<p>Blue mackerel (<i>Scomber australasicus</i>) is an important fish species in the East China Sea. To better understand its replenishment patterns, we studied the fecundity of 60 female samples collected from March to April 2023–2024 in the South-Central region. The breeding stock included individuals aged 1⁺–8⁺, with potential fecundity ranging from 72,320 to 828,008 oocytes per fish (average: 176,400). Relative fecundity based on fork length varied from 231.79 to 2064.86 oocytes/mm (average: 538.15), and based on body mass from 194.40 to 1261.75 oocytes/g (average: 460.36). Oocyte size and individual fecundity increased with age, peaking at 7⁺&#xa0;years. Correlation analysis shows that both individual potential fecundity and fork length relative fecundity are not significantly correlated with fatness, while body weight relative fecundity is extremely significantly correlated with fatness. Multiple regression indicated ovarian weight was positively correlated with both potential and relative fecundity. The best-fit equation revealed that ovarian weight is the strongest predictor of fecundity. Consequently, management efforts should focus on protecting older mackerel, as they produce higher-quality oocytes despite their smaller population size.</p>