That's kind of a flip statement.
First of all, where are you going to find "fish chow"? Also, wolves and wild dogs don't regularly "fish". Even arctic dogs subside on wild hare, mice, etc. for a large portion of their diet (watch the movie "Never Cry Wolf" from 1983 - Charles Martin Smith stars, or read the book by Farley Mowat).
Second, major pet food companies work hard to ensure their formulas cover all a dog's daily intake needs as far as calories, fiber, vitamins, and minerals. It's in their best interest.
In the wild, our dogs' wolf cousins subsist mostly on small game with occasional takedowns of a large animal. They eat the stomach contents of these animals as well, which includes grains/grasses that the prey consume. In this sense, having grain mixed with commercial dog food, in fact, MIMICS what they'd get in the wild.
The best thing is to look for a name brand commercial food that doesn't have grain as a huge percentage of the diet. Also, I wouldn't avoid "by products" as a number of people do, because these are the parts of the prey that wild animals do eat, but we happen to avoid/abhor (unless you like bologna and hot dogs!).
In my example, Pro Plan offers a highly digestible lamb/rice formula that you can start with. Then, you can offer a change to chicken or beef as a variety. However, I think dogs crave that less than the fact they're getting a new, fresh bag. They can really tell the difference!
Good luck,
Walt