Who did you sell the fish to? Why doesn’t anyone commercially fish anymore?
I was just a teenaged peon, working for what was called Grasteit Dakota Fishery out of New Town. The big city fish markets had a distributor who bought the fish from Grasteit by the truck load. I think the distributor was located in St Louis and they would distribute out to the fish markets in New York, Seattle, Los Angeles, etc. A lot of what we consider to be crap fish are very welcome by certain ethnic minorities (blacks, asians, Jews, etc).
I suspect the profit margins were a little on the thin side. If I remember correctly we were getting 6 cents a pound for uncleaned carp, about 40 cents a pound for gutted buffalo, and about a buck a pound for catfish with the other non-game species somewhere in between.
First and foremost, non-game species definition has changed over the years. Catfish are now a game species, as are paddlefish, etc. So that lessens the catch you can sell. Secondly, and probably most importantly, our approach of using 500-700 ft seines was only really successful from early May through late July. This is when you could find and catch carp and buffalo (98+ percent of the operation's catch) up in the shallow bays of Sak and Audubon, after that you start seeing them in large schools over deep water. On Sak we were primarily chasing Buffalo with one crew, and on Audubon the name of the game was carp with a second crew (I mostly fished Audubon). We'd keep some carp off of Sak but the ones in Audubon were a full 4-6 lbs heavier on average. You could catch over 20,000 lbs of fish in one good pull.
Come fall, the owners (Nephi and Leona) moved to Helena where they would fish for carp outside of ND's winter ice cover. So the limited season in ND is probably why you don't see a big commercial effort here nowadays. The effective season is just too short to make it profitable enough. At least, that's my guess although I think we've had some limited commercial efforts over the years in buffalo fishing on Jamestown Reservoir.
On a side note, public pressure also limited/stopped their use of gill nets to go after goldeye and white bass. All walleyes had to either be released unharmed, or if they died in the net you would have to pop their air bladder so they would sink. Bycatch of walleyes and northern pike were pretty minimal, like less than 10 game fish were caught on average with 10-20k pounds of carp. If you caught more than that, you probably didn't catch much carp and would just empty the net before the gamefish died.
While it did tend to pay pretty well for unskilled teenage labor, it is a less than sexy lifestyle. Work days could be from 0630-2300 for those who fished and hung around to process and get the catch tucked into the cooler. The smell of fish was with you always.