The recovery and hematological rehabilitation of chlorine stressed adult rainbow trout (Salmo gairdneri)

Synopsis The ability of adult rainbow trout (Salmo gairdneri) to recover from acute chlorine exposure was tested. Six separate tests were carried out in duplicate. Blood was collected from each duplicate group of fish at the beginning of the test, at the appearance of the chlorine-distress symptoms, and at 24 and 48 h after exposures. The total residual chlorine (TRC) concentrations used in these six tests were 1.67, 3.50, 1.10, 1.25, 1.02 and 0.0 mg 1^–1, at water temperatures of 13.5, 14.6, 17.2, 22.6, 23.0 and 26.0° C, respectively. The cumulative fish mortality for these six tests at 48 h after exposure were 11.5, 100, 0.0, 67.1, 36.1 and 100 percent. Blood of chlorine stressed fish exhibited signs of hemoconcentration and hemolysis. All blood parameters with the exception of hemolysis returned to control levels within 24 hours after exporsure. High TRC concentrations in the range of 3.5 mg 1^–1 at 14.0° C, and TRC of 1.25 and 1.02 mg 1^–1 TRC at 23° C, significantly diminished the rainbow trout recovery.