The swelling egg of the long rough dab, Hippoglossoides platessoides limandoides (Bloch)

The egg of Hippoglossoides platessoides limandoides swells when released into sea water. The swelling takes place entirely outside the ovoplasm and creates a large perivitelline space which can make up 85% of the total egg volume. Swelling occurs in both unfertilized and fertilized eggs although a small proportion of unfertilized eggs, believed not to have been activated, do not swell. Swelling is dependent upon the breakdown of cortical alveoli, together with an unusually soft and elastic chorion. The cortical alveoli, present in greater numbers than is usual in teleost eggs, release colloidal material when they break down on egg activation; adsorption of water by this material is responsible for the egg volume increase.