The arapaima is by far as big as many people think. They reach sometimes exceptional lengths of more than 2,5m, sometimes around 2,7m in very very rare cases, but are not as heavy as the giant Pangasianodon gigas and Pangasianodon santiwongsei. The giant piraiba is recorded at more than 140kg and about 2,3m or so. The largest wels on record was 2,78m and weighed 144kg. The chinese paddlefish´s size is most probably also highly exagerated, but it is very probable that this species reaches a length of more than 4m. I think this species rivals together with the giant freshwater stingray for the longest freshwater fish, but both species have either a long snout or a long tail, and are not really best examples for pure length. In matters of length the wels is recorded with a bigger length then the giant Pangasianodons, piraibas and arapaimas, but is not the heaviest. The giant allogator gar can also reach similar lengths in exceptional cases. All the giant freshwater stingrays from which I read had only estimated weights, it seems that none of them was actually weighed, so I would be very critical about their actual weight. Untill now, the giant Pangasianodon gigas seems to be the heaviest pure freshwater fish with an authenticated weight.