From the back cover:
"Evil Denizens of the Depths: The Sahuagin.
This book is the second in a series of accessories that focuses on some of the most popular monsters in the AD&D game. DMs and players alike should also look for Evil Tide, Night of the Shark, and Sea of Blood, a trilogy of Monstrous Arcana adventures centered around the Sahuagin."
Also contains Rules for Underwater Adventures and a poster sized chart of the comparative sizes of Sahuagin and many other sea creatures.