Population dynamics and stock assessment of the high-valued small indigenous fish mola (Amblypharyngodon mola) through length-based stock models in the River Chitra, Bangladesh

Abstract

The current study focused on the detailed data on stock assessments , including population structure, growth parameters, mortality, recruitment pattern, exploitation rate (E), maximum sustainable yield  (MSY) and relative yield per-recruit of the commercially important small indigenous fish, mola (Amblypharyngodon mola).  In total, 410 specimens of A. mola were collected through regular monthly intervals during January to December 2023, using the gill net from the Chitra River, located in the plain region of Narail district, Bangladesh. Total length (TL) and body weight (BW) of the collected A. mola specimens were measured using the digital slide callipers and electronic balance. The asymptotic length (L_∞) was estimated to be 8.9 cm, and growth coefficient (K) was 0.67 year⁻¹. The isometric value, b, was 3.133, which indicated the positive allometric growth. The growth performance index (Ø′) was estimated to be 4.02. The age at zero length (t₀) was 0.15 years and life-span (t_max) was found to be 4.22 years. The estimated total mortality (Z), natural mortality (M) and fishing mortality (F) were obtained to be 0.86, 1.03 and -0.19 year⁻¹, respectively. However, the negative fishing mortality indicated minimal fishing pressure on the stock of A. mola. The recruitment was observed throughout the year with two peak events during the months of July and October. Length at first capture (L_c) was 7.05 cm TL. The exploitation rate (E) was -0.19, where the E_max (exploitation rate producing maximum yield) was 0.42, suggesting under exploitation. The MSY of the A. mola stock was estimated at 1.01 mt. The results obtained from this study would be very useful to execute specific management for A. mola in the Chitra River. This study is the first investigation on population dynamics and stock status of the economically important A. mola fish in the Chitra River, the plain region of Narail, Bangladesh, the findings of which would be helpful towards the fisheries management and biodiversity conservation of this important fish species substantially.