The lesser spiny eel, Macrognathus aculeatus (Bloch, 1786), holds substantial economic importance as a food fish in South Asia, due to its exceptional nutritional value. This study was conducted to investigate the reproductive ecology of M. aculeatus within the Gajner beel wetland ecosystem in northwestern Bangladesh, with a specific focus on size at sexual maturity, spawning season, and fecundity in relation to eco-climatic variables. A total of 649 M. aculeatus female individuals were randomly collected from January to December 2018, with 440 mature selected for this study. The findings of this study revealed that the female's total length (TL) exhibited a range from 10.5 to 28.0 cm. Multiple methods, including maximum length (L