Amblygaster leiogaster, the smoothbelly sardinella, also known as blue sardine, blue sprat, bluebait, is a reef-associated marine species of sardinella in the herring family Clupeidae.

It is found in the marine waters along Indo-West Pacific regions south towards western Australia.

The flank is gold in fresh fish but becomes black while preservation.

It is rather closely resemble Amblygaster clupeoides, but the latter has very few lower gill rakers than smoothbelly sardinella.

The fish feeds on minute organisms like zooplankton.