The Mechanism of Marine Osmoregulation in the Lampern (Lampetra Fluviatilis L.) and the Causes of Its Breakdown During the Spawning Migration

ABSTRACT Some fresh-run lamperns can osmoregulate in 50 % sea water (Δ = 0·970° C.), where they can maintain plasma freezing-point depressions of about 0·57° C. An analysis of the mechanism of osmoregulation in these animals shows that it is similar in many respects to that employed by marine teleosts. The lampern swallows sea water and absorbs a solution containing a high proportion of monovalent ions into its blood. It has been calculated that chloride is excreted by an extra-renal route, presumably by means of chloride excretory cells which have been discovered in the gills. The rate of extra-renal loss of water is high and the urine output is negligible. Many fresh-run animals are unable to osmoregulate. In some cases the capacity to swallow sea water becomes reduced, whilst in others the number of chloride excretory cells is diminished—an indication that the extra-renal excretory mechanism is failing. Both of these mechanisms regress simultaneously in some animals.