EVALUATION OF A LOW HEAD OXYGENATOR AT GIANT SPRINGS STATE FISH HATCHERY, GREAT FALLS, MONTANA

Oxygen content of water is often the primary limiting factor for fish production, as it was at the Giant Springs State Fish Hatchery, Great Falls. Montana. Spring water supplying the 24 outdoor rearing raceways has a dissolved oxygen concentration of only 6.2 ppm and is also supe rsaturated with gas, primarily nitrogen. The low head oxygenator (LHO) manufactured by Zeigler Brothers. Inc., was tested. The units were ev aluated to determine absorption efficiency, degassing ability, and eff ect on fish performance. The LHO units efficiently increased the DO, r educed nitrogen from 120 to 110% saturation, and reduced total gas fro m 112 to 108%. Carrying capacity of raceways with the LHO units was at least 2.2 times greater than that of the controls at the time the tes ts were ended.