We can infer from the passage, that grilling ……

A multitude of different fish are caught in the Bosphorus and the Marmara Sea, which is the migration route for millions of fish making their way between the Black Sea and the Aegean every year. So the people of Istanbul are accustomed to eating fresh fish in every season. As well as being abundant and fresh, the fish caught here are full of flavour, since fish from the cold Black Sea areas already have an increased oil content before they begin migrating in autumn, and in the even colder waters of the Bosphorus the oil content rises still further, making these fish perfect for grilling.