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Abstract
An apparatus was constructed to determine the ability of fish to swim against currents of known velocity in water of various dissolved oxygen content for periods of one or two days. Fish were tested in currents of 0.8 and 1.2 feet per second at dissolved oxygen concentrations of two milligrams per liter and higher. The ability of juvenile chinook salmon (Oncorhynchus tshawytscha) to resist the above currents is in part dependent on their size. Only chinooks over fifty millimeters in total length were able to swim for a day against a current of 1.2 feet per second in water with dissolved oxygen content near the saturation value. In water with a mean dissolved oxygen concentration of 3.0 miligrams per liter or greater, in all experiments but one, juvenile chinook salmon were able to swim for at least one day against a current of 0.8 foot per second. In all tests at mean oxygen concentrations less than 2.84 milligrams per liter, some fish were unable to swim for the one-day period. In experiments at mean dissolved oxygen concentrations above 2.96 milligrams per liter, all juvenile coho salmon (Oncorhynchus kisutch) were able to swim against a current of 0.8 foot per second for two days. At oxygen levels between 2.0 and 2.7 millgrams per liter, some of the juvenile cohos were able to swim for two days. Largemouth bass (Micropterus salmoides) during September were able to swim against a current of 0.8 foot per second for one day at 25° C. in water having a mean dissolved oxygen content of 2.0 milligrams per liter. In early December, at temperatures of from 15.5 to 17° C., though the bass could swim against the 0.8 foot per second current when the water was nearly saturated with dissolved oxygen, they were unable to do so by the time the oxygen was reduced to 5.0 milligrams per liter.