Effect of TRIS and bicarbonate as buffers on anesthetic efficacy of tricaine methane sulfonate in zebrafish (Danio rerio)

Tricaine methane sulfonate (TMS), often called MS-222, is the most common anesthetic used with fishes. Because it is very acidic (pKa about 3) it must be neutralized especially when used in soft fresh water. Much of the literature on fish anesthetics recommends neutralizing with bicarbonate. However, much of the zebrafish literature uses the protocol in "The Zebrafish Book" that recommends neutralizing with TRIS. Three considerations when comparing these buffers are: first, TRIS has the advantage that the pH tends to remain constant, whereas the pH of solutions containing bicarbonate tends to increase as CO2 diffuses from the water to air; second, the CO2 produced by bicarbonate may have some sedative effects in and of itself; and third, there is some evidence that the efficacy of TMS changes with pH. In the present study, we compared the efficacy of TMS using these two buffers and show that there is no substantial difference in anesthetic properties in zebrafish.