MS-222 (Tricaine) Fish Anesthetic: Dosing, Buffering and Safety
How MS-222 (tricaine methanesulfonate), the FDA-approved fish anesthetic, is dosed for sedation and anesthesia, why it must be buffered, and its 21-day food-fish withdrawal.
Overview
MS-222, tricaine methanesulfonate (also called tricaine mesilate, ethyl 3-aminobenzoate methanesulfonate), is a benzocaine-derived anesthetic supplied as a white powder. It is used to sedate, anesthetize and humanely euthanize fish and other aquatic cold-blooded animals during handling, sampling, surgery and transport. It is the only anesthetic approved by the FDA for use in fish destined for human food in the United States.
Mechanism of action
MS-222 acts as a local-type anesthetic by blocking voltage-gated sodium channels, preventing sodium ions from entering nerve cells and so blocking the transmission of action potentials. The drug is absorbed across the gills, which is why it is given by immersion in the water rather than by injection.
Administration and dosing
MS-222 is given by immersion. Effective concentrations vary with species, size, water temperature and the depth of anesthesia required, so a small group should be tested first. Reported anesthetic concentrations in the literature span roughly 25 to 400 ppm (mg/L); higher concentrations within this range are used for surgical anesthesia. For example, a peer-reviewed study found that 200 mg/L reliably produced a surgical plane of anesthesia in bluegill, reached in a median of about 109 seconds.
| Goal | Typical immersion concentration | Notes |
|---|---|---|
| Anesthetic range (literature) | about 25 to 400 mg/L (ppm) | Varies by species, size, temperature |
| Surgical anesthesia example (peer-reviewed) | 200 mg/L (bluegill) | Surgical plane reached in about 109 s |
| Recovery | Move to clean, well-aerated, drug-free water | Watch opercular (gill) movement |
During induction and recovery, monitor opercular (gill) movement and the righting reflex: a fish at a surgical plane loses equilibrium and shows slow, regular gill movement, and it should be moved to clean, aerated water to recover as soon as the procedure ends.
Buffering is required
Regulatory status and withdrawal
In the United States MS-222 is FDA-approved for the temporary immobilization of fish, amphibians and other aquatic cold-blooded animals. For food fish in the families Ictaluridae, Salmonidae, Esocidae and Percidae, used at water temperatures not exceeding 10 deg C (50 deg F), the required withdrawal period is 21 days. Legal status, approved species and withdrawal rules vary by country and apply to food fish; consult a fish-health veterinarian and the current label before use.