Changes in secondary sexual characteristics of female red swamp crayfish (Procambarus clarkii) and relationship to ovarian development: Implications for intensive breeding of seedlings

A rapid selection method of mature Procambarus clarkii females for use in intensive breeding of seedlings is proposed based on evaluation of secondary sexual characteristics and variation patterns in this study. Following regular sampling in ponds, the weight, cephalothorax length, annulus ventralis length, body width, white patch coverage (WC) on the uropod, and uropod content weight-to-weight (WW) ratio of female P. clarkii were found to change significantly during ovarian development. The random forest model identified white patches on the uropod as secondary sexual characteristics of female P. clarkii. In fact, the ovarian maturity status could be determined based on the variable pattern of these white patches (distribution shape, coverage, and density), particularly WC. White patches waxed and waned during ovarian development and oviposition. Specifically, white patches were absent from the uropod of female P. clarkii before the avitellogenic stage; visible on the uropod in the early vitellogenic stage (WC < 30%); WC 30–45% occurred in the midvitellogenic stage; WC > 45% occurred in the late vitellogenic stage; and white patches disappeared from the uropod of female P. clarkii in the post-vitellogenic and resorptive stage. The accuracy of identifying mature female P. clarkii (late vitellogenic stage) based on the white patch pattern was 86.36%. Hence, the observation of white patch changes on the uropod might represent an effective method for rapidly identifying mature female P. clarkii with the potential to improve artificial intensive breeding.