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Population Biology of the Indian River Shad, Gudusia Chapra (clupeidae) in the Old Brahmaputra River, North-eastern Bangladesh

FERDOUS AHAMED
Department of Fisheries Management Patuakhali Science and Technology University Patuakhali-8602, Bangladesh

ZOARDER FARUQUE AHMED
Department of Fisheries Management Bangladesh Agricultural University Mymensingh 2202 Bangladesh

MD. YEAMIN HOSSAIN
Department of Fisheries, Faculty of Agriculture University of Rajshahi Rajshahi 6205 Bangladesh

JUN OHTOMI
Faculty of Fisheries Kagoshima University 4-50-20 Shimoarata Kagoshima 890-0056 Japan

Abstract/ Executive Summary:

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

Location: Old Brahmaputra River, Bangladesh.

Start Date: 00-01-2009

End Date: 00-12-2009

Program Area: Conservation and Biodiversity

Commodity: Aquatic animal

Objectives:

To provide information about the population biology of G. chapra 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 and information for the sustainable management of this species.

Methodology:

The present study was conducted in the Old Brahmaputra River of Bangladesh which is comprised of two channels: A main channel, the Jamuna which running through Bangladesh, and an old channel, commonly known as the Old Brahmaputra River running through the northeastern district of Mymensingh, Bangladesh, straddling 23º 58´ and 25º 25´ N, and 89º 38´ and 91º 15´ E. Monthly samples were collected from several predetermined sites of the river section passing through Bangladesh Agricultural University campus during January-December 2009. The sampling was conducted from a boat using a combination of fine meshed cast nets and seine nets of <2 mm mesh size in order to include all size groups within the population in the catch. Monthly water temperature was also recorded at each sampling. All specimens were preserved in ice and transferred to the laboratory prior to analysis. The standard length (SL) of all individuals was measured to the nearest 1 cm using a measuring scale, while body weight (BW) was recorded using a digital balance (Shimadzu, EB-430DW, Japan) to 0.01 g accuracy. Sexing was conducted by incision of the abdomen of each individual and visual inspection of the gonad. All fat, connective tissue and blood vessels were carefully removed from the gonads and the weight of the gonads measured to the nearest 0.001 g. Monthly sex ratio (females/total) was calculated and results were analyzed by use of a χ² test (1:1; p<0.05). Temporal changes in the population structure of G. chapra were investigated by examining SL frequency distributions, which were obtained by sex using 0.5 cm interval on pooled data for the whole sampling period as well as by group for each month. The gonadosomatic index (GSI) was calculated as: GSI (%) = (GW ⁄ BW) × 100. Female size at first sexual maturity was estimated by the relationship between the GSI and SL. Spawning season was estimated based on the monthly variations of GSI. The relationship between BW and SL was calculated using the equation: BW = a SL^b, where a and b are the intercept and slope, respectively, of the linear regression analysis equation based on natural log equations of the relationship between BW and SL as follows: ln (BW) = ln (a) + b ln (SL). Significant deviation of b value from the theoretical isometric value (b = 3) indicates either positive (b > 3) or negative (b < 3) allometric growth, which was verified with Student’s t-tests. Analysis of covariance (ANCOVA) was used to test for significant differences in slopes and intercepts between sexes. Fulton’s condition factor (K) was estimated using the equation: K = (BW ⁄ L³) × 100 for both monthly and in terms of size (SL in cm) class.

Source of Information: Sains Malaysiana 43(11)(2014): 1645–1655

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

This is the first comprehensive study on the biological aspects of this shad fish in the Old Brahmaputra River, NE Bangladesh. The findings of this study would be useful for fishery biologists/managers to impose adequate regulations for conservation of this critically endangered fishery in Bangladesh and neighbouring countries.

Knowledge Management: Journal