ON DRUGS: THE SEDATIVE EFFECTS OF CLOVE OIL ON POST-METAMORPHOSE JUVENILE CLOWNFISH Amphiprion ocellaris
Handling fish for the purposes of experimental measurement (e.g., length; weight) can cause death (at worst) or interruption of behavior and activity during the experimental process (at best). Clove oil is a natural substance that can be used to anesthetize (or euthanize) fish. It is relatively inexpensive and is generally regarded as safe for the user and fish. We investigated doses of clove oil (2.5, 5, 10, 15, and 20 ppm) to successfully anesthetize (but not euthanize) juvenile Ocellaris clownfish Amphiprion ocellaris (16−43 mm; 0.1−1.75 g).
Fish were immersed in their respective dosage in 500 ml clear plastic containers (13 x 12 x 7 cm). Fish immersed in 20 ppm immediately showed signs of stress within the first 20 seconds of being immersed. The fish then calmed after 30 seconds, became lethargic and showed loss of equilibrium between 45 seconds and one minute. The 15 ppm treatment did not exhibit the same stress as the 20 ppm treatment. After one minute in the 15 ppm treatment, the fish's respiration slowed and between 1.5 and 2 minutes, satisfactory anesthesia was achieved. The 10 ppm treatment affected the clownfish similarly, only requiring an additional 30 seconds until anesthesia was achieved. The fish exposed to the 5 ppm treatment showed no stress and seemed to exhibit subdued behavior within seconds of immersion. Satisfactory anesthesia was reached at 4 minutes in the 5 ppm treatment. The 2.5 ppm treatment was of little effect on the fish. After 5 minutes was reached in the 2.5 ppm treatment, the fish was transferred to the 15 ppm treatment to properly anesthetize the specimens for subsequent measurements. It is noteworthy that the 2.5 ppm treatment could provide some use as an intermediary level of anesthetic in situations when full anesthesia is not necessary or preferred.
Once anesthesia was achieved, each specimen was handled while data was collected for a length - weight relationship study. Most fish remained still while data was collected. When the procedure was completed, the specimens were returned to a recovery tank where behavior observations of lasting effects were monitored. Within one minute, fish placed in the recovery tank regained equilibrium and normal respiration. No fatalities or lasting interruptions of behavior were observed.