Optimizing clove oil anesthesia in Silurus glanis: A welfare-oriented protocol validated across life stages for resource-limited aquaculture settings

Clove oil is a promising natural alternative to synthetic anesthetics in aquaculture, but species- and life-stage-specific validation is essential. This study evaluated clove oil (40–120 ppm) in fingerlings (30–95 g) and adults (950–1100 g) of Silurus glanis using a standardized seven-stage behavioral scale. Physiological biomarkers (cortisol, lactate, ALT, AST) were measured in adults at baseline and 24 h post-recovery. Deep anesthesia (Stage 7) was not achieved at 40 ppm. The optimal concentration was 80 ppm, providing rapid induction (1.83 min in fingerlings; 2.27 min in adults) and moderate recovery (4.25 and 5.42 min), with only a transient 1.6-fold cortisol increase and no significant changes in other biomarkers. In contrast, 120 ppm induced significant elevations in all biomarkers, indicating acute stress. Structural equation modeling confirmed a stress-mediated pathway linking higher clove oil doses to prolonged recovery. Thus, 80 ppm offers a safe, effective, and practical anesthetic protocol for both life stages.