In this paper, data collected during 1965--1970 from Bohai Sea, Yellow Sea and East China Sea, on the characteristics of sound of croaker (sciaenoid fishes) with a greater sound-producing mechanism are analyzed and assessed. Spectrum analysis and data-processing were conducted in four different ways for the same sample. The value of basic parameter in sound power spectrum, such as spectral structure,distribution of spectral peak,etc. were obtained accordingly for six different fishes groups. It is indicated that the sound production of each species varied diurnally, and the differences were exhibited in different species and locations. The sounds of the sciaenoid fishes are produced by the vibration of muscles around or attached to the swim bladder. Their acoustic signal is of lower freguency, its frequency bandwidth is narrow, ranging about 400-1000 Hz, and the tones are monotonous about one octave. It was shown by analysis that the sound production of aggregate fishes did not coincide with the common opinion that the greater the velocity of water current, the stronger the intensity of aggregate sound.According to the characteristics and regularities of the sound production, it may be postulated that the sounds are likely to be means of communications of the fishes.