Anesthetizing With CO2
Tech Talk 51
High levels of dissolved carbon dioxide (CO2) can be used to anesthetize fish prior to handling for purposes such as weighing, injecting, vaccinating, inspecting and slaughtering. Caution: Carbon dioxide gas can cause drowsiness, blackouts and even death in humans and animals. Use only in well-ventilated spaces or outdoors.
- Buffer the water with sodium bicarbonate (baking soda, NaHCO3) to a pH of 7.5 (or higher if normal for the ASN).
- Using an ultra fine diffuser (or a downflow bubble contactor such as an AES oxygen saturator), bubble carbon dioxide gas into the buffered water (remember, any carbon dioxide bubbles that escape at the surface are wasted gas, so use either an ultra fine pore diffuser or a venturi at the greatest possible depth).
- When anesthetizing for temporary handling, be careful not to supersaturate the water with gases, causing bubble gas disease. When in doubt, check with a saturometer, which measures total gas pressure (TGP, which above 103 percent may cause problems). A vacuum de gassing tower may have to be used prior to carbon dioxide supersaturation.
- When anesthetizing for temporary handling, run the carbon dioxide level up to about 75 ppm. When anesthetizing prior to slaughtering, 250 ppm or more is required.
- Hold the fish in the high carbon dioxide water until the fish slow down or become immobile, as your requirements dictate.
- To revive them, simply put them back into water without carbon dioxide.
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