Sardinella tawilis (sometimes obscurely referred to as the freshwater sardinella) is a freshwater sardine found exclusively in the Philippines. It is unique in that it is the only member of the family Clupeidae that is known to exist entirely in freshwater. Locally, they are known in Filipino as tawilis.
S. tawilis are small fish reaching up to 15 cm and weighing less than 30 g. Like other members of their family, they have laterally compressed bodies with bellies covered in tough scale-like scutes. They have a single, triangular dorsal fin and a forked caudal fin. They possess long, slender gill rakers in their mouths.
Tawilis populations are found only in a single lake on the island of Luzon in the Philippines. Taal Lake, a large body of water in the province of Batangas that used to be the caldera of an ancient volcano. Before recent history, the lake was but an extension of the entirely-marine Balayan Bay. A major eruption in the 16th century essentially sealed the lake from the sea, eventually leading to its waters becoming non-saline. Sardinella tawilis is believed to be one of a few formerly-marine species trapped within the lake that have evolved into purely freshwater species.