looks like a Monogenetic trematodes(skin and gill flukes)infestation of Macrogyrodactylus polypteri or any number of similar flukes try a salt bath. Separately dissolve 5 tablespoons of common salt (NaCl) per gallon of water. Add 1/3 the solution to the transfer bucket, wait ten minutes and add another 1/3 wait 10 minutes add the other 1/3 . Keep an eye on the new fish and remove any at the first signs of distress. Leave them covered in the bucket for a further 15 to 30 minutes.Many public aquaiums widely use a saltwater dip for all their new freshwater arrivals, at full-strength salinity (35 parts per thousand), for ten minutes. A major reminder is that common salt (NaCl) doesn't affect the pH buffer, but "Marine" salt and so-called "Aquarium" salt do. A change in pH, rather than the salt itself, accounts for most of the stress in a salt dip,If your fish do show acute stress you'd remove it,Net them out and transfer them to the Q Tank. Hopefully they should have left behind most of or all their external parasites.(this will not eliminate encysted parasites)Then, give the new arrivals 24 to 48 hours to settle down. -Anne