Method and apparatus for producing an oxygenated fluid. In accordance with various embodiments, a vessel of water is provided for housing a population of fish. A stream of oxygenated water is generated to have a dissolved oxygen content of at least about 70 milligrams/liter (mg/l). The stream of oxygenated water is diluted with a second stream of water to provide an output stream with a dissolved oxygen content of from about 5 mg/l to about 14 mg/l. The output stream is injected into the vessel to maintain the population of fish.