✔ 最佳答案
http://en.wikipedia.org/wiki/Beluga_sturgeon
Unconfirmed reports suggest that belugas may reach a length of up to 8.6 m (28 ft) and weigh as much as 2,700 kilograms (5,940 lbs), making them the largest freshwater fish in the world, larger even than the Mekong giant catfish or the pirarucu. At this mass, the beluga would be even heavier than the ocean sunfish, generally recognized as the largest of bony fishes. But the largest generally accepted record is of the female taken in 1827 in the Volga estuary at 1,476 kg (3,249 lbs) and 7.2 m (24 ft).[2] Nevertheless, some scientists still consider the Mekong giant catfish to be the largest freshwater fish, owing to sturgeons' ability to survive in seawater.
圖片參考：
http://upload.wikimedia.org/wikipedia/commons/e/e7/Beluga_sturgeon.png
Mekong giant catfish 只有2.7m, 小巫見大巫.
2009-06-07 13:56:34 補充：
Mekong giant catfish ... is widely recognized as the largest freshwater fish ever caught (although sturgeon can far exceed this size, they can be anadromous). Mekong giant catfish have been confirmed as anadromous also.
2009-06-07 14:01:11 補充：
http://en.wikipedia.org/wiki/Mekong_giant_catfish
即係, 其實 catfish都係 spend part of its life in saltwater. 如果beluga sturgeon 不算, mekong giant catfish 都不能算.
