Thanks there for all the comments. They are all around 11~12" and the length of the reedfish make it safer from been the food of channa. On the other hand, I feed them pretty well, that helps to minimize the aggressiveness of channa. Infact, I would not suggest anyone to do such combination. Don't try this at your place.
As for the photography (jelly), the way of lighting is very important of all. I bet you use internal flash to take shot. 1st of all, strong enough lighting makes you good photography conditions such as faster shutter speed to freeze action, wider DOF to get full clear perspective fish photo, and good auto focus ability. Roughly estimated, I use 300~400W lights when doing photography. Top down lighting is always the best for presenting the fish is a natural way (most light source are top down including sun light). You can either use stronger tank light or use external flash (wired or wireless whatever, if your camera has this ability).
Well, I have to say beside the photography gears, take more shots is a good way to improve the skill. I shoot out the 1GB CF card in each photo session, there certainly are some OK shots.