Earthworms make great fish food, either whole for large fish , or cut up for smaller ones. You want to gather them where they haven't been exposed to pesticides though.
You can culture them, or get gather them from a compost pile or bin. Worm composting is usually done with a species that prefers it a little warmer, and reproduce faster than our domestic worms; but you can culture native worms the same as the others .
Use a medium made from torn up newspaper , a bit of peat moss and soil/fine sand. Feed them kitchen scraps ( peels, vegetable wastes, coffee grounds , tea bags)
Here is the link to a pdf about vermiculture.
http://www.organicagcentre.ca/DOCs/Vermiculture_FarmersManual_gm.pdf
You can also search on "Worm composting" for all sorts of links to worm sources and culturing "how to's"
Every year Vancouver and other communities sponsor a worm composting seminar with worms and composters available .