Attenuation of sound by schooling fish was measured or estimated for yellowtail (Seriola quinqueradiata), sea bream (Pagrus major), and spotted mackerel (Scomber australasicus) in culture nets and a net cage. The results, along with those of other researchers, are normalized to obtain extinction cross sections per 2/3 power of the body weight. In the normalized cross sections there are no large differences among fish species, sizes, and measuring methods. The attenuation increases slightly with the frequency. Attenuations to be encountered in field observations by echo sounders are estimated and the results reveal that ordinary fish schools do not attenuate sound significantly.