The permeability to water of the eggs of certain marine teleosts

Summary Measurements have been made of the rate of turnover of tritiated water in the eggs of the plaice,Pleuronectes platessa and of the permeability of the vitelline membrane. The rate constant of water exchange in body cavity eggs is 1.0 h^–1, corresponding to a permeability of 0.086 ³/²/sec. When shed into sea water the rate constant of exchange declines to 0.2 h^–1 after 1 hour and to 0.02 h^–1 after one day corresponding to a permeability of 0.0017 [³/²/sec. As the embryo develops the rate of turnover increases again. The buoyancy of the egg is dependent on its low salt content which counteracts the weight of the protein. During development the water loss by osmosis reduces the egg almost to neutral buoyancy.