Is mullet a freshwater fish or a marine fish?

Sea fish.

According to the World Fish Database, mullet is an offshore pelagic fish. It likes to live in shallow seas or estuaries at the junction of saltwater and freshwater.

Mullet is a fish of the family Mullidae and genus Mullet. The body is long and stout, the front part is nearly cylindrical, and the back part is flat laterally. The head is short, flat, slightly raised on both sides, the muzzle is wide and short, and the eyes are medium-sized, mostly covered by a thick lipid film, commonly known as white eyes. The distance between the eyes is wide and flat, there are 2 nostrils on each side, the mouth is located downward, in a figure-eight shape, the teeth are fine and downy, there are teeth on both the upper and lower jaws, the gill openings are large, the operculum membrane is not connected to the isthmus, the operculum strips are 5, and the false gills Well developed, with fine gill rakers.