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Length-weight Relationship and Population Dynamics Study of the Giant Catfish (arius Thalassinus) in the Bay of Bengal Coast of Bangladesh

Rokeya Sultana
Chattogram Government College, Chattogram, Bangladesh

Mohammed Shahidul Alam
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong-4331, Bangladesh

K. M. Shahriar Nazrul
Department of Fisheries, Ministry of Fisheries and Livestock, Bangladesh

Al Mamun
Marine Fisheries Survey Management Unit, Department of Fisheries, Bangladesh

Md. Abdullah Al-Mamun
Department of Fisheries, Ministry of Fisheries and Livestock, Bangladesh

Abstract/ Executive Summary:

The present study investigated the length-weight relationship, population parameters and the instantaneous natural mortality rate of Arius thalassinus from two major landing center of Bangladesh using the FAO-ICLARM Stock Assessment Tools (FiSAT II). A total of 1789 specimens were collected between January 2016 and December 2017. The estimated values of the exponent “b” was ranged from 3.019 (pre-monsoon) to 3.293 (monsoon), indicating an isometric growth pattern of the species with high correlation coefficients (0.904 to 0.927). The equation of length–weight relationship was: W=0.005L^3.181. Model parameters of the von Bertalanffy growth equation were: L∞ = 97.60 cm and K = 0.33^-1 year. The estimated growth performance index (Ø) was 3.497. The instantaneous natural mortality rate (M) was 0.62^-1 year and a high exploitation rate (E) 0.62 (>0.50) showed that this fish is over-exploited in the Bay of Bengal coast of Bangladesh.

Keywords: Length-Weight, Relationship, Arius thalassinus, Bay of Bengal

Location: BFDC ghat, Cox’s Bazar and Fishery Ghat, Chittagong

Start Date: 00-01-2016

End Date: 00-12-2017

Program Area: Resource Development and Management

Commodity: Cat fish

Objectives:

To establish the key population parameters of Arius thalassinus by presenting the Length-Weight Relationship, estimating the growth parameters (L∞, K & to) and calculating the instantaneous natural mortality rate.

Methodology:

A total of 1791 samples of Arius thalassinus was collected from the commercial catches landed at two major landing centers in Bangladesh i.e. BFDC ghat, Cox’s Bazar (21⁰ 27' 4.04" N and 91⁰ 58' 16.62" E) and Fishery Ghat, Chittagong (22⁰ 19' 38.33" N and 91⁰ 50' 50.15" E) between January 2016 and December 2017. Length-frequency data were obtained at the landing sites. Fishes were randomly selected and measured the total length (±0. 1 cm) and weighed (±0. 01 g) using a metric scale. The LWRs for different seasons were calculated by applying the exponential regression given by Le Cren (1951): W = aL^b; Where, W is body weight (g), L is the total length (cm), a is a coefficient related to body form, and b is an exponent indicating the isometric growth of fish when b = 3 (Beverton and Holt 1996; Froese 2006). The length-frequency data was grouped into 5 cm class intervals for the estimation of growth parameters. The two years data were pooled for one year by using FAO-ICLARM Stock Assessment Tools (FiSAT II) (Pauly & David 1981). The ELEFAN I procedure in FiSAT II was employed to estimate growth parameters (L∞ and K) of the von Bertalanffy growth function (VBGF): Lt= L∞ [1 - exp-K(t- t0)], Where, Lt is the length at age t, L∞ is asymptotic length, K is the growth coefficient, and t0 is the theoretical age of fish at zero length t0 was estimated from the “Analysis of Length-at-Age data” routines. The growth performance index (Ø) for Arius thalassinus was calculated according to the following formula (Pauly and Munro 1984): = log K + 2 log L∞ The total instantaneous mortality (Z) was estimated by length converted catch curve method (Pauly 1983). Estimation of natural mortality rate (M) was carried out using the following empirical equation proposed by Pauly (1980): Log M = -0.0066 – 0.279 log L∞ + 0.6543 log K + 0.4634 log T; Where, M is natural mortality and T is the mean annual sea surface temperature, which was taken as 28.20C during the sampling period. Annual instantaneous fishing mortality (F) was calculated by subtracting the natural mortality rate (M) from the total mortality (Z) (F = Z-M). Present exploitation rate (E) was analyzed as the proportion of the fishing mortality (F) relative to total mortality (E = F/Z) (Gulland 1971).

Source of Information: Res. Agric., Livest. Fish.6(3): 439-444, December 2019

Article Link (Online Journal): DOI: https://doi.org/10.3329/ralf.v6i3.44810

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Finally, this was the first report on the growth parameters of the species in the Bay of Bengal coast of Bangladesh which provides basic biological information that will be useful for the assessment and management of Arius thalassinus fishery in this region.

Knowledge Management: Journal