all the outside tanks looked like this, although of course they differed in length. They were all incredibly difficult to see inside due to the dark water and reflections off the glass.
I think these fish are [i]Wallago attu[/i].
See my review here for more details:
http://www.zoochat.com/2182/zoos-burma-6-kandawgyi-fresh-water-362192/
