In a message from David Bozsik I learned more about these fish:
Gambusia affinis are an introduced fish from the midwest and southeast U.S. I know when I began work on our pond, I wanted to have some fish, but I wanted native species. It is difficult to get any of the native fish around here any more. Almost all of the species are introduced, e.g., bass, bluegill, crappie, catfish, carp, etc. We did locate a supplier of one of my favorite species of natives, the stickleback. The local mosquito abatement is raising a small percentage of these fishes for mosquito control only in controlled habitats *garden ponds*. They have been wonderful in as much as they don't number in the thousands in about two weeks time, and are mainly benthic feeders (feed on the bottom). In a pond situation, they will maintain the mozzis as well. They haven't hampered the dragonfly or amphibian populations either. If you ever dry your pond out and refill and stock, try the three-spined stickleback. There might be some creeks nearby your area of the coastal range that would have them. They don't tolerate real warm water like the Gambusia though. I dug my pond with a 4 ft deep section so the fish (if needed) could descend deeper for cooler water in the summer. The willows we planted are now large enough that they provide the shade so that the pond doesn't get too hot."

I've also been told that Killifish, which are also natives, would be good. They feed primarily on the top surface of the pond and therefore won't eat nymph crawling around on the bottom or on the vegetation as Mosquito fish do, nor the Tree Frog eggs.

And maybe the best control of all are mosquito dunks, if you've tried them, please let me know how they've me. [kb] I've just started using them in a new 'washtub' pond on my front walkway. I bought them locally at The Pond and Garden Shop in Cotati, CA (Sonoma Co.).