The decline coincided with a compulsory catch-and-release scheme to help salmon conservation.
However, a council report said that was not the only reason for the downturn between 2015 and 2016.
A general reduction in interest in fishing, particularly with younger people, and increased regulations are also cited as potential causes.
Money generated from the Nith burgh fishery goes into the Dumfries common good fund.
Income last year was less than £8,000, compared with nearly £14,500 the previous year.
The cost of maintaining the fishery is about £20,000 a year, so the fall in income and season ticket sales - down from 52 to 28 last year - is said to be a cause for concern.
A council report said the compulsory catch-and-release scheme was a factor and a further fall in ticket sales has been predicted if it continues.
Councillors will be asked next week if they want to continue to ban the taking and killing of fish in 2017.
Alternatively, they could relax the restriction to allow two salmon to be taken per person per year, which the current conservation designation of the Nith would allow.
Income from ticket sales for the River Nith common good fishing in Dumfries has fallen by 45% in a year.