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Gonadosomatic Index-based Size at First Sexual Maturity of the Catfish Eutropiichthys Vacha (hamilton, 1822) in the Ganges River (nw Bangladesh)

M. Y. Hossain
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi, Bangladesh

M. A. S. Jewel
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi, Bangladesh

L. Nahar
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi, Bangladesh

M. Mosaddequr Rahman
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi, Bangladesh

A. Naif
Department of Microbiology, College of Science, King Saud University, Riyadh, Saudi Arabia

J. Ohtomi
Faculty of Fisheries, Kagoshima University, Kagoshima, Japan

Abstract/ Executive Summary:

This study describes the size at first sexual maturity, length– weight relationships (LWR) in relation to size at first sexual maturity, and Fultons condition factor (K_F) of Eutropiichthys vacha in the Ganges River, northwestern Bangladesh. Sampling was done using traditional fishing gear including cast nets, square lift nets and conical traps during January and April, and July to December 2010. For each individual, total length (TL) was measured to the nearest 0.01 cm, and total weight (BW) was determined to the nearest 0.01 g. The gonadosomatic index (GSI) was calculated by the equation, GSI (%) = (Gonad weight in g ⁄ BW) · 100. The size at first sexual maturity of males and females was estimated by the relationship between gonadosomatic index and total length. A total of 583 specimens (289 males; 294 females) ranging from 8.30 to 27.00 cm TL and 3.16 to 159.50 g BW were analyzed. Sizes at first sexual maturity for male and female E. vacha were 13.15 and 14.00 cm TL, respectively. The analysis of covariance (ANCOVA) revealed significant differences in slope and intercept between early and late phases for males (F = 4.532, P < 0.001) and females (F = 21.984, P < 0.001). The K_F was not significantly correlated with TL for males (rs = 0.052; P = 0.378), but was highly correlated for females (rs = )0.165; P = 0.005). This study establishes a strong base for monitoring changes in length at first sexual maturity attributable to high fishing pressures or other reasons within the Ganges and associated river ecosystems.

Keywords: Gonadosomatic index, Sexual maturity, Eutropiichthys vacha, Bangladesh

Location: Rajshahi, Bangladesh.

Start Date: 00-07-2010

End Date: 00-12-2010

Program Area: Variety and Species

Commodity: Aquatic animal

Objectives:

To describe the size at first sexual maturity, length– weight relationships (LWR) in relation to size at first sexual maturity, and Fultons condition factor (KF) of Eutropiichthys ?vacha in the Ganges River, northwestern Bangladesh

Methodology:

This study was conducted in the lower part of the Ganges (known as the Padma River in northwestern Bangladesh), entering via India through the Rajshahi district (24⁰22' N; 88⁰35' E). Samples were collected from the fishing catch landed at Rajshahi city (Jhaj ghat, Binodpur), Bangladesh during January and April, and July to December 2010. The main gear used by the commercial fishers included traditional fishing gear such as jhaki jal (cast net), tar jal (square lift net), and dughair (conical trap). The fresh samples were immediately chilled in ice onsite and fixed in 10% buffered formalin upon arrival in the laboratory. All morphometric measurements were taken. All specimens were sexed by morphometric characteristics and gonad observation under a binocular microscope. Total length (TL) was measured to the nearest 0.01 cm for each individual using digital slide calipers (Mitutoyo, CD-15PS), and total weight (BW) measured using an electronic balance (Shimadzu, EB-430DW) with 0.01 g accuracy. Whole gonads were removed from each individual and weighed (GW) with an electronic balance to 0.001 g. The gonadosomatic index (GSI) was calculated by the equation, GSI (%) = (GW ⁄ BW) · 100. Size at first sexual maturity was estimated by the relationship between the gonadosomatic index and its total length for males and females separately. The relationship between length and weight was calculated using: W = a L^b, where W is the total (individual) weight (BW, g), L the total length (TL, cm), a is the intercept of the regression and b is the slope or regression coefficient. Parameters a and b of the weight–length relationship were estimated by linear regression analysis based on natural logarithms: ln(W) = ln(a) + b ln(L). Additionally, 95% confidence limits of the parameters a and b and the statistical significance level of r² (coefficient of determination) were estimated. Prior to the regression analysis of ln BW on ln TL, ln–ln plots of length and weight values were performed for visual inspection of outliers, with extremes excluded from the regression analyses. Fultons condition factor (KF) (Fulton, 1904) was calculated using the equation: K_F = 100 · (W ⁄ L³), where W is the total (individual) weight (BW, g) and L is the total length (TL, cm). The scale factor of 100 was used to bring the K_^F close to the unit factor. Statistical analyses were performed using GRAPHPAD PRISM 5 software. The Mann–Whitney U-test compared the mean value between sexes. The Spearman rank test correlated body measurements (e.g. TL, BW) and condition factors (K_F and KF). In addition, the parameters a and b of the LWR between sexes were compared by the analysis of covariance (ANCOVA). All statistical analyses were considered significant at 5% (P < 0.05).

Source of Information: J. Appl. Ichthyol. 28 (2012), 601–605

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

This study provides crucial biological parameters, including the size at sexual maturity for E. vacha in the Ganges River, which are important indicators of minimum permissible capture sizes. Moreover, this data establishes a strong base for monitoring changes in length at first sexual maturity attributable to high fishing pressure or other factors within the Ganges River and associated ecosystems.

Knowledge Management: Journal