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Gills are needed for ionoregulation before they are needed for O₂ uptake in developing zebrafish, Danio rerio

Peter Rombough^*

Department of Zoology, Brandon University, Brandon, Manitoba, Canada R7A 6A9

View larger version (13K): [in a new window]   Fig. 1. Median survival times (±95 % CI) for 7 days postfertilization zebrafish exposed to various concentrations of MS222 in normoxic fresh water. The dashed line indicates the regression equation based on median survival times (ET50) between 50 and 200 mgl-1. The slope of this line was not significantly different from zero (P>0.05). Values in parentheses indicate the percentage of larvae ventilating their gills at the various MS222 concentrations. 0 % gill ventilation continues as indicated by the horizontal arrow. The vertical arrow indicates <50 % mortality.

View larger version (15K): [in a new window]   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.

View larger version (15K): [in a new window]   Fig. 3. Median survival times (+95 % CI) for 14 days postfertilization zebrafish prevented from ventilating their gills because of exposure to 130 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.

View larger version (14K): [in a new window]   Fig. 4. Median survival times (+95 % CI) for 21 days postfertilization zebrafish prevented from ventilating their gills because of exposure to 150 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.

View larger version (46K): [in a new window]   Fig. 5. 24h median lethal concentrations (LC50) (+95% CI) for 3 and 7 days postfertilization zebrafish larvae exposed to MS222 in normoxic fresh water, normoxic 50% physiological saline and hyperoxic fresh water. Dashed lines indicate approximate median survival times (ET50) for suppression of ventilatory movements. The asterisk indicates a significant difference in median survival time compared with normoxic fresh water within an age class. Numbers in parentheses indicate the number of trials.

View larger version (40K): [in a new window]   Fig. 6. 24h median lethal concentrations (LC50) (+95% CI, N=4) for 3 and 7 days postfertilization zebrafish larvae exposed to phenoxyethanol in normoxic fresh water, normoxic 50% physiological saline and hyperoxic fresh water. Dashed lines indicate approximate median survival times (ET50) for suppression of ventilatory movements. The asterisk indicates a significant difference in median survival time compared with normoxic fresh water within an age class.

View larger version (40K): [in a new window]   Fig. 7. Median survival times (±95% CI, N=4) for 7 days postfertilization agar-embedded zebrafish 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. Sham indicates the median survival time for sham-operated larvae in normoxic fresh water. The vertical arrow indicates <50% mortality.