海産魚の体液ならびに環境水の浸透圧に関する研究-II

Abstract

Observations were made on the temperature and chlorinity of the sea water, in which shoals of mackerel Scomber japonicus and Jack mackerel Trachurus japonicus were found. The freezing-point depression of the sera and the state of maturity in these species were also examined monthly for two years in the fishing grounds of the East China Sea. In the course of migration, the osmotic pressure of body fluids rose significantly as the maturity of the fish progressed, showing a maximal value averaging 12 Atms. at the time of spawning. This value remained unchanged until the ripe eggs had been completely dis-appeared from the ovaries, but then dropped gradually to 6 Atms. The osmotic pressure of the environmental sea water also varied to a certain extent (no more than 5%) corresponding to the change of that of body fluids. The difference between both osmotic pressures was reduced owing to a great increase in serum osmolality. The least difference occurred at spawning times. After spawning, however, the fish moved into waters of a constant osmotic pressure. They therefore migrated towards waters of higher chlorinity when the water temperature grew colder in the winter time. Hence, the difference between the osmotic pressures of the body fluid and the sea water returned to the original state.