Objective  To investigate the correlation between morphological characteristics and body mass of red swamp crawfish (Procambarus clarkii) in the Yutai area of Shandong Province.

Methods  Through correlation analysis, path analysis, and decisive analysis. The study measured the body mass and 12 morphological traits of 195 tail P. clarkii (weighing≥15 g), and examined the impact of morphological traits on body mass. Additionally, the study established a regression equation for body mass using stepwise regression and constructed fit curves for individual traits and body mass.

Results  The results revealed that the coefficient of variation of body mass was highest across all populations, indicating that body mass had a greater selection potential compared to other traits. Moreover, morphological traits were significantly correlated with body mass in mature individuals (P<0.05 or P<0.01). Path analysis and decisive analysis further identified key traits influencing body mass within different populations. For females, total length, head breastplate width, pincers width, and telson length were primary factors, while for males, pincers width, head breastplate length, and head breastplate width were significant. In mixed populations, total length, pincers width, and head breastplate width played major roles. Regression equations for females, males, and mixed populations, with morphological traits as independent variables and body mass as the dependent variable, were derived as follows. Female population: y_female=−29.103+0.169X₂+1.018X₇+0.694X₅+0.561X₁₀ (R²=0.856); male population: y_male=−38.973+1.243X₅+0.209X₆+1.882X₇ (R²=0.918); mixed populations: y_mixed=−48.475+0.395X₂+1.368X₅+0.97X₇ (R²=0.932). The fit curve models for the main morphological traits and body mass of P. clarkii in Yutai area were mainly binomial models, otherwaise the fit curve model for head breastplate width and body mass in mixed populations was power function model, the fit curve model for pincers width and body mass in female population was the exponential function model. Curve model types in different populations were also different.

Conclusion In the breeding of P. clarkii in Yutai area, head breastplate width should be considered firstly, while pincers width and head breastplate length should be as assistant traits in the selection in male population. Head breastplate width should be considered firstly, while pincers width, total length and telson width should be as assistant traits in the selection in female population. Pincers width should be considered firstly, while total length and head breastplate width should be as assistant traits in the selection in mixed populations. Fit curve models predominantly followed binomial patterns for main morphological traits and body mass of P. clarkii in Yutai area.

Significance The results of this study may provide reference for the genetic breeding of P. clarkii.