On the Respiration of the Killifish Oryzias Latipes

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Abstract
1. Factors influencing respiration in this small surface-living freshwater fish (100-290 mg body weight) have been investigated using through-flow respirometers. 2. When the rate of flow over the resting fish is increased, there is an increase in oxygen consumption, but no marked change in ventilatory frequency. Percentage of oxygen removed from the water during its passage over the fish decreases with increase in flow rate in some ranges, and seems to increase again with even greater flow rates notwithstanding a rise in oxygen consumption. 3. The standard oxygen consumption is in the range 250-400 c.c./kg/h at 20°C, and 300-500 c.c./kg/h at 25°C with average flow rates (50-150 c.c./h). 4. Oxygen consumption of the fish is directly related to ambient POO2 over the range 40-500 mmHg. Increases both in ventilatory frequency and in percentage of oxygen removed from the water during its passage over the fish occur during hypoxia, but decrease with increases in ambient POO2 although O2 uptake increases. 5. Ventilatory frequency decreases during darkness and increases in light. After stimulation with light both oxygen consumption and percentage of oxygen removed showed temporary high rates which only gradually subsided. 6. Ventilation volume, measured directly by collecting the water which had passed over the gills, is about 800 c.c./min/kg at 25°C, when the positive hydrostatic pressure is about 5 mm of water. 7. Determinations of gill areas of the fish gave values in the range of 1211-1700 mm2/g weight. The larger values in the fish are probably related to its greater oxygen consumption. 8. Slow potentials associated with respiratory movements were recorded around the head region of the fish by means of external platinum electrodes. When the active electrode was shifted tailwards along the body, the size of the potentials changed, being maximal just posterior to the opercular opening and rather large beside the mouth. The higher values obtained in the potential were 900-1100 µV. The polarity of the potential was reversed at a position anterior to the gill opening.

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