Comments:
a. Most of the time here in the US the lakes are stocked artificially to keep the fish population at a fun level. Some of these little guys reproduce and maintain something approaching a stable population.
But you have to worry about whether this activity will continue post-peak, and if not, what kind of fish population will occur naturally.
b. One of the reasons there are plenty of fish, even little ones, is that there really aren't that many people fishing, in the grand scheme of things.
This source:
fishing stats
seems to suggest that there are 34 million fisherpeople in the US, which is not quite 15% of the population, but I would venture to guess that most of these go out only a couple of times per year. So, if fishing became a subsistence activity, a lot more people would have to do it and this would put pressure on fish population as they became a bigger part of the food chain.
Also note the decreasing number of youth 18 to 24 that fish. This does not surprise me personally. The average subscriber to Bassmaster magazine is 51.
c. Fishing is seasonal in a lot of places in the US. Better in spring, sometimes not worth a flip in the fall, ice fishing is not for everybody.
So if you are depending on this for a food source, better figure out a way to store and/or preserve your excess catch to tide you over on a lean day.
According to the depression-hardened elders in my family it was common if you had a good day to throw the extra fish into your rainwater collection system for a day or two until you get around to eating them.
d. I echo the above poster's comments on the issue of the fishing pole being a pretty inefficient way to catch fish. If there were a lot of people out trying to catch fish to live, there would be a lot more people using other lethal ways to do it. Example: shockers that will shock the little guys up, or poisons of various types. These weapons of mass fish destruction will put even more pressure on the fish population. Also, you have to ask the question post-peak about how good of a job the enforcement people will do in keeping the hillbillies from doing this sort of thing. It's kind of marginal right now.
e. One of the drivers of fish population is the amount of runoff from activities upstream, i.e. farming, that discharges stuff into the water that kills or promotes algae. Right now this is a problem in the midwest where all of the agricultural runoff is happening. This might be better or worse for fishing in a post-armageddon scenario. Also note that it might be easier for anyone who can keep a factory running to go back to their former polluting days (ex: cuyahoga river in the 70's) with minimal and/or corruption influenced enforcement of antipollution laws.
f. If you have a farm, and can build a farm pond, you can cut down on some of the suspense and adventure of this by maintaining your own little aquaculture. This is a fairly common practice in some parts of the country, such as Texas (in the years that they get rain). (In texas, they are called "tanks" for some reason.) If you can defend this little farm pond from poachers, and keep it from being overfished, you might even make a couple of bucks by charging people to fish there.
g. when it comes down to it, you are better off knowing how to fish, rather than not.
h. Example on TV from New Orleans: During all the rioting, when people were dashing out of the stores after looting the big screen tv's, etc. there was a picture of a guy carrying out a couple of fishing poles. We thought this was probably the smartest guy down there. At least he had a chance at an ongoing source of food.