It is really not that easy to say which catfish species is the largest one. The two giant asian Pangasianodon are surely the heaviest, reaching weights of around 300 kg in exceptional cases. The confirmed record length for the wels is with 2,78m similar to the longest confirmed length of the Pangasianodons. Brachyplatystoma don´t grow as long as the wels, but it is nearly equal if it comes to weight, because it is stockier and bulkier than the wels, which has a maximum confirmed weight of 144 kg and B. filamentosum of 142kg. Such small differences in weight don´t really count if you keep in mind how this dates can change from eating alone.