Yes i would definately fridge him and hopefully that will enable him to pass the pebble.
The curved gills are a definate sign of stress so he is definately not happy.
You should leave hi in thr fridge until the pebble has been passed and his gills look normal.
You need a something like an icecream container ,pop some dechlorinated water in their and cover him with some thing to stop light and temperature fluctuations, you should place a spare bottle of dechlorinated water in the fridge for daily water changes.
Whilst he is in there you should remove all the pepplesfrom his tank, bare bottom or sand is best and easier to clean.
Hope this helps some, and i hope he passes his pebble.
good luck.