The fuzz is probably saprolegnia, it's common in fish that are weakened by another condition. You should google some pictures to make sure the look of it is consistent with sapro. As for the velvet, usually it is not concentrated in just one area. Darken the room and shine a flashlight on the fish--if it's velvet, you should see yellowy granules in between his scales.
In any case, I would do more frequent water change and re-evaluate his environment for possible sources of stress, such as poor water quality, strong current, temperature fluctuations, cold temperatures, etc.