Assessing reproductive biology of Macrobrachium lamarrei in the Ganges River (NW Bangladesh) in relation to environmental parameters

Macrobrachium lamarrei (H. Milne-Edwards, 1837) is a well-known freshwater prawn species of Bangladesh. The aim of the research is to explore various reproductive aspects (size at sexual maturity, reproductive period and fecundity) of M. lamarrei in the Ganges River, Bangladesh through October 2012 to September 2013. We also study the environmental parameters and their impact on reproduction of M. lamarrei. A total 391 (ovigerous = 141, non-ovigerous = 250) female specimens were collected using Drag net. The TL(50) (the TL at which 50% of individuals become mature) was calculated by a logistic equation as 5.20 cm. Based on the availability of ovigerous females the spawning season was February-November with the peak June-July. Further, 50% and 90% ovigerous females were observed when Fulton’s condition factor (K(F)) was 0.85 and 1.03, respectively. The total fecundity (F(T)) was ranged from 65 to 370 where TL was 4.20–6.40 cm and BW was 0.84–2.50 g. Fecundity was found to be highly correlated with TL (r(2) ≥ 0.96, r(s) = 0.96, p < 0.0001) and BW (r(2) ≥ 0.88, r(s) = 0.93, p < 0.0001). Temperature (r(p) = 0.82, p = 0.009), dissolved oxygen (DO) (r(p) = −0.83, p = 0.0007), pH (r(p) = 0.80, p = 0.0014) and total alkalinity (r(p) = −0.87, p = 0.0002), were highly correlated with ovigerous females. The average temperature on peak spawning season was 32 °C. Also, the spawning period connected with the peak rainfall and showed a notable relation between rainfall and ovigerous females. In addition, exploration of long data series pointed that yearly average air temperature is rising by 0.029 °C yr(−1), whereas yearly average rainfall is falling by 2.96 mm yr(−1). Therefore, the result will be helpful for the sustainable management and conservation of M. lamarrei through fixed permissible mesh size and establishment of a ban period in the Ganges River, Bangladesh and adjoining ecosystems.