Pigfish

Found in schools, close to shelter during the day, dispersing at night, foraging for food, over mud, and sandy bottoms, of coastal waters
They feed nocturnally on benthic crustaceans and small fish.

In some areas of the world 'Grunts' are better known as 'Sweetlips' distinguished from other species by their very large rubbery lips.
'Grunts'because they "grunt," the grunting sound is produced by their flat teeth plates rubbing together and this is amplified by their air bladders.
Found either singly or in schools hovering or motionless over the reef during the day, becoming nocturnal predators.