Anesthetic potential of Cinnamomum zeylanicum essential oil in Nile Tilapia (Oreochromis niloticus)

Abstract

This study aimed to determine the best anesthetic concentration of Cinnamomum zeylanicum essential oil (CZEO), and investigate its effects on physiological and histological parameters in Oreochromis niloticus. The animals were divided into two experiments: Experiment I: 100 fish (38.37 ± 9.28 g – 10 per concentration) were subjected to nine concentrations of CZEO (60, 70, 80, 90, 100, 110, 120, 130 and 140 μL L⁻¹) and control (95% ethyl alcohol) to determine the ideal concentration; and Experiment II: To evaluate the physiological and tissue effects of CZEO, 27 fish (86.69 ± 30.37 g) were allocated to three treatments: Control: fish were not exposed to the anesthetic; blood was collected, and they were euthanized. T0: fish were anesthetized with CZEO (100 μL L⁻¹); immediately after reaching anesthesia, blood was collected, and they were euthanized. T1: fish were anesthetized with CZEO (100 μL L⁻¹), returned to the tank for recovery, and one hour later, were re-anesthetized; blood was then collected, and they were euthanized. For all treatments, after euthanasia, samples of gill and liver tissues were collected. Blood and tissue samples were processed for physiological and histopathological analyses. The results showed that the 100 μL L⁻¹ concentration of CZEO is the most effective, keeping the hematimetric indicators stable, reducing the main stress indicators, and preventing injuries to the gills and liver. However, this concentration also resulted in an increase in lactate and congestion in the gill tissue. In addition, the continuous use of CZEO can lead to a rise in liver enzymes, although without significant histopathological changes. These findings indicate that while CZEO (100 μL L⁻¹) is a promising alternative for anesthesia in aquaculture, its use should be monitored to avoid adverse effects on fish health.