Meeting Abstract
In many experiments, euthanasia, or humane killing, of animals is necessary. Some methods of euthanasia cause death through cessation of respiratory or cardiovascular systems, causing oxygen levels of blood and tissues to drop. For experiments where the goal is to measure the effects of environmental low oxygen (hypoxia), the choice of euthanasia technique, therefore, may confound the results. This study examined the effects of four euthanasia methods commonly used in fish biology (overdose of MS-222, overdose of clove oil, rapid cooling, and blunt trauma to the head) on variables known to be altered during low oxygen exposure (hematocrit, plasma cortisol, blood lactate, and blood glucose) and on variables reflecting gill damage (trypan blue exclusion) and energetic status (ATP, ADP, and ATP:ADP ratio). These variables were measured in Gulf killifish, Fundulus grandis, after exposure to normal or reduced oxygen levels (24 h at 0.86 mg O2 l-1; = 17 mm Hg = 2.2 kPa). During these analyses, it was necessary to modify the technique for ATP and ADP measurement due to high calcium content of the biological samples (intact gill arches). Regardless of method of euthanasia, hypoxia led to higher hematocrit, blood lactate, and plasma cortisol. Independent of oxygen level, MS-222 led to higher hematocrit and lower gill ATP:ADP ratios compared to other methods of euthanasia. Thus, the choice of euthanasia method should be appropriate for the experimental design, species studied, and variables measured. For hypoxia research, in particular, caution should be exercised when using methods that act through respiratory or cardiovascular arrest.
