The Environment Ministry says it's worried that illegal fishing could decimate walleye stocks in some waterways.

A northern Saskatchewan man has been fined $19,360 for illegally selling fish in what the government describes as a "large scale" operation.

Leon Morin of Buffalo Narrows received the fine after being convicted of unlawful marketing of fish caught by both commercial fishing and subsistence fishing, the Saskatchewan government said in a news release.

Morin has also been banned from commercial fishing for two years.

Morin pleaded guilty to four counts under Saskatchewan’s Fisheries Act and Regulations.

The government says he was charged after being caught selling fish out of season to uncover officers with the Environment Ministry.

The ministry had received reports since 2012 about abuse of walleye stocks taking place on a "large scale," the province said.

The walleye population has been decimated in other waterways and there was a concern that could happen again, impacting sport anglers, subsistence fishermen and legitimate commercial fishermen, the province said.

By law, fish vendors have to provide a receipt that includes the seller's name, address and licence number as well as the water body where the fish were caught and other details.