laboratory prior to analysis. The standard length (SL) chapra is shown in Figure 4. The lowest and highest GSI of all individuals was measured to the nearest 1 cm using recorded during this study was 0.02 and 12.64 respectively. a measuring scale, while body weight (BW) was recorded The GSI of < 8 cm SL- females was low (<4.0). However, using a digital balance (Shimadzu, EB-430DW, Japan) to the GSI rose sharply at around 8.3 cm SL. Therefore, the 0.01 g accuracy. Sexing was conducted by incision of the size at first sexual maturity of G. chapra was considered abdomen of each individual and visual inspection of the to be 8.3 cm SL. gonad. All fat, connective tissue and blood vessels were The monthly mean GSI with minimum and maximum carefully removed from the gonads and the weight of the values of female G. chapra were plotted (Figure 5). The gonads measured to the nearest 0.001 g. mean GSI varied from 0.82 in January to 4.83 in April. The Monthly sex ratio (females/total) was calculated and GSI value began to rise from March and remained high until results were analyzed by use of a χ2 test (1:1; p<0.05). September with a peak in April. The GSI then decreased Temporal changes in the population structure of G. chapra from October and remained low until February. were investigated by examining SL frequency distributions, The relationships between SL and BW indicated which were obtained by sex using 0.5 cm interval on pooled negative allometric growth both in males and females as the data for the whole sampling period as well as by group for allometric coefficientb values were significantly different each month.