Anesthetic effects of eugenol on adult ridgetail white prawn (Exopalaemon carinicauda) and its protective effects under simulated transportation

Anesthesia is a common practice used to improve animal welfare and reduce the negative impacts of stress factors in aquaculture settings. However, few studies have been conducted to investigate the application of anesthetics in ridgetail white prawn (Exopalaemon carinicauda). In the present study, the anesthetic efficacy and protective effects of eugenol in adults of this species were evaluated. When the prawns (n = 5) were immersed in different concentrations of eugenol in the range of 0–240 μl/L for 30 min, the results showed that 180 and 240 μl/L could lead to quick sedative and anesthesia effects with 100% mortality after 30 min exposure, while 30 μl/L failed to induce any sedative and anesthesia effects. Further tests showed that adult individuals were quickly anesthetized by eugenol at a concentration of 60–90 μl/L with a 30 min immersion, while half of the prawns were sedated in 30 μl/L eugenol after 4 h exposure, then recovered at 2 h without any mortality. Furthermore, we checked the water quality parameters after the adult prawns were immersed in four eugenol concentrations (0, 10, 20, 30 μl/L) for 8 h of simulated transportation followed by a 96 h recovery, we found that 30 μl/L eugenol treatment could significantly decrease the ammonia nitrogen concentration, and increased the survival rate at 96 h post recovery. The oxidative responses of the prawns during the 8 h transportation at 30 μl/L eugenol followed by 96 h recovery period were analyzed. The results showed that eugenol administration significantly decreased the malonaldehyde (MDA) concentration and the activities of most antioxidant-related enzymes immediately. The present data indicated that eugenol was an efficient anesthetic, which could be used for long-distance transportation of this species. It exhibited excellent protective effects to improve the animal's welfare by improving water quality and alleviating oxidative stress.