Essential oils as natural anesthetics for Nile tilapia

In modern aquaculture, the constant handling of fish is an operational necessity. Activities such as biometry, transport, and vaccination are essential to ensure productivity, but they also represent significant sources of stress for the animals. To mitigate this impact, the use of anesthetics has become indispensable. Nevertheless, there is a growing interest in replacing synthetic agents with natural solutions that are safe for the fish, the operator, and the environment.

Essential oils (EOs) have emerged as one of the most promising alternatives. These complex mixtures of volatile substances extracted from plants possess sedative and anesthetic properties that act directly on the central nervous system of fish.

The research was conducted on Nile tilapia (Oreochromis niloticus) by specialists from the Post-Graduation Program in Animal Husbandry, the Department of Industrial Pharmacy, and the Department of Physiology and Pharmacology of the Federal University of Santa Maria (UFSM), in Brazil. The original article was published in the scientific journal Fishes by MDPI.

Key Conclusions of the Study

• Proven Efficacy: Oils rich in compounds such as linalool, carvacrol, and pulegone induce deep anesthesia in less than 3 minutes.
• Rapid Recovery: Most evaluated essential oils allow the tilapia to regain equilibrium in less than 10 minutes, meeting operational standards.
• Oregano as a Leader: Origanum vulgare essential oil proved to be the most efficient, requiring the lowest concentrations for rapid induction.
• Physiological Responses: Although natural, some oils may induce initial stress responses (e.g., increased glucose), which generally stabilize following recovery.

Methodology: Scientific Rigor in Selection

To provide reliable data, researchers conducted a systematic review following PRISMA guidelines. From a total of 355 initial records in databases such as Scopus and Web of Science, 9 high-quality studies were selected that met strict criteria, such as the use of immersion induction and the presentation of quantitative data on induction and recovery times. Additionally, the risk of bias was assessed using the ARRIVE 2.0 checklist, ensuring that the analyzed experiments were methodologically sound.

Stages of Anesthesia in Tilapia

To standardize the results, the study adapted the evaluation criteria into four fundamental stages:

1. Light Sedation (I): Decreased reactivity to visual stimuli; slightly reduced opercular activity.
2. Deep Sedation (II): Partial loss of equilibrium and tactile response only to strong pressure on the caudal fin.
3. Light Anesthesia (III): Total loss of equilibrium; the fish turns over and locomotion ceases.
4. Deep Anesthesia (IV): Total loss of reflex activity and minimum opercular rate.

Results: The Most Effective Oils and Their Compounds

The research highlights that the effectiveness of an essential oil depends directly on its predominant chemical composition.

Key Compounds and Their Action

• Carvacrol: Found extensively in oregano oil (Origanum vulgare), it acts by inhibiting sodium currents in neurons, facilitating rapid anesthesia.
• Linalool: Abundant in basil (Ocimum basilicum) and in Lippia alba, this compound inhibits glutamatergic transmission.
• Eugenol: The main component of clove oil (Syzygium aromaticum) and Ocimum gratissimum, known for its effectiveness at low concentrations, although it may alter the flavor of the fillet if not handled properly.

Comparison of Induction Times

At a concentration of 50 uL/L, only Ocimum basilicum (methyl-chavicol chemotype) and Origanum vulgare oils managed to induce deep anesthesia in less than 3 minutes. Conversely, oils such as Nectandra grandiflora showed the lowest efficacy, requiring significantly longer times and higher concentrations.

Physiological Parameters and Stress

One of the most critical findings is how these compounds affect fish physiology. An ideal anesthetic should not only immobilize the animal but also minimize the stress response.

• Glucose and Cortisol: Oregano oil caused an initial increase in cortisol and glucose during anesthesia, but cortisol levels fell below control values after recovery, suggesting a long-term stress-mitigating effect.
• Lactate: In the case of Aloysia citriodora, an increase in plasma lactate levels was observed, which returned to normal after recovery.
• Welfare: Oils such as A. citriodora and L. alba (linalool chemotype) proved capable of reducing plasma cortisol levels, positioning themselves as excellent options for improving welfare during handling.

Challenges and Recommendations for the Producer

Despite the potential, the use of essential oils faces challenges. The chemical composition of plants can vary according to the season, collection site, and cultivation system. This means that the producer must be cautious and, if possible, use standardized products. Additionally, excessive concentrations or prolonged exposure can cause severe tissue hypoxia and even death. Therefore, it is recommended to follow the golden rule: induction in less than 3 minutes and recovery in less than 10 minutes.

General Conclusion of the Study

Essential oils represent a safe, sustainable, and effective alternative for the sedation and anesthesia of juvenile Nile tilapia. Origanum vulgare oil stands out for its potency, while others such as Lippia alba and Ocimum basilicum offer a balance between efficacy and reduction of physiological stress. These findings provide a solid basis for aquaculture professionals to make informed decisions that improve both operational efficiency and animal welfare.

The study was supported by the National Council for Scientific and Technological Development (CNPq, Brazil) and the Coordination for the Improvement of Higher Education Personnel (CAPES, Brazil).

Reference (open access)
Visoni, B. M., de Melo, T. P., Descovi, S. N., Heinzmann, B. M., & Baldisserotto, B. (2026). Essential Oils and Their Use as Anesthetics and Sedatives for Nile tilapia (Oreochromis niloticus): A Systematic Review. Fishes, 11(1), 19. https://doi.org/10.3390/fishes11010019

Milthon Lujan

Editor at the digital magazine AquaHoy. He holds a degree in Aquaculture Biology from the National University of Santa (UNS) and a Master’s degree in Science and Innovation Management from the Polytechnic University of Valencia, with postgraduate diplomas in Business Innovation and Innovation Management. He possesses extensive experience in the aquaculture and fisheries sector, having led the Fisheries Innovation Unit of the National Program for Innovation in Fisheries and Aquaculture (PNIPA). He has served as a senior consultant in technology watch, an innovation project formulator and advisor, and a lecturer at UNS. He is a member of the Peruvian College of Biologists and was recognized by the World Aquaculture Society (WAS) in 2016 for his contribution to aquaculture.