To evaluate the effects of different concentrations and exposure time of clove (Eugenia caryophyllata) oil on the anesthesia and recovery stages of Persian sturgeon (Acipenser persicus) fingerlings, three weight groups including 1.89 g (5-7 cm), 3.33 g (7-9 cm) and 4.25 g (9-11 cm) were studied via immersion method during short-term (5 min) and long-term (6, 10, 20 and 30 min) exposure to the anesthetic solution. Results showed that with an increase in clove oil concentration, the anesthesia stages happened more rapidly and the recovery stages happened more slowly (P<0.05). The mean time to achieve anesthesia and recovery stages during the short-term exposure for all weight groups ranged between 0.63-8.90 and 3.70-17.43 min, respectively. The Mean range of recovery stages for long-term exposure with an increase in clove oil concentration from 20 to 80 mg/L (14.7 to 58.8 mg/L eugenol), were 7.26-39.53 min. The significantly (P<0.05) lowest lethal time (MLT50) was 120 mg/L (88.2 mg/L eugenol in 20.33 min) for weight group 4.25 g/fish. The present study showed the high potential of clove oil for anesthetization of Persian sturgeon fingerlings. The recommended maximum clove oil concentration for induction time (stage 3) during the short time anesthesia is equal to 100 mg/L (73.5 mg/L eugenol) for all weight groups with 9-14 min time for stage III of recovery.

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