Hello,
I just joined your board. I was inspired to join by the article I read here on mosquito fish.

I have a 1200 gal. pond that'a mostly a water/goldfish pond. Many comets and plants and 4 young koi, (who are getting to big and will probably be adopted by a proper koi keeper) and untold numbers of mosquito fish.

This pond was here when we moved in and I was told they got the mosquito fish from the county vector control.

These little suckers are everywhere! I can't skim leaves, clean the pump pre-filter or vacuum it without them getting into everything!

And now I read they eat the fry and eggs of the other fish!

Should I try to get rid of them? We live in California so they won't be killed be winter temps.

If I do trap/net them how would I kill them humanly?

you really shouldnt kill your pets. Ask around to see if people want them. Its good that they eat the eggs and fry because it sounds like your pond is overcrowded already.

I'll try to see if anyone wants them, but I don't think they will.

These fish are not pets. The goldfish are.

I don't mind them eating the other eggs and fry as much as I mind how prolifically they, themselves, are breeding.

If I could somehow keep the mosquito fish to manageable levels without killing them, I'll let them stay.

Have you read my page at http://www.fishpondinfo.com/mosq.htm
I think there are links on the page to making traps to catch them. Also, from the aformentioned page is a trap plan Dwight sent me:

"Cut off the top of a 2 L soda bottle (with no cap on) about 1/3 of the way down and flip the top over so it sticks into the bottom. Drill a few holes in the base of the bottle to let water in, and tie a string to the base so you can pull the trap in. Put food (fish food, meat, bread) in through the top. Put this in the pond where it should float. Fish can swim in through the bottle neck but have trouble finding the way back out."

There are some predators you can add that may eat some including bullfrogs, orfe, etc. which are also not native to California and may be a problem (at least the bullfrogs are; they are lowering the native CA frog populations). Mosquito fish are not native to CA. They will eat the fry of your goldfish which is good to keep their numbers down but they'll also eat frog eggs and tadpoles (which the goldfish and koi do as well since they're not native either of course). It is very hard to rid a pond of mosquito fish if they're doing well (mine all died on their own that I used to have). If you can trap or even net some out, that may help reduce their numbers. The ones you catch can be donated back to the mosquito management people who stupidly use these fish when, in some cases, it's not prudent. Or, you can try to give them to other ponders. If you can't find a home, perhaps someone would want them to feed their aquarium predatory fish. If not, the simplest and hopefully least painful way (it does in fact cause some pain) to kill them is to put them in pond water in a ziploc bag and freeze it.

i guess you should add a bull frog or something.