Sargassum is a free-floating seaweed found offshore in mats throughout the Gulf of Mexico. These mats of vegetation provide crucial habitat for a wide variety of marine animals in the open Gulf.
Sargassumfish as the name implies live amongst the Sargassum plants that can be found on offshore rips. Sargassumfish are members of the frogfish family.
Thanks to Dennis Sweetman for the fish ID.