Effects of freshwater to seawater transfer on osmoregulation, acid-base balance and respiration in river migrating whitefish (Coregonus lavaretus)

Osmoregulation, acid-base balance and respiratory parameters were investigated in whitefish following transfer from freshwater to salt water. Whitefish acclimated successfully to 25 ppt brackish water but died after direct transfer to 32 ppt sea water. Transfer to brackish water induced rapid (<6 h) and permanent increases in plasma [Na+], [Cl−], total [Ca] and [Mg].

The extracellular hyperosmolality effected a transient (<3 days) muscle tissue dehydration and red blood cell shrinkage. Exposure to brackish water decreased both the arterial O2 tension and whole body O2 uptake. The extracellular acid-base status changed from an initial respiratory acidosis at 1 h towards a pronounced metabolic acidosis at 48 h of brackish water exposure.

Red cell pHi decreased in parallel with extracellular pHe, but the in vivo ΔpHi/ΔpHe was only 0.26, suggesting some selective protection of red cell pHi. Plasma cortisol concentration and gill Na+, K+-ATPase activity increased after exposure to high ambient salinity, reflecting the induction of hypo-osmoregulatory mechanisms.

The physiological changes in whitefish are discussed in relation to salinity-induced effects in other salmonid fishes.