An enclosed sea, a distinctive body of water
The surface water of the Black Sea is about half as salty as the oceans. Great rivers such as the Danube, Dnieper and Dniester continually bring it fresh water and nutrients; the dense Mediterranean water entering through the Bosphorus sinks to the bottom and stays there. This creates a thin upper layer of cold, low-salinity, nutrient-rich water, above a silent, oxygen-free depth. All the fish live in the upper hundred to hundred and fifty metres.
Within this narrow layer, the seasons are harsh. In winter, the water falls to eight degrees Celsius, and two plankton blooms occur in spring and autumn. The sea imposes two demands on fish: feed heavily in a short time, and build up fat reserves for winter or migration. The character of Black Sea fish — their fat, texture and aroma — grows out of this necessity.