Influence of sea water on the osmoregulatory mechanisms of the rainbow trout (Salmo Gairdneri)

• Main Author: Milne, Robert Stephen
• Language: English
• Published: 2010
• Subjects: Seawater; Rainbow trout
• Online Access: http://hdl.handle.net/2429/18865

The effect of S.W. on the osmoregulatory processes of Rainbow trout was studied. Rainbow trout were monitered for various acid--ba.se and respiratory parameters during F.W. - S.W. transfer. Plasma Cl⁻, total CO₂ and HCO₃⁻ concentrations were measured, as well as blood pH, Pa0₂ and PC0₂- V02₂, VG, VCO₂, and VH⁺ were calculated from the measured parameters. During the exposure to S.W. for 3 hours none of the measured variables changed significently, indicating that the Rainbow trout is indeed euryhaline. It appears that unlike the goldfish the trout has a branchial Cl⁻/HCO₃⁻ exchange diffusion pump that is of small capacity, because changes in the external concentrations of CI⁻ and HCO₃⁻ did not affect internal levels of these ions. Raising external Cl⁻ levels would cause a lowering in plasma HCO₃⁻ if there was a Cl⁻/HCO₃⁻ exchange diffusion pump in the gills. A second group of experiments involved the use of Cl⁻ to measure Cl⁻ fluxes in the gills of intact trout. Injections of HCO₃⁻ into the fish did not stimulate Cl⁻ efflux, indicating that if there is a Cl⁻/HCO₃⁻ exchange diffusion pump, it is of small capacity. Gill carbonic anhydrase levels were measured in the gills of F.W. and S.W. trout, S.W. and F.W. coho, and goldfish. Goldfish have a high level as does the S.W. coho. Carbonic anhydrase catalyses the formation of HCO₃ from C02 for the Cl⁻/HCO₃⁻ pump, and is thus indicative of the importance of the pump in Cl⁻ and HCO₃⁻ fluxes.. The significance of the differences in the ionic pumps of trout, coho, and goldfish are discussed in relation to their life histories. Trout having a flexible osmoregulatory system (being euryhaline) while the coho and goldfish are more specialised being essentially stenohaline. === Science, Faculty of === Zoology, Department of === Graduate