Abstract: Accurate abundance estimate of Baltic clupeids, herring and sprat, is required for their sustainable exploitation. The understanding the sound backscattering of individual fish is important for employing the acoustical techniques, which are widely used in the estimation. The previous studies demonstrated that the improvement of the understanding is critical for the Baltic herring and sprat. It was the main motivation of the paper. The main objective was understanding the difference in acoustic backscattering by herring and sprat in the Baltic Sea. The study was based on a numerical modeling of backscattering by the individual fish. The model input data (morphometric parameters of fish) are obtained using available X-ray images of Baltic sprat and herring. The difference in the backscattered energy, backscattering directivity pattern, and the body contribution into the backscattering of the total fish was demonstrated for the considered species.