Well, don't forget that there are quite a few different fish imported under the generic 'Wallago' label that are commonly imported. Ompok spp. cats are frequently confused for Wallagos, and they stay considerably smaller. Plus, there's more than one specie of Wallago, and not all are giants like the attu. Trying to get a good ID on those cats is very difficult, too, because so little research has been done on that complex.