In Senegal, studies on the family Mugilidae are rare and little data is available on their reproductive biology. This study, carried out in the MPA of Niamone–Kalounayes (Casamance River estuary, Senegal) aims to enhance our knowledge of the reproductive biology of the largescale mullet, Parachelon grandisquamis (Valenciennes, 1836), a species highly prized by the local population as a food source. To better understand its reproductive biology, a series of monthly samplings over twelve (12) months from July 2021 to June 2022 was carried out. Experimental fisheries were carried out at six (6) stations located in secondary channels lined with mangroves, using a seine net (250 m long and 25 mm mesh side). A total of 361 individuals were sampled, including 321 female specimens and 40 male specimens. The calculated sex ratio was in favor of females (1:8), with a significant difference between the calculated sex ratio and the theoretical 1:1 sex ratio (χ2 = 218.73; P-value < 0.05). In the MPA of Niamone–Kalounayes, the breeding period of P. grandisquamis extends from March to July, from the end of the dry season up to the beginning of the wet season. The sizes at first sexual maturity were 17 cm in males and 18 cm in females, showing that in the MPA of Niamone–Kalounayes, males and females of P. grandisquamis reach sexual maturity at very close sizes (χ2 = 0.02; P > 0.05). As this species is subject to the intense fishery by many actors in the area, these findings may be proven useful in the process of developing a management plan for this particular species.