Branchial Ionic Flux Responses in Rainbow Trout to Chloramine-T after Acclimation to Different Levels of Water Hardness

Abstract

Whole-body unidirectional and net Na⁺ and Cl^– fluxes were determined in rainbow trout Oncorhynchus mykiss exposed to chloramine-T (9 mg/L) alone or in combination with 17 mmol NaCl/L (0.1 % weight per volume, w/v) after acclimation to either city of Ottawa tap water (TW: Na⁺ 0.121 ± 0.004 mmol/L; K⁺ 0.015 ± <0.001 mmol/L; Ca²⁺ 0.351 ± 0.004 mmol/L; Cl^– 0.141 ± 0.002 mmol/L) or artificial soft water (ASW: Na⁺ 0.043 ± 0.003 mmol/L; K⁺ 0.005 ± <0.001 mmol/L; Ca²⁺ 0.063 ± 0.002 mmol/L; Cl^– 0.026 ± 0.002 mmol/L). Preexposure fluxes revealed that ASW-acclimated fish had reduced rates of Na⁺ uptake and efflux compared with TW-acclimated fish. However, rates of Cl^– uptake among ASW-acclimated fish were comparable with those of TW-acclimated fish. Exposure to chloramine-T in TW resulted in significant increases in the Cl^– efflux, giving rise to a significant and negative net flux. Exposure of ASW-acclimated fish to chloramine-T caused a significant negative increase in the Na⁺ efflux and net flux but only a negative increase in the Cl^– net flux. The addition of 17 mmol NaCl/L (0.1% w/v) eliminated the negative net ionic fluxes, resulting in significant increases in influx. The combined use of chloramine-T with NaCl is a potential method of remediating ionic disturbances that may be caused by treating trout with chloramine-T.