Anesthetics efficacy and physiological response of MS222 and clove oil in spotted knifejaw Oplegnathus punctatus

Anesthesia prevents mechanical injuries and manipulation stress during fish farming. The efficacy of the clove oil and tricaine methanesulfonate (MS222) and their effects on respiratory frequency, the proportion of the secondary lamellae available for gas exchange (PAGE), gill histological alteration, biochemical (cortisol, glucose, lactate, aspartate aminotransferase [AST], alanine aminotransferase [ALT]), hematological (white blood cells [WBC], red blood cells [RBC], hemoglobin [Hb], hematocrit [Hct]) and hepatic antioxidative parameters (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GSH-Px], malondialdehyde [MDA]) during anesthesia and recovery were determined to illustrate their underlying physiological response mechanisms in spotted knifejaw. Results showed that the anesthetic induction and recovery under clove oil (10, 20, 30, 35, 40 mg/L) and MS222 (50, 60, 70, 80, 90, 100 mg/L) treatment exhibited time-dose dependent manner for fish (206 g). The minimum concentrations of clove oil and MS222 producing desirable anesthetic properties were 35 mg/L and 80 mg/L, respectively. Rapid induction and recovery were observed in the fish with 16-839 g average body weight (BW) upon exposure to 35 mg/L clove oil and 80 mg/L MS222, while 30 min exposure cause the death of fish with 16 g average BW. The survival rate of the fish with the average BW of 102-839 g was more than 90 % after expose to 80 mg/L MS222 for 30 min. However, 35 mg/L clove oil treatment for 30 min induced significantly lower survival rate than 80 mg/L MS222. Meanwhile, 35 mg/L clove oil significantly increased PAGE, caused higher percentage of lamellar clubbing and hypertrophy compared with 80 mg/L MS222. Plasma glucose, lactate contents, AST and ALT activities, WBC and RBC counts, Hb and Hct levels exhibited similar results. These parameters recovered to nearly normal levels after the fish returned to normal active swimming for 6 h. Hepatic SOD, GSH-Px, and CAT activities and MDA levels were significantly stimulated by 35 mg/L clove oil but were not affected by 80 mg/L MS222 during anesthesia and recovery. These results suggest that compared with clove oil, MS222 exhibits advantages in different scenarios and its dose of 80 mg/L is recommended for use in spotted knifejaw.