Fishing probably does about equal to hunting, when the hunters are having a good year. This is with educated workers, but a well-placed hunting hut can get 1000-1200 a year (3 workers), while a normal fishing hut will get 1400 and upwards of 2000 a year (4 workers). Often the hunters get lower yields, like 600-800.
Gatherers are probably the best food source in the game, so they can't compare with that, but the main thing with fishers is that you are getting food from an area (rivers) that normally would do nothing for you. By having fishermen, you are getting more food than you otherwise would.
Of course, those workers can be spent elsewhere instead. But they are making more food than they eat, and comfortably so, so they're not a bad deal really, and I don't think they need "balancing".
If there is a balance issue in the game, it is that some people get firewood way too easily, and use it for trading, potentially giving them huge benefits. Lowering the trade value of firewood may as a result be needed. Otherwise I think the game is very-well balanced, and it seems like the testers have done a good job. Many approaches are viable. The start is tough, but once you get over that and learn what works quite well, it becomes much more manageable.
