It's most likely stressed from being in too small of a tank and with too much lighting. You can try adding floating plants (plastic or real) to diffuse the lighting. This fish needs a larger tank sooner than later.
I would expect it to grow at least another foot.
Read post #5 for more info.
http://www.monsterfishkeepers.com/f...90-CHANNA-SPECIES-GUIDE-UPDATE-IN-PROGRESSION
Here's a good example of what a C. Marulius look like when they are not stressed. (Not my video)
[video=youtube;nb1lHHYYeuE]http://www.youtube.com/watch?v=nb1lHHYYeuE[/video]
Just google Channa Marulius and you will find some good photos and care sheets.
Good luck.