Monitoring the depth of anesthesia becomes increasingly difficult as the fish loses its equilibrium, stops swimming,
fails to respond to deep pressure, and subsequently ceases any oper cular activity. Slow and steady opercular movements
without response to physical stimuli are desirable. On larger animals, an electrocardiogram (ECG) may provide valuable
information about heart rate as well as atrial and ventricular activity. With hypoxia for instance, the T-wave amplitude
will increase as an irregular rhythm is observed (Harms and Bakal 1994).