I don't see any scars or swelling on the photo.
If it acts stressed, may be the switch between the tanks was stressful, or the water between the tanks is significantly different, or your water is not cycled, or it is simply not right for this species, or maybe it is bullied, or stressed by too much light, or too much motion around the tank, or not enough DO, etc.
If you'd like a more or less complete troubleshooting guide to fish appetite and health issues, here is one I put together. It may give you ideas what to look at.
Also, a lot of this info is usually needed for any worthwhile attempt to help you troubleshoot your situation. The less we know on this list, the less helpful we are. For example with the info in your OP, we pretty much can be 0% helpful.
If I recall correctly, you don't measure your water for ammonia and nitrite, which cuts a LOT of ground from under any attempt to help you.
***
Water Parameters
by a liquid test tube kit, such as the API freshwater master kit:
-- ammonia, ppm
-- nitrite, ppm
-- nitrate, ppm (before and after water change)
-- pH of tank and tap (before and after water change)
-- is the pH steady?
-- dissolved oxygen (DO) or description of aeration and stirring
-- temperature
-- is the temperature steady? (no significant swings?)
-- carbonate and general hardness, KH and GH, by a liquid test
-- TDS, ppm
-- or a general indication of TDS or water hardness and salinity
Water Source and Water Change
-- municipal or private
-- disinfected by chlorine / chloramine or non-disinfected?
-- if disinfected, how is water conditioned before water change?
-- average water changes (WC) on tank:
how much
how often
Tank
-- size
-- length, width, and height
-- time of running
-- if the tank is new:
how long was the tank cycled?
how was it cycled?
Stock (all fish, not just sick ones)
-- what species
-- how many each
-- estimated size of each
-- how long fish in question have been in tank
-- how long tank mates have been in tank
-- tank mate interactions, any aggression?
-- wild caught (wc) or captive bred (cb)
-- dewormed or not
-- treated against other parasites or not
Filtration
-- type: canister, HOB, or sump?
-- size
-- pump flow, gallons or liters per hour?
-- how often cleaned
-- how cleaned
Diet
-- what is the fish fed?
-- how much
-- how often
-- what are the tank mates fed?
Disease Symptoms, etc.
appetite
lethargic
bloated
swimming pattern
spots (where on body)
fuzzy patches (where on body)
excess slime
distorted features
color change
cloudy or swollen eyes
prior health history
-- of fish
-- of tank mates
were fish quarantined before being added to tank?
did the tank experience any previous disease out breaks?
-- what were they?
-- when were they?
medications used
Photos
-- the entire tank
-- close-ups of the fish and problem areas
***
HTH.