Some fungus or baterial infection is going to happen whenever fish are handled and hauled. It's a fact of life no matter how careful the hauler was and how good the fish were from the source. What happens is they lose some of their protective slime layer or get a little beat up and a fungal or bacterial infection is the result. It you're only seeing a few fish like this I wouldn't worry about it.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.