PBT has a small hump

[Ace Park]

I leave my nano fish tank alone five days due to a short trip.
After came back home I realized that my PBT has a small hump on his belly as attached. It cannot be taken more clearly but would you share your idea what actually is this?

 

[HumbleFish]

Doesn't look too serious to me (at this point). Could be damage from fighting with another fish, or a cut from a rock or coral sting.

Btw, just how big is your nano fish tank?

 

[Ace Park]

Tank size

Tank size

Doesn't look too serious to me (at this point). Could be damage from fighting with another fish, or a cut from a rock or coral sting.

Btw, just how big is your nano fish tank?

HumbleFish,
Thank you for your comment.
Mine is 18 inch cubic and he is being acclimated in the separate area for a while so there is no possibilities what you expedited.
For your reference, he was adopted 10 days ago, approx 2.5 inch size. He enjoys pellet as well as nori but still a little bit skinny because I can't feed him over four days.

 

[ca1ore]

If the hump is visible on both sides, it may simply be internal stuff showing through because of it being skinny?

 

[Ace Park]

No, it shows on his left side only.

 

[Crimson]

Are you keeping this tang in a 26 gallon tank?

 

[Ace Park]

Crimson,
Thank you for your comment.
I know my tank is small to keep him well but struggle to maintain its best condition.

 

[Ace Park]

Detailed picture of him

Detailed picture of him

http://postfiles4.naver.net/20140207_291/l2cache_1391706585942GJyFY_JPEG/DSCF7242.JPG?type=w2
http://postfiles11.naver.net/20140207_202/l2cache_1391706586345IEWhE_JPEG/DSCF7243.JPG?type=w2
http://postfiles3.naver.net/20140207_194/l2cache_1391706586902JXyKR_JPEG/DSCF7244.JPG?type=w2
http://postfiles8.naver.net/20140207_215/l2cache_1391706588559M4t1z_JPEG/DSCF7247.JPG?type=w2