Anesthetic Efficacy and Physiological Response to MS‐222, Eugenol, and Cymbopogon flexuosus Essential Oil in Juvenile Spotted Seatrout ( Cynoscion nebulosus )

For aquaculture, animal welfare constitutes a fundamental dimension of sustainability because it directly influences health, productivity, resource efficiency, and the ethical standards of production systems. Spotted seatrout ( Cynoscion nebulosus ) is a marine fish recognized as an emerging candidate for aquaculture in the Gulf of Mexico and, like other developing species, is continually subjected to experimental research to support the advancement of its culture technologies. In this context, identifying effective anesthesia conditions is essential for minimizing stress during operational procedures and improving the consistency of experimental outcomes. The aim of this study was to comparatively evaluate anesthetic effectiveness in juvenile spotted seatrout using behavioral responses and blood biochemical stress indicators. The anesthetic effectiveness of MS‐222, eugenol, and Cymbopogon flexuosus essential oil (CFEO) was evaluated in juvenile spotted seatrout (mean ± SD: 28.2 ± 3.5 g wet weight and 14.7 ± 0.7 cm total length). MS‐222 at 200, 250, and 300 mg L −1 , eugenol at 25, 30, 35, and 40 mg L −1 , and CFEO at 100 and 125 µL −1 induced deep anesthesia within 15 min, followed by complete recovery within 5 min. However, only MS‐222 at 300 mg L −1 and eugenol at 40 mg L −1 achieved deep anesthesia within 3 min, 110.0 and 149.5 s, respectively. Despite this, MS‐222 at 300 mg L −1 produced the highest plasma lactate levels, whereas eugenol at 40 mg L −1 elevated both plasma lactate and glucose relative to the control group. In contrast, eugenol at 35 mg L −1 resulted in the lowest plasma lactate and glucose levels. These findings indicate that eugenol at 35 mg L −1 represents a balanced anesthetic option for juvenile spotted seatrout. Moreover, rapid anesthetic induction does not necessarily imply reduced physiological stress in this species.