Seasonal Variations of Growth Pattern and Condition of Paradise threadfin <i>Polynemus paradiseus </i> (Polynemidae) from Tetulia River in Southern Bangladesh

Abstract

A total of 900 individuals (pre-monsoon = 250, monsoon = 350, post-monsoon = 300) of <i>P. paradiseus</i> were collected from the fishers catches during January to December 2014. For each individual, TL (total length) and BW (body weight) were measured with 0.1 cm and 0.1 g accuracy, respectively. Length weight relationship (LWR) was estimated by the equation, <i>W </i> = <i>a </i> × <i>L^b</i>. Length-frequency distributions (LFD) were significantly different between the seasons (<i>P </i> &lt; 0.001). Allometric coefficient (<i>b</i> values) of LWRs (TL <i>vs.</i> BW) indicated isometric growth in pre-monsoon and post-monsoon (<i>b </i> ≈ 3), but negative allometric growth was found in monsoon (<i>b </i> &lt; 3). All LWRs were highly significant (<i>P </i> &lt; 0.001) with all <i>r²</i> values ≥ 0.984. The LWRs were significantly difference between the seasons (ANCOVA, <i>P </i>&lt; 0.001). The <i>K_F</i> is highly correlated with TL (Spearman rank test,<i> P </i> &lt; 0.001) in all the seasons, thus suggesting the best condition factor for assessing the wellbeing of this fish in our study area. Additionally, the <i>W_R</i> was significantly different from 100 (Wilcoxon rank test, <i>P </i> = 0.003) in pre-monsoon, which indicates the habitat was in poor condition for <i>P. paradiseus</i>, nevertheless it was not significantly differed in monsoon (<i>P </i>= 0.0186) and post-monsoon (<i>P </i> = 0.423). The calculated <i>L_m</i> was 12.1 cm in TL and form factor was 0.0061 for <i>P. paradiseus</i> in the Tetulia River.