Welcome to the forum, mate!
Beautiful fish. Mine 3-4-year old is stuck at ~30 cm too. Refuses to grow farther. Can see him here:
http://www.planetcatfish.com/forum/viewtopic.php?f=4&t=36786&hilit=+opportunity
1. It may or may not matter to you but thanks to the work of Dr. Heok Hee Ng (aka Silurus on Planet Catfish), the genus of Hemibagrus has been most heavily re-worked.
From 3 species it went to 32 species! If you care to read the original revision, there appears to be a group of nemurus-like hemibagrus, all very similar but at the same time distinctive species.
http://www.planetcatfish.com/common/genus.php?genus_id=13
2. Reproduction.
PCF:
http://www.planetcatfish.com/common/species.php?species_id=801 "The fish spawn in pools within rivers or within the flooded forest, usually depositing the eggs in a substrate of leaves and twigs. The parents apparently exhibit brood care."
FishBase (note that Dr. Ng's revision is very recent and is not even reflected on FishBase yet):
http://www.fishbase.us/summary/Hemibagrus-nemurus.html "Moves into flooded forests to spawn and the young are usually first seen in August."
AFAIK (which is not far) and can deduce, I think that they will not reproduce naturally in any small body of water because they undertake a significant migration to the spawning sites, not to mention that one will have to mimic the seasonal weather fluctuation (water level, temperature, chemistry, which is changed by lots of rain, turbidity, current, etc.) to trigger them. They may also spawn then and there because of the great lots of other fish spawning and flooding the water with hormones.
On farms in SE Asia, they are artificially reproduced for food being a praised food fish.
