Spring Spawning in Oreochromis Mossambicus: Evidence from Monthly GSI, Maturity Stages, and Fecundity from Keenjhar Lake, Sindh, Pakistan

Abstract

Understanding the reproductive seasonality of Oreochromis mossambicus (Mozambique tilapia) is essential for aquaculture management and wild stock conservation. This study examined monthly variations in length?weight relationships (LWR), gonadosomatic index (GSI), maturity stages, fecundity, condition factor (K), and sex ratio of O. mossambicus collected from Keenjhar Lake, Sindh, Pakistan over 12 months (January–December 2023). A total of 244 individuals (120 females, 124 males) were analyzed. Female GSI peaked in March (4.8 ± 2.1%) and remained high through May, then declined sharply to <1% from July to October. Female condition factor (K) peaked pre-spawn in February (1.96) and reached a minimum in August (1.52), a decline associated with reproductive costs. The overall sex ratio (120 females: 124 males = 1:1.03) did not deviate from 1:1 (p=0.79). One?way ANOVA confirmed significant monthly differences in GSI for females (F (11,108) =12.34, p<0.001) but not for males (p=0.07). Fecundity ranged from 8 to 900 eggs, with a strong positive linear relationship with total length (cm): Eggs = 38.5 × Length (cm) – 565 (R²=0.68, p<0.001), valid for fish ?15 cm total length. Length?weight relationships showed negative allometric growth for females (b=2.89, ?<1) and isometric growth for males (b=2.95). Maturity stage V (ripe) dominated March–May, while stage VI (spent) prevailed July–September. A closed season during March–May is recommended to protect the spawning stock of this economically important cichlid in Keenjhar Lake.