Biometry, sexual maturity, natural mortality and fecundity of endangered halfbeak Dermogenys pusilla (Zenarchopteridae) from the Ganges River in northwestern Bangladesh

Abstract

The present study express the biometry, including length-weight relationships (LWRs) using 12 equations, length-length relationships (LLRs) using 15 equations, condition factors (allometric, <em>K_A</em>; Fultonʹs, <em>K_F</em>; relative, <em>K_R</em>; and relative weight, <em>W_R</em>), form factor (<em>a_3.0</em>), first sexual maturity (<em>L_m</em>), natural mortality (M_W) and fecundity (<em>F_T</em>) of <em>Dermogenys pusilla</em> from the Ganges River, northwestern Bangladesh. A sum of 75 individuals was hardly collected using cast net and gill net during July 2013 to June 2014. In our study total length ranged from 6.6–16.1 cm for male and 7.5-15.6 cm for female and fin formula was- dorsal, D. 12 (4/8); pectoral, P₁. 11 (2/9); pelvic, P₂. 6 (1/5); anal, A. 13-14 (2-3/11-12) and caudal C. 18-20 (4/14-16). All LWRs were highly significant (<em>P</em> < 0.001) and based on highest value of <em>r²</em>, BW <em>vs.</em> FL was the best fitted model among 12 equations for both sexes. The analysis of covariance (ANCOVA) revealed significant differences between males and females for LWRs (<em>P</em> < 0.001). Also, all LLRs were highly correlated (<em>P</em> < 0.001) with <em>r²</em> values ≥ 0.940. According to highest value of <em>r²</em>, LLR by TL <em>vs.</em> FL was the best suited model among 15 equations for both genders. Based on Pearson correlation values, <em>K_F</em> was highly correlated with BW and TL; thus <em>K_F</em> can be used for the wellbeing of this species in the Ganges River. The <em>a_3.0</em> was 0.0025 for male and 0.0024 for female. The <em>L_m</em> was 9.70 cm TL for male and 9.40 cm TL for female. Also, the M_W was 1.13, 1.41 year^-1 for males and females respectively, and the fecundity was ranged from 620-1544 (mean ± SD = 1125 ± 248). Therefore, the findings of this study would be very effective for sustainable conservation of this endangered species in the Ganges River and surrounding ecosystem.