Essential oil from Elionurus muticus as an anesthetic for Nile tilapia: Evidence of pH-dependent physiological responses

This study evaluated the anesthetic effect of essential oil from Elionurus muticus (EOEM) in Nile tilapia ( Oreochromis niloticus ) under different water pH conditions. Two experiments were conducted. In Experiment 1, fish (25 g) were exposed to EOEM concentrations ranging from 10 to 600 μL L −1 at pHs 5.5, 7.0, and 8.5 to determine induction and recovery times. In Experiment 2, fish (70 g) were transferred from water at pH 7.0 to waters at pHs 5.5, 7.0, or 8.5, anesthetized (600 μL L −1 ) or not, and sampled after 0 and 1 h for hematological and plasma biochemical analyses. The 600 μL L −1 concentration was efficient for anesthesia, with the shortest induction and recovery times at pH 7.0. Acidic and alkaline conditions prolonged recovery. In Experiment 2, after 1 h, unanesthetized fish at pH 5.5 exhibited elevated hemoglobin levels, while anesthetized fish at pH 8.5 had a reduced hematocrit. Leukocyte and heterophil counts were highest at pH 7.0, especially in anesthetized fish. Anesthesia at pH 7.0 reduced plasma total protein and albumin levels. Hyperglycemia was observed in unanesthetized fish at pHs 5.5 and 8.5. Plasma total cholesterol, high-density lipoprotein, and low-density lipoprotein levels were higher in the interaction between anesthesia and pH 8.5. Optimal performance occurred at pH 7.0, followed by pH 5,5, while pH 8.5 increased anesthetic recovery time and hematobiochemical stress.