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Growth, Condition, Maturity and Mortality of the Gangetic Leaffish Nandus Nandus (hamilton, 1822) in the Ganges River (northwestern Bangladesh)

Md. Yeamin Hossain*
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi 6205, Bangladesh

Md. Alomgir Hossen
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi 6205, Bangladesh

Dalia Khatun
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi 6205, Bangladesh

Fairuz Nawer
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi 6205, Bangladesh

Most. Farida Parvin
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi 6205, Bangladesh

Obaidur Rahman
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi 6205, Bangladesh

Md. Akhtar Hossain
Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi 6205, Bangladesh

Abstract/ Executive Summary:

The Gangetic leaffish, Nandus nandus (Hamilton, 1822) is an important nutritionally precious food fish in south Asian countries. This is the first inclusive explanation on population parameters of N. nandus i.e., population structure (LengthFrequency Distributions, LFDs), growth (Length-Weight and Length-Length Relationships; LWRs, LLRs), condition factors (allometric, KA; Fulton's, KF; relative, KR; relative weight, WR; and form factor, a3.0), reproduction (first sexual maturity, Lm) and natural mortality (MW) in the Ganges River, northwestern (NW) Bangladesh. Samples were collected using different fishing gears from April 2014-March 2015. Total Length (TL) and Standard Length (SL) were measured for each individual by digital slide calipers, while individual Body Weight (BW) was weighed by a digital balance. A total of 125 individuals ranging from 3.0-15.1 cm TL and 0.30-52.10 g BW were analyzed in the present study. The 7.00-8.99 cm TL was a numerically leading group of the total population. Allometric coefficient (b) of LWRs indicate positive allometric growth (b>3.0) for TL vs. BW and isometric growth (b=3.0) for SL vs. BW relationship. Additionally, the b value for LLR also shows the same growth pattern. In the present study, among four types of condition factors KF (ranged from 1.258 to 1.336) was best for the wellbeing of N. nandus in the Ganges River. Wilcoxon signed-rank test indicated that, the WR did not show any significant difference from 100 (p = 0.325), representing the balanced habitat for N. nandus. The a3.0 was 0.0159 indicating this fish is short and deep in body shape and the Lm was 9.10 (~ 9.00) cm TL and the MW was estimated as 1.33 y1. The results would be good strategy for the conservation of this species in the Ganges River and the surrounding ecosystem

Keywords: Nandus nandus, Growth, Condition, Maturity, Mortality, Ganges River.

Location: Ganges River (Lat. 24o 35' N; Long. 88o 64' E) NW Bangladesh

Start Date:

End Date:

Program Area: Animal Health and Management

Commodity: Fish

Objectives:

The objective of the present study is to depict the population parameters of N. nandus including growth pattern (Length-Weight Relationships, LWRs), reproduction (size at sexual maturity, Lm), and natural mortality (MW) from the Ganges River, northwestern (NW) Bangladesh using a number of specimens with small to big sizes over a one-year study period. Also, the condition of N. nandus was estimated through multi-models.

Methodology:

2.1. Study Site and Sampling The present study was carried out in the Ganges River (Lat. 24^o 35′ N; Long. 88^o 64′ E) NW Bangladesh. A total of 125 individuals of N. nandus were occasionally collected from the fishermen during April 2014 to March 2015. The fishes were caught using different types of traditional fishing gears i.e., gill net, cast net, square lift net, etc. Samples were instantly chilled in ice on site and preserved with 10% buffered formalin upon arrival in the laboratory. 2.2. Fish Measurement Total Length (TL) and Standard Length (SL) were measured to the nearest 0.01 cm using digital slide calipers and total Body Weight (BW) was weighed by an electronic balance with 0.01 g accuracy for each individual. 2.3. Growth Pattern The length-frequency distribution for N. nandus was constructed using 1 cm intervals of TL. The growth pattern was determined through LWR with the equation: BW= a*(TL)b where BW is the total body weight (g) and TL is the total length (cm). The parameters a and b were calculated by linear regression analyses based on natural logarithms: ln (W) = ln(a) + b ln(L). Extremes outliers were deleted from the regression analyses according to Froese (2006). Additionally, on the basis of the b values of LLR (TL vs. SL) growth pattern of N. nandus was determined. 2.4. Condition Factors The allometric condition factor (KA) was estimated using the equation of Tesch (1968): W/Lb, where W is the body weight (g) and L is the TL (cm), and b is the LWR parameter. The Fulton's condition factor (KF) was calculated using the equation of Fulton (1904): KF =100× (W/L3 ), where W is the body weight (g) and L is the TL in cm. The scaling factor of 100 was used to bring the KF close to unit. Moreover, the relative condition factor (KR) was calculated following the equation of Le Cren (1951): KR = W/(a×Lb ), where W is the body weight (g), L is the TL (cm) and a and b are LWRs parameter. For assessing the relative weight (WR), the equation of Froese (2006): WR = (W / Ws) × 100, were used, where W is the weight of a particular individual and Ws is the predicted standard weight for the same individual as calculated by Ws = a×Lb where the a and b values are gained from the relationships between TL vs. BW. 2.5. Form Factor (a3.0) The a3.0 of N. nandus was calculated according to the equation of Froese (2006) as: a3.0 = 10 logs as (b-3), where a and b are the regression parameters of LWRs and s is the regression slope of ln a vs. b. In the present study, a mean slope S = -1.358, was used for estimating the form factor because information on LWRs is not available for this species for estimation of the regression (S) of ln a vs. b. 2.6. Size at First Sexual Maturity (Lm) The Lm was calculated using the empirical equation, log (Lm) = -0.1189 + 0.9157 * log (Lmax), where Lmax is the maximum observed length (Binohlan and Froese, 2009). 2.7. Natural Mortality (MW) The MW of N. nandus was calculated using the model, MW =1.92 year-1 *(W)-0.25 (Peterson and Wroblewski, 1984), where, MW = Natural mortality at mass W; and W = a*Lb , a and b are the regression parameters of LWR. 2.8. Statistical Analysis For statistical analysis, GraphPad Prism 6.5 Software was used. The Spearman rank correlation test was applied to analyze the relationship of condition factors with TL, and BW. The one sample t-test was applied to compare the mean relative weight (WR) with 100 (Anderson and Neumann, 1996). All statistical analyses were considered significant at 5% (p<0.05).

Source of Information: Jordan Journal of Biological Sciences Volume 10, Number 1,March 2017, Pages 57 - 62 ISSN 1995-6673

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Achievement/Findings:

Our findings describe the population patterns of N. nandus including length-frequency distribution, growth pattern based on LWRs, size at sexual maturity, natural mortality, best-suited condition factor, relative weight and form factor. The results of the present study would be a valuable means for fishery managers, fish biologists and conservationists to begin early management policies and regulations for the sustainable conservation of the enduring stocks of this fish species in the Ganges River and neighboring ecosystem.

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