Hi Neo,
Sorry to hear that your L134 is not doing so well.

You say that it's mouth is up in the air have you noticed if it is breathing heavily. From the pictures you posted the fish appears to be healthy looking. I doubt that any disease/parasite could take hold that fast. Something appears to have gone wrong with the acclimatisation process and the fish is obviously stressed. Some more details would be useful in helping to isolate the problem.
Has your tank been set up recently and has it been allowed to fully cycle?
Have you tested your water parameters;ammonia,nitrite,PH etc.
What was the PH of the water at the shop where you purchased the fish and what is the PH in your tank.
In addition to the L134 were any other fish added to the tank?
I have had the very same thing happen to me with a couple of zebras, they were so stressed that they virtually lost all of their colouring. Luckily they pulled through.
I hope that your L134 pulls through, keep us posted on developments.
Adam