It is not Columnaris.
It looks like fungus and maybe a bit of excess mucous.
Fungus normally gets into damaged tissue. If the fish have been physically damaged by rough handling, then fungus can get into the wounds. Poor water quality can also allow fungus to gain entry into damaged tissue.
Excess mucous is normally caused by something in the water irritating the fish.
The best treatment for mucous is big daily water changes and gravel cleaning for 1-2 weeks.
Fungus can be treated with aquarium or rock salt. Use 1 to 2 heaped tablespoons per 20 litres. (Start with 1 and if no improvement after 24 hours, add a second spoonful). Keep the salt in tank for 1 week after the fungus has gone, but no longer than 4 weeks. It usually goes after 24 hours with salt.
Triple Sulpha might help too but try salt first if you have some.