You'll know that its not trout if it was kept with a peacock bass and a rainbow shark. Looks like its one of these cyprinids from Asia. Possibly a zacco species or closely related to.
I'm not seeing tarpon here. The head/upper jaw look wrong, the dorsal is too far back and lacks a streamer, and the eye is too small to be an Indo-Pacific tarpon. It also has markings on the side... I have never seen a patterned tarpon.
I agree with MN_ that it looks like an Asian cyprinid species. Doesnt look like a Zacco species to me though.
I googled "Zacco"just to back check, and it turned up this picture, which doesnt look like any of the other results but bears a striking resemblance to the OP's fish, though this individual looks a bit smaller. http://www.biolib.cz/IMG/GAL/131385.jpg
Also, I believe there are a few species of cyprinid that are given the name "trout" in some Asian countries. This could explain the OP's confusing the fish with a salmonid trout.
Just googled burmese trout and some of the photos looks exactly like the one i saw, guess i can confirm that it is indeed a burmese trout, Thanks for the Id Guys!!!