it's a bit hard to tell from the angle but there are definitely small white spots on the fish. If the water is clean and in good shape (no ammonia or nitrite and low nitrate levels), and it has no particulate matter in the water, then I would say it is whitespot and you should start treating asap.
Be careful what medication you use because catfish are sensitive to chemicals and don't tolerate full strength medications. Check the directions on the pack and use a lower dose rate if it says to for scaleless fishes like catfish and eels.
To work out the volume of water in the tank
measure Length x Width x Height in cm
divide by 1000
equals volume in litres
When measuring the height, measure from the top of the gravel to the top of the water level. If you have big rocks or driftwood in the tank, remove them before measuring the height.
Before you treat the tank do a 50% water change and complete gravel clean. This will reduce the gunk in the tank and allow the medication to work more effectively. It will also lower the pathogen count in the water and mean there are less nasties around to infect the fish.
Make sure any new water is free of chlorine and has a similar temperature & PH to the tank.
Remove carbon from the filter before treating otherwise it will absorb the medication out of the water.