Hello Peter
thank you for such a detailed reply, although I still cannot find Lake Rasau on any map, there are a number of unmarked blackwater lakes in the area you mentioned on Google Earth, so I am guessing probably one of those.
I think I may have bought one of these other “Jambi” species as have great problems identifying them. If you have time, maybe you could have a look at the images posted by Borneo Pisciculture listed and sold as P. gunawani. If you look at August 12th post here and tell me what you think.
Many thanks
Rod