Some studies were made so as to understand the fate of some marine organisms that inhabit bodies of water, both very isaline and brackish as it is between the North sea and the Baltic sea which have given rise to several physiological problems.
The physical properties studied were the specific gravity and diameter changes taking place on some fish egg species most common in the Baltic sea and the North sea. The spawning season of the species studied takes place from December (November) to July (August) of each year. The spawning period for each species lasts from 2 to 4 months, some of them overlapping each other.