Complex sentence: The country's fresh water basins and the Caspian Sea account for 97 species of fish of which eight introduced and seven of these have become widespread and over 15 thousand species of invertebrates in Azerbaijan.
Split into simpler sentences: The country's fresh water basins and the Caspian Sea account for 97 species of fish of which eight are introduced and seven of these have become widespread. There are also over 15 thousand species of invertebrates in Azerbaijan.