Objective This study aims to elucidate the reproductive patterns of Procambarus clarkii in the Nanning region of Guangxi and assess the genetic diversity of new strains obtained through mass selection breeding, thereby providing a scientific basis for improved variety selection and seed production.

Methods Monthly dynamic sampling over 12 months was conducted at the Runshuang P. clarkii breeding base in Datang Town, Liangqing District, Nanning City. Gonadosomatic indices of male and female P. clarkii and berried cycle characteristics of females were systematically analyzed. Genetic diversity of three novel selective breeding lines (Egyptian, Yueyang-Hunan, and Qianjiang-Hubei populations) was evaluated using microsatellite markers.

Results The results showed that in spring, most female shrimp just began to develop, with a low gonadal index. After that, it gradually increased every month. The mature stage was from October to November, with the maximum value in October, and the ovarian index reached (3.45±0.12) %. The gonadal index of male shrimp also reached its maximum value in September and October, at 0.11% and 0.10% respectively. The gonadal development of both male and female individuals was basically synchronous. The new strains of P. clarkii obtained through mass selection and breeding for three generations all have relatively rich genetic diversity (expected heterozygosity, 0.743<H_e<0.779; polymorphism information content, 0.708<PIC<0.751), exceeding pre-breeding levels (F₀). The Egyptian population (H_e was 0.779, PIC was 0.751) exhibited relatively high genetic diversity.

Conclusion Synchronized gonadal maturation peaks in October, and the new strain obtained through mass selection exhibites high genetic diversity. These findings provide critical data and theoretical support for P. clarkii genetic improvement and large-scale seedling production.