PURPOSE:  The purpose of this policy is to standardize the practices of using buffered MS-222 (tricaine methane sulfonate) for euthanasia and anesthesia of fish and other cold blooded aquatic animals, and to provide recommendations to investigators and personnel for its safe and appropriate use.


Preparation:  MS-222 is not regarded as a toxic chemical by OSHA classification but according to the MSDS, MS-222 “may be irritating by inhalation, ingestion or absorption through the skin.”  Also, some literature suggests that MS-222 is a potential mutagen/carcinogen. Therefore, whenever preparing a stock solution with the powdered form of MS-222 all work should be done in a well ventilated area (outside in the field or under a fume hood in the laboratory) and protective clothing is required.  This includes a lab coat, chemical resistant gloves (e.g. nitrile), dust mask and goggles. If work is done in a fume hood the dust mask is not necessary.  When handling the prepared solution, a lab coat, gloves and eye protection are required.

Pharmaceutical grade MS-222 must be buffered with sodium bicarbonate resulting in a pH between 7.0 and 7.5.  Two examples of pharmaceutical grade MS-222 are Finquel and Western Chemical’s Tricaine-S.

Storage:  Powdered and prepared solutions should be stored in a dark brown bottle and kept refrigerated or frozen if possible. Prepared solutions should be clearly labeled with the name of the drug, concentration, and the date that the solution was prepared. Replace solution monthly or any time the solution begins to exhibit a brown coloration.


Liquid (up to 300 mg/L)

Anesthetizing (0.1 mg/ml) and euthanizing (200-300 mg/L) dilutions can both be disposed of in a sanitary sink drain following the guidelines outlined below: 

  • Anesthetizing dilutions (0.1 mg/ml) require flushing using at least one liter of water. 
  • Euthanizing dilutions require flushing with 15-20 times the volume of water used for euthanizing fish. 
  • If MS-222 anesthetizing and euthanizing solution volumes are under one-liter, the volumes can be disposed of at one time. 
  • If the MS-222 dilutions exceed one-liter, sink disposal should be limited to one-liter per day. 
  • If in a remote location where a sewer may not be readily available, further dilute the solution with water and dump wastes on land, in a location away from water. 

MS-222 crystal form and solutions exceeding 300 mg/L

Material supplied by the manufacturer (crystal) or a higher concentration stock material (exceeding 300 mg/L), should be labelled as a non-hazardous waste for pick-up and disposal through UW-La Crosse’s hazardous waste vendor.  Disposal and waste pickup should be arranged through Environmental Health and Safety.

Non-hazardous Fish carcasses after euthanization with MS-222

Fish carcasses <7dpf can be flushed down a sanitary sink drain.

Fish carcasses >7dpf resulting in volumes < 8L should be double bagged and frozen.  Bags can then be disposed of as non-hazardous waste.

Fish carcasses exceeding 8L should be double bagged and frozen.  Disposal and waste pickup should be arranged through Environmental Health and Safety.

Prepared by:  Amy Cooper

Adoption Date: 9/13/16
Amended: 7/12/17
Reference minutes: 9/13/16, 7/12/17, 2/7/18