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Length-weight Relationship and Condition Factor of Bombay Duck Harpadon Nehereus from Landings of Fishery Ghat, Chittagong

Tasnuba Hasin
Department of Fisheries Resources Management, Faculty of Fisheries, Chittagong Veterinary and Animal Sciences University, Chittagong-4225, Bangladesh

Abstract/ Executive Summary:

The current study describes the length-weight relationships and condition factor of Bombay duck, Harpadon nehereus from landings of Fishery Ghat, Chittagong. A total of 300 individuals caught by various mesh size of gill nets by commercial fishers were investigated from April 2016 to June 2016. On the basis of hypothetical cube law W=aLb, the variance of ‘b’ for both total length and standard length were estimated statistically (0.0090 and 0.0088 respectively). Using the value of t=1.96 at the 95% confidence limits for ‘b’ were estimated as 2.218 to 2.590 for total length-weight relationship and for standard length-weight relationship, 1.985 to 2.353 which indicated allometric growth pattern for both cases. The monthly relative condition factor during three months of observation (0.978, 1.033, and 1.097) showed no notable difference due to spawning strain, spent condition and lower feeding rate right after peak spawning season.

Keywords: Harpadon nehereus, Length-weight relationship, Condition factor, Allometric growth

Location: Fishery Ghat fish market, Firingi Bazar, Chittagong, Bangladesh

Start Date: 00-04-2016

End Date: 00-06-2016

Program Area: Animal Health and Management

Commodity: Duck

Objectives:

To identify the Length-weight Relationship and condition factor of Bombay Duck Harpadon nehereus from Landings of Fishery Ghat, Chittagong

Methodology:

The present study was conducted in Fishery Ghat fish market, Firingi Bazar, Chittagong, Bangladesh during April 2016 to June 2016 of which sampling was carried out at monthly interval. The samples were collected from different commercial gill-netters. They were transported to laboratory for length and weight data measurement. The total length (from the tip of the snout to the end of the caudal fin) and standard length (from the tip of the snout to the mid- of point caudal peduncle) of 300 fish were measured using a meter scale (1±mm) and weighed to the nearby ‘g’ using precision balance (0.001g). Total and standard length varied in the size range of 11.8 cm to 25.4 cm and 9.9 cm to 21.4 cm, correspondingly, and the weight ranged from 4.36 g to 52.71 g. Length-weight relationship: The length-weight relationship of Harpadon nehereus was estimated using the power curve equation, W= aL^b(King, 2007) where, W= Body weight (g) of the fish, L= Total length (cm) (TL) or standard length (cm) (SL) of fish and ‘a’ and ‘b’ are the constants. The value of ‘b’ is used to estimate the individual growth, in which hypothetically following a premise that b = 3 stands for isometric growth (the length growth in line with the increasing weight) whereas b > 3 indicates that the weight gain is faster than length (positive allometry) and oppositely b < 3 points to negative allometry. The above equation can be transformed into a linear form using natural logarithm as lnW = ln a + b ln L where Ln a and b equate to the intercept and slope. A power curve-of-best-fit for both total length and standard length is drawn through the points representing predicted weight for a range of arbitrarily chosen values for length wherein the value of ‘a’ and ‘b’ and the chosen value of L in the power equation were substituted. The non-linear and linear equations were fitted separately for total length (TL) and standard length (SL). The correlation coefficient (r) and variance of ‘b’ (Sb²) were calculated following standard statistical procedures. Using the value of ‘t’ from statistical table (King, 2007)with n-2 degrees of freedom the 95% confidence limits are estimated as b ± t× S_b. Relative condition factor (CFw): The relative condition factor (Kn) of H. nehereus was calculated using the formula CFw= /Wpred (King, 2007) based on total weight relationship, where CFw= relative condition factor; Wpred = predicted weight. Monthly values of mean weight are compared with predicted value for fish of the same mean length.

Source of Information: Res. Agric. Livest. Fish. Vol. 3, No. 2, August 2016: 355-360

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

In this study, the length-weight relationship of Harpadon nehereus samples collected from a local market was investigated over three months as part of an ongoing annual research. The findings indicate that the sample of Bombay duck individuals caught by the local gill netters followed an allometric growth pattern. The result of the study also implies that the lower values of relative condition factor was due to sampling immediately after peak spawning season which gradually changes with food availability, seasons and reproductive stages of the stock. During recent years a decreasing trend in Bombay duck fishery is being observed which might be a result of pollution, over exploitation, ineffective management and lack of information on growth in some cases. Studying population dynamics and growth parameters is necessary for proper stock assessment of a fishery where the ultimate goal is to maintain a sustainable yield in future. Present study would help to this extent. In addition further attention should be paid to for improved management of the stock.

Knowledge Management: Journal