Caudal peduncle depth and total length as reliable predictors of body weight in Sarcocheilichthys sciistius : A multi-method morphometric approach

Reliable body weight estimation is essential for conservation-relevant field monitoring and captive breeding, but direct measurements of small fishes are often constrained by handling stress, escape behavior, and limited field equipment. We applied a multi-method morphometric approach combining grey relational analysis (GRA), path analysis, allometric scaling, curve fitting, and size-stratified ontogenetic analysis to identify morphometric predictors of body weight in thicklip gudgeon, ( Sarcocheilichthys sciistius ), a small cyprinid distributed in northern China. Using 104 wild-caught specimens from the upper Huaihe River, we found that all nine measured traits were significantly correlated with body weight (p < 0.01). After correcting for multicollinearity, path analysis identified caudal peduncle depth (CPD) as the largest direct path coefficient (path coefficient = 0.519), ahead of total length (TL; path coefficient = 0.396). The optimal predictive model was BW = -12.543 + 12.156 × CPD + 1.159 × TL (R² = 0.812, p < 0.001). Allometric and size-stratified analyses showed axial traits (TL) grew isometrically, while CPD maintained high predictive stability across ontogenetic stages despite its negative allometry. Cephalic traits showed weaker associations with body weight in larger individuals. Curve fitting showed that the quadratic model had the highest R² for CPD and the exponential model had the highest R² for TL, whereas power models provided biologically interpretable near-best fits consistent with allometric scaling. This approach may support field monitoring of S. sciistius and warrants validation in other small freshwater fishes.