Comparative efficacy of tricaine methanesulfonate and clove oil for use as anesthetics in red pacu (Piaractus brachypomus)

To compare the anesthetic efficacy and physiologic changes associated with exposure to tricaine methanesulfonate and clove oil (100% eugenol). 15 adult cultured red pacu (Piaractus brachypomus). Fish were exposed to each of 6 anesthetic concentrations in a within-subjects complete crossover design. Stages of anesthesia and recovery were measured, and physiologic data were collected before and during anesthesia. Interval to induction was more rapid and recovery more prolonged in fish exposed to eugenol, compared with those exposed to tricaine methanesulfonate. The margin of safety for eugenol was narrow, because at the highest concentration, most fish required resuscitation. Mixed venous-arterial PO2 consistently decreased with anesthesia, while PCO2 consistently increased with anesthesia in all fish regardless of anesthetic agent. The increase in PCO2 was accompanied by a decrease in pH, presumably secondary to respiratory acidosis. Anesthesia was associated with increased blood glucose, potassium, and sodium concentrations as well as Hct and hemoglobin. Fish anesthetized with eugenol were more likely to react to a hypodermic needle puncture than fish anesthetized with tricaine methanesulfonate. Anesthesia induced with tricaine methanesulfonate or eugenol contributes to hypoxemia, hypercapnia, respiratory acidosis, and hyperglycemia in red pacu. Similar to tricaine methanesulfonate, eugenol appears to be an effective immobilization compound, but eugenol is characterized by more rapid induction, prolonged recovery, and a narrow margin of safety. Care must be taken when using high concentrations of eugenol for induction, because ventilatory failure may occur rapidly. In addition, analgesic properties of eugenol are unknown.