Methemoglobin Levels in Channel Catfish, Ictalurus punctatus, Exposed to Nitrite and Tricaine Methanesulfonate

Channel catfish (Ictalurus punctatus) were exposed for 24 h to one of the following: 4.0 mg/L nitrite, 4.0 mg/L nitrite + 40 mg/L TMS-222, 40 mg/L TMS-222 and control in which neither chemical was added. Methemoglobin concentrations reported as percentage of total hemoglobin equalled mean ± SD (n) 65.9 ± 10.8 (10), 45.7 ± 9.1 (15), 13.7 ± 5.9 (26), and 2.2 ± 0.4 (10) in the four groups, respectively. Mean methemoglobin in each o f the three treatment groups was significantly greater than controls and significantly different among each other. As expected, nitrite-induced methemoglobinemia was slightly reduced in the presence of TMS-222 for this short-term exposure. The most important finding was that catfish exposed to TMS-222 had methemoglobin levels 6 times greater than those of controls.