Never seen that before but I'd start off with the basics until someone can correctly ID the Problem. Until then do a massive water change, bump the temp up and add salt. I'm just guessing here because I've never seen that before but It could either be a bacterial infection or some other irritant causing the fish to produce excess slime but I'm not sure if excess slime would cause the deterioration of the fins so I'd lean towards a bacterial infection. Some water parameter numbers would help but either way start off with the water change, temp bump and salt.