Authorities are investigating a mystery infection causing rashes and fungal growths on redfin in Lake Hume.
Russell Mason, of Compleat Angler Lavington, is collecting samples of the fish from residents for the Department of Primary Industry so they can look into it further.
He said the affected fish have a red rash and yellow growths along their scales, but the cause was so-far unknown.
"It's quite obvious when you see it," Mr Mason said.
"If you catch one, don't release it back to the water, take it out and freeze it and throw it out on bin night.
"Our fisheries have asked for people to drop off any affected fish [to the store] as we're trying to get samples for them."
A Department of Primary Industries spokesman said they were aware of a suspected fungal infection among fish from Lake Hume and were on working with Victorian authorities on the matter.
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He advised ulcerated fish should not be consumed.
"Suspicions of disease should be reported on the national 24 hour Emergency Animal Disease hotline 1800 675 888," he said.
"Samples of fish for disease testing should be kept chilled (not frozen).
"Please note that photographs while useful, cannot be used for disease diagnosis and laboratory confirmation would be required."
Mr Mason said of 120 fish he'd caught recently about two had been infected so estimated the disease could be affecting one in 100 fish in Lake Hume.
"It's concerning," he said.
"You don't like to see any diseases going through fish especially after the year we've had, we've had such ridiculously high numbers of fish.
"It's the best year a lot of people have seen in living memory, one of the best years ever."
Mr Mason said anyone who catches infected fish can drop them off at 343 Wagga Rd, Lavington.