How long have you had him? and how long was he in the mail?
As for right now, I am thinking two things.
1) He is still stressed from shipping and his ammonia level might of been a bit high
2) Different water chemistry from where he came from and where you are - I don't mean ammonia, nirates but like water hardness and PH. I know if the levels are vastly different and if they arenot acclimated very slowly, it can cause problems.
The only fish I have gotten in the mail were plecos. Had to go through 3 different sellers before I got 2 that were healthy and well packaged.
I would think the best thing for him right now is clean, warm water and maybe some darkness to allow him to destress a bit. Stress coat will help with fin regrowth if you have it.
Indiam Almond Leaf is usually only avalible via sellers in Asia. It's good to have on hand and releases tannins into the water. Normally the leaf will turn the water amber colored, which mimics the water in their natural enviroment. Supposedly it also helps them spawn, lowers PH too. If you decide to get some, I recommend AMY on ebay. I have gotten the cheaper leaves she sells and they are still in good shape - even if she gives them a C rating. Since you just drop the leaf in the tank, I really see no reason why the leaves need to be perfect looking.
here is one of her auctions:
Dried Oak leaves supposedly have a similar effect to IAL.