What is the ideal concentration of eugenol to anesthetize juvenile tilapia?

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By Milthon Lujan

Experiment Design. Source: da Paz et al., (2024); Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology.
Experiment Design. Source: da Paz et al., (2024); Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology.

Anesthetics have become an important tool for fish farmers as they play a crucial role in minimizing stress and mortality during essential management tasks such as transportation and pond maintenance.

A popular option among fish farmers is clove oil, with eugenol as the key ingredient. A study published by scientists from the Federal University of Pará and the Federal Institute of Education, Science, and Technology of Para (IFPA) delves into the effects of eugenol on Nile tilapia (Oreochromis niloticus), aiming to find the perfect anesthesia dose.


Eugenol is one of the main components of clove oil (Syzygium aromaticum); it represents between 90 to 95% of the oil and has been used in perfumes, flavorings, essential oils, as well as an antiseptic and local anesthetic.

It has also been reported that clove oil has an excellent protective effect on fish immunity and performance and can substitute antibiotics to combat pathogens (Saeed et al., 2022). It has the potential to combat saprolegnia in tilapia (Mostafa and Yassin, 2022).

Eugenol has demonstrated various antioxidant, analgesic, antimutagenic, antiplatelet, antiallergic, anti-inflammatory, and anti-inflammatory properties (Ulanowska and Olas, 2021); however, different scientific studies warn that the pharmacological effects of eugenol are complex and depend on the concentration of free eugenol used.

At high concentrations, this compound can be toxic.

Determination of the ideal concentration

The researchers tested 108 tilapia, exposing them to different concentrations of eugenol and monitoring their behavior and heartbeats. They analyzed five doses (50, 75, 100, 125, and 150 μL·L−1) to determine movement, reflexes, and recovery, while seven (including controls) underwent electrocardiograms to monitor their heart rate.

A safe zone emerges

In aquaculture, eugenol has been studied to treat parasite infections in fish such as cachama (Colossoma macropomum); during the transportation of angelfish (Pterophyllum scalare) and carp, and in the weighing of cachama fry.

At concentrations between 50 and 100 μL/L, tilapia became sedated, and their swimming, balance, and reflexes gradually faded. Best of all, they returned to their usual state, demonstrating that the effects are reversible.

But, scientists warn, if you exceed 100 μL/L, things get complicated. Eugenol began affecting tilapia hearts, causing changes that did not completely disappear within the study period. This raises concerns about possible long-term impacts on fish cardiovascular health.

Application in fish farming

Eugenol has been used by fish farmers; however, the study results provide a safety range in which this compound can be used for the transportation of Nile tilapia juveniles.

This way, tilapia farmers have a new tool to help reduce stress or improve the transport conditions of their fish.

Conclusion: Anesthesia with a dose of caution

This study paints a clear picture: to safely anesthetize juvenile tilapia, you should stay in the range of 50-100 μL/L. If a deeper sedation is needed, proceed with care and closely monitor your fish. Remember, their well-being is paramount!

This research opens doors for further exploration. Future studies could investigate the long-term effects of higher doses, test alternative anesthetics, and develop even more precise dosage guidelines for different sizes of tilapia and life stages.

Clarissa Araujo da Paz
Laboratory of Pharmacology and Toxicology of Natural Products, Biological Science Institute
Federal University of Pará, Brazil
Email: clarissa.paz@icb.ufpa.br

da Paz, C. A., da Costa, B. M. P. A., Hamoy, M. K. O., dos Santos, M. F., da Rocha, L. L., da Silva Deiga, Y., … & Hamoy, M. (2024). Establishing a safe anesthesia concentration window for Nile tilapia (Oreochromis niloticus)(Linnaeus 1758) by monitoring cardiac activity in eugenol immersion baths. Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology, 109839.

Other References

Mostafa, A. A. F., & Yassin, M. T. (2022). Efficiency of Syzygium aromaticum and Punica granatum extracts for the prevention of saprolegniasis on Oreochromis niloticus fish. Aquaculture Research, 53(10), 3654-3663.

Saeed, M., Khan, M. S., Younas, U., Siddique, F., Niaz, K., Farooq, Z., … & Ramadan, M. F. (2022). Clove (Syzygium aromaticum) and its derivatives in fish feed. In Clove (Syzygium Aromaticum) (pp. 257-266). Academic Press.

Ulanowska, Magdalena, and Beata Olas. 2021. “Biological Properties and Prospects for the Application of Eugenol—A Review” International Journal of Molecular Sciences 22, no. 7: 3671. https://doi.org/10.3390/ijms22073671

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