Eugenol or MS-222 for anesthetising a fish several times over? What a study found
Published by Planète Pets · managing editor: Clément Lacaille · how our guides are written
A vet check, a sample, careful handling before a transport: briefly anesthetising a fish is sometimes necessary, and the choice of agent is not neutral when the procedure has to be repeated. A study by Ayala-Soldado, Mora-Medina, Molina-López, Lora-Benítez and Moyano-Salvago, published in August 2024 in the journal Animals, compared eugenol (clove oil) with MS-222, buffered or not, in zebrafish anesthetised on repeated occasions (, doi 10.3390/ani14162418). Our guidance on safe handling is gathered in the travel and safety section; see also our study on clove-oil sedation for betta transport.
Contents · 5 sections
Four anesthesia episodes, the same fish
The researchers exposed the same zebrafish to several anesthesia episodes spaced out over time, under four protocols: eugenol, unbuffered MS-222, and buffered MS-222 at two concentrations. They timed induction (time to reach deep anesthesia) and recovery, then observed swimming behaviour in the hours following each episode.
A trade-off between speed of induction and speed of recovery
Eugenol put the fish under faster than MS-222, but with a markedly longer recovery; swimming frequency also stayed reduced after eugenol anesthesia. Buffered MS-222, by contrast, proved more effective and more consistent than its unbuffered form. The authors' conclusion: for brief, repeated anesthesia, such as successive check-ups, buffered MS-222 is the more reliable choice.
What this study does not show
It covers zebrafish, a small species used in the lab; induction and recovery times may differ noticeably in larger aquarium species or ones with a different anatomy (labyrinth fish, flatfish). It also does not measure cortisol or other physiological stress markers, only timings and observed swimming behaviour.
What this means in practice
For anyone who needs to handle a fish repeatedly over a short period — veterinary treatment, repeated transfers, taking measurements — the trade-off between speed of induction and speed of recovery is worth weighing case by case rather than defaulting to whichever product is most common at the pet shop. Buffering MS-222 (with sodium bicarbonate, to neutralise its acidity) is not an optional detail: the study shows it clearly outperforms the unbuffered form.
Frequently asked questions
Can eugenol be used for a fish handled only once?
This study covers repeated anesthesia; for a one-off use, the trade-off between induction speed and recovery time still applies but matters less.
Is MS-222 freely available to a home aquarist?
Its availability varies by country and is often restricted to veterinary use; clove oil remains the most accessible option for occasional home use. Find all our guides on the fishkeeping hub.
See it in the Planète Pets shop: Mini USB aquarium air pump with tubing and air stone (€22.90) · the whole shop
This guide is part of Planète Pets’s Fishkeeping universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.