Species composition and abundance of fishes that escaped from aquaculture facilities during catastrophic flooding in the Paranapanema and Tibagi rivers, in January, 1997 was estimated. In all , 1,292,000 adult individuais belonging to 11 species and 1 hybrid, were introduced into these rivers; only one species was native. The disaster is attributed to the illegal occupation of the river banks, and the non observance of standard measures designed to avoid escapement.