A brief description is given of both a wideband echo-sounder and data acquisition at sea, Experiments were conducted in the Bay of Biscay al various seasons for four years. Fish species were identified by trawling. Only echoes associated with trawl catches that were monospecific were used in the classification analyses. Species discrimination was based only on the spectral signature of the echoes and did not take into account the characteristics of the school shape. A modelling of the power spectrum of the echo was used to limit the spectral signature to a reduced set of parameters that could be used for classification using a neural network. Thirty-six different monospecific schools, including about 900 echoes, were processed. Three species were considered: sardine (Sardina pilchardus), anchovy (Engraulis encrasicolus), and horse mackerel (Trachurus trachurus). Classification performance had a success rate as high as 75%.