hi stella
good to see there is someone on the spot
also good to know the brief salt dip works, thanks for info
mudfish can damage all fins by pushing completely into fine gravel.
the streams on our property were once full of untreated rimu sawdust and runoff from this still filters through to waterways during wet weather, mind you though they are springfed as well.
there are amazing populations of galaxiids in waterways.
sawdust is from old rimu mill on property and is between 50 and eighty years old ( so basically a peat substrate, but the water running in streams is springfed so very clean,) thats why i raised the question of filtration on the system
sorry i can't be of more help as have only had one problem with a very large giant that had fin rot, i suspected dirty water and temp too hot from being in tank inside so i increased filtration and did a 50 percent waterchange 3 times every 4 days, fish was clear of problems in 14 days
returned to stream when cleared up
good luck with the muddies