Anesthetic effects of clove oil during handling and transportation of the freshwater prawn, Macrobrachium rosenbergii (de man)

Abstract

The present work was conducted to determine the effects of clove oil as an anesthetic on post- larvae (mean length 13.42±0.84 mm) and juveniles (43.57±0.94 mm) of the giant freshwater prawn, Macrobrachium rosenbergii. In the first of three experiments, exposure to ethanol for 15 min was ineffective in tranquilizing the freshwater prawns at concentrations of 75-625 mg/l for postlarvae and 375-5,000 mg/l for juveniles, indicating that ethanol could be used as a solvent for clove oil without contributing to any anesthetic reaction. In the second experiment, prawns were exposed to one of six clove oil concentrations for 15 min (15-125 mg/l for postlarvae; 75- 1,000 mg/l for juveniles). For postlarvae, the fastest induction (0.90±0.05 min) was achieved at the highest concentration (125 mg/l) but all prawns in this treatment died. Induction and recov- ery times in concentrations of 30, 45, and 60 mg/l were all under 15 min. At 75 mg/l, postlarvae were tranquilized in a relatively short period (3.30±0.10 min) and recovery time was maximum (45.17±0.20 min). For juvenile prawns, concentrations of 750 mg/l and up were fatal while 125 and 250 mg/l induced anesthesia in 78.30±0.20 and 66.83±0.18 min, respectively, with recovery in 4.21±0.12 and 16.91±0.16 min. As far as induction and recovery times are concerned, clove oil was a suitable anesthetic only for postlarvae. The third experiment revealed that a concen- tration of 15 mg/l could safely be used to transport postlarvae up to three hours.