Sodium balance in the eggs of the Atlantic salmon, Salmo salar.

Although the eggs of salmon and trout have long been of interest to physiologists the extent to which the eggs are permeable to sodium ions is not clear from previous accounts. Freshly stripped salmon eggs contain 2-3 /t-equiv. Na/egg. During embryonic development the quantity of sodium in the egg remains approximately constant (Hayes, 1949), but sodium balance in the freshly stripped egg is complicated. From experiments with freshly stripped eggs in hyperosmotic saline, containing 0*55 MNaCl/1., Kalman (1959) inferred that some sodium penetrated into the yolk, but nevertheless the sodium concentration in the yolk remained much lower than in the medium. Parry Howells (personal communication) has reported that the periviteUine fluid concentrates sodium ions in the water-hardened egg. In order to clarify the situation the exchange of sodium has been examined in freshly stripped, waterhardened eggs, and in eggs in the eyed stage.