Mullet are active shoaling fish, found mostly in shallow coastal water, especially over organically-rich and seaweed covered sediments. They are typically found in harbours, bays, lagoons and estuaries, where they may even enter fresh water. Shoals are often seen swimming right at the surface of the water. Mullet feed along the sea-bed by taking in mouthfuls of mud and algae. This is sifted through the large gills so that mostly only bits of seaweed, worms and other edible material are swallowed. They are a hardy fish and it is no coincidence that they are often found in huge numbers around sewage outflows where they feed greedily on any organic matter that they come across.
Its length is typically 30 to 75 centimetres (12 to 30 in).
Mullet have no real teeth and instead rasp away with their thick lips at rocks and pier pillings containing algae and small invertebrates. The stomach acts like a muscular gizzard, and the intestine is very long to cope with the rather poor diet. The most common of the grey mullet is the thick-lipped grey mullet but there are also thin-lipped and golden varities that can be found in Irish waters.