What is "sargassum fish"

n. small fantastically formed and colored fishes found among masses of sargassum

The sargassum fish, anglerfish, or frog fish, Histrio histrio, is a frogfish of the family Antennariidae, the only species in its genus. It lives among Sargassum seaweed which floats in subtropical oceans. The scientific name comes from the Latin histrio meaning a stage-player or actor, and refers to the fish's feeding behaviour.