Osmoregulation in Juvenile and Adult Lampreys

Abstract

Nonparasitic lampreys are well adapted for a freshwater existence but are less tolerant of salt water than representatives of the parasitic species. Anadromous feeding juvenile sea lampreys, Petromyzon marinus, are able to control serum osmotic and ionic concentrations in all salinities between 0 and 34‰. Juveniles of the anadromous European river lamprey, Lampetra fluviatilis, are slightly less tolerant of salinity change. The transition of P. marinus to a landlocked existence has resulted in a reduction in the capacity for marine osmoregulation. Tolerance to salt water among landlocked P. marinus is related directly to size emphasizing the advantage afforded through a reduction of surface area relative to body volume. Changes in serum osmolality are primarily the result of corresponding shifts in sodium and chloride ions. Changes in chloride are not accompanied by an equivalent shift in sodium suggesting that the relationship between the two ions is not passive. Regulation of sodium by landlocked P. marinus is not precise as that exhibited by the anadromous form particularly in the higher salinities. Nontrophic upstream migrant lampreys display a reduction in their marine osmoregulatory mechanisms and a restoration of the freshwater osmoregulatory apparatus. Freshwater osmotic and ionic regulation deteriorates in spent adult lampreys.Key words: blood, ionic regulation, osmotic regulation, parasitic and nonparasitic lampreys, salinity, life cycle