If you want to take the muddy taste out of a fish gut it straight away and throw it in a ice slurry
when you get home put a roasting tray in the bottom of the fridge with the rack in it to keep the fillets off
the bottom of the tray, fillet the fish and skin the fillet , lay the fillet belly down on the rack in the tray
Leave in the fridge for three to four days empty any water from the tray daily there should be plenty
I've been doing this for years with fresh water mullet otherwise you couldn't eat them
The water that drains out of the fillet will stink of mud that's why you remove it daily
I've also done it with fresh water barra ( 4 DAYS IS BEST )
Cheers