Fig. 2. Median survival times (+95 % CI) for 7 days postfertilization zebrafish prevented from ventilating their gills because of exposure to 100 mgl^-1 MS222 in normoxic fresh water, normoxic 50 % physiological saline, hyperoxic fresh water and hyperoxic 50 % physiological saline. Asterisks indicate significant differences in median survival times compared with normoxic fresh water. Numbers in parentheses indicate the number of trials.