The stomach content of 542 specimens of youngs of Sardinella aurita was investigated for ecological purposes. The fishes were divided into four lots according to the region where they were fished. Lot I was collected at the "Ponta de Feiticeira", in the Island of S. Sebastião where the main food was found to be copepods. Lot II comes from the beach of "Rabo Azêdo", also in the Island of S. Sebastião, the more abundant food here consisted of ostracods. Lot III, captured at Cananéia, had been feeding mainly on diatoms. A large percentage of the fishes of Lot IV which were gathered at Santos, had empty stomachs and the major part of the remainder had ingested sand. It may be concluded that Sardinella aurita feeds on plancton in a general way similarly to Clupea pilchardus and therefore is euryphagous. It is interesting to note that the fishes from Santos had probably found themselves in a food-deficient environment as regards plancton, this being apparently the reason of having ingested sand. According to local information, the first occurrence of schools of Sardinella aurita in the lagoonal region of Cananéia was only noted about 12 years ago. Previously the species was found only outside in the open sea. A supposition is presented that biological changes are in process.