Since the fry of certain species of fish cannot tolerate even slight amounts of supersaturation, their water supplies must be degassed. Gas content can be reduced to subsaturated, sublethal levels by passing it through the vacuum degasser described here. The system includes a low-cost, flow-through unit easily capable of degassing (to less than saturated conditions) water flowing at 190 liters min−1. In tests completed to date, dissolved oxygen content was never reduced below 7 ppm.