Personally I would use Mosquito Dunks as those conditions are not optimal for any fish. They are inexpensive and safe for pets and wildlife. They are easily found at Home Depot, garden centers and online.

None of them would live over the winter in your zone. Bettas and guppies are tropical fish and while goldish are not they still can't be outside over winter.

Here is a link that might be useful: Mosquito Dunks

I have been using dunks. I do have 2 ponds that I can transfer the fish in over the winter months but wanted to try fish instead of the dunks this year.

Thanks for the reply.

I kept my baby fish in a rubbermaid (small) container all summer till I donated them to a ponder in the fall. They grew and seemed ok. They are goldfish. They were newborns so they were very tiny at first.

Also I had no aeration but kept water hyacinth and a few other plants in the tub so they could hide and whatnot.

How big are these tanks? Without filtration, you should have 50-100 gallons per goldfish. Goldfish clean up mosquito larvae. The tropicals won't survive.

There are fertilizers that you can use with fish. The label should tell you. I'd stick to something that you push into the potting medium. I wouldn't use anything that you pour into the water.

A lot of people just use mosquito dunks. I have used them, but I have also used a betta fish on occasion, moving it carefully (acclimating) from one to the next every few days. Bettas are very, very good at slinking around the pots in search of larvae. If not moved around, though, it will eventually run out of food source, and you'll need to feed it. You'll also need to bring him inside for the winter.

My betta always got a bit spoiled with the live food, though, and when I would bring him in for the winter, he would turn his nose up at the pellets. Had to feed frozen mosquito larva or blood worms.

The nice thing about bettas is that they have an auxiliary breathing systerm that enables them to live in lower oxygen conditions that other fish could not survive. That doesn't mean they should not have a clean and healthy environment, but they can do well in smaller spaces.

I would nix the idea of guppies, unless you get all males. They breed like rabbits. Like the betta, they would need to be brought inside during the cooler months.

Lol @ johnkr: as have mine. But certainly not in a 'decorative tank' which I think was buyorsell's point here :)

@ladylotus: How much care/time are you willing to invest in the fish? If your foremost concern is mosquito control, stick with the dunks. If it's fish you desire, I'm afraid I can't offer any help...I see you're a gnat's wing away from the Great White North & waaay out of my experience zone. Here in the Deep South, rosy red minnows would be a good choice.

blessings,
~digger

i would go with the fathead minnow, of which the rosy reds that digger mentions, are a color variation. they are commonly sold as bait fish across the country. they might be winter hardy in your area since their native range includes parts of canada and west to utah.
rosy reds are prettier and i found some at a local pet store. they are short lived and can tolerate high temps, turbidity and stagnant water.

Here is a link that might be useful: fathead minnows

just wanted to thank Nancym for the Betta idea, I bought one for my big pot that has a water lily (I ran out of room last year in my pond for any more plants) and I love the little critter! Way more fun than pond dunks. He only spent a day outside 'cause it's still too cool at night. And he doesn't like the pellets so I have to catch stuff for him to eat, but I'm glad I sprung him from the fish prison at the pet store...

Remember yrs ago when the betta in a huge vase topped with a peace plant was the thing? My boss/2nd dad sent me one for my b-day. Flash took up residence in my aquarium when the fry moved to my puddle...lived way beyond his life expectancy and was my best bud for a very long time.

If a betta suddenly appears in my [now vacant] aquarium this weekend, I'm pointin the finger at you, Lexarose!

bless ya,
~digger

I agree with jeff-al, Fathead minnow though not as decorative as guppies and goldfish will keep your small pond clear of mosquitos, in a small tank with no aeration other than the plants, I would only do say 5 per tank, depending on your definition of medium, they would not survive the winter in a tank,the tank wouldn't survive winter outdoors either I assume. but you can donate them to a fishermen, or bring them in. Local pet stores in my area sell small Koi, very small, like goldfish small for $8-$15 or less, they will eventually get bigger though, which could be a good or bad thing I suppose! I am tempted myself, but they can live a long time!

I live in Tonopah(about 50 miles west of Phoenix), Az. and have 5 livestock water tanks. These range from 100 gallon to 400 gallon tanks. I have used goldfish in the past, but this year they all disappeared. No carcasses, no bones, nothing. None of my livestock eat them, so I wonder did they just get too hot? I would take some mosquito fish, if I knew where to get them. Any help?

Neverdun, they were likely gulped down by birds but mammals and snakes attracted by water would take them too.

" I would like to put in some fish to eat the mosquitoes. Do you have any suggestions?"

Mosquitofish
http://en.wikipedia.org/wiki/Mosquitofish

neverdun, I have plenty of goldfish if you need some more. I agree, the birds love to take them.

nina gretta
Where do you live in the valley? I can come and get some this week(probably Fri) we start school next week( I drive a school bus).

I'm on the east side of Tucson.

The OP is in zone 3/4 North Dakota where goldfish in decorative tanks are not going to survive outdoors in winter...

Of course they can in other locations/situations.

Personally, I think subjecting fish to less than optimal conditions (small volume, high temperature fluctuation, no filtration or aeration) when you can use an inexpensive non toxic control for mosquitoes isn't the right thing to do. I don't consider live animals disposable.

great information about bettas and goldfish. i think the previous poster needs to understand that guppies and goldfish are incredibly cheap, organic ways to control mosquitos while dunks are expensive, processed, dyed, bacteria that has a poor history of actually controlling mosquitos, at least in my yard. i have a lot of bromeliads, and those dunks don't work at all when ground and distributed. what a waste of $20!
for my future garden pond, one betta fish (approximately $3) which will eat mosquitos and produce fertilizer. win win. and if a bird eats it, there are goldfish at Petsmart for 16 cents each.

Here is a link that might be useful: Olde Scrubland Vantage

I personally would go with the mosquito fish I have been using them for years. They reproduce every 45 days and multiply by the thousands. Then I just spread them out. The large ones are the females and the smalls are the males. Just make sure to get some of both. The females also have a black dot on their bellies. This is the most efficient and cheapest method trust me. Plus they will overwinter in a 2 1/2 ft deep pond in zone 6. I have 9 ponds 7 rain barrels and a pond in the greenhouse. I swear by these fish and you don't have to feed them. One dozen will do the trick.

Here is a link that might be useful: Gabelmans Gardens blog

NeveDunnRanch,

I live in Az too..but I live on the east side Miami/Globe area,..if your temperature drops to freezing at any point, your fish freeze too! We do get snow here for only about 2 weeks... but everywhere around us has snow longer!..still the temperatures stay below freezing...until spring.you would have to figure out how to heat your water tanks for the fish to survive, most mosquito fish do not live more than a year maybe year and a half in slightly warmer conditions only indoors do they last approximately 3 years, guppies last a very long time indoors but they do breed like rabbits, and most other mosquito fish,will breed every 45 days or so, I myself own livestock and have to keep other water loving predators out that want to eat eggs or fish, for livestock I have to hook up a warm water line to have for my livestock...but I ended up having to catch the fish and bring them in for the winter..which prolongs the survival rate on the fish and I don't have to buy new! There are no mosquitoes during winter..and I know it's easier to keep them in the water, but they won't last!

THEY are NOT an indigenous species so by law in Arizona you cannot dump them in any lakes or rivers or anything other than what is acceptable to Arizona fish and game guidelines! there's only two places to get them and Arizona fish and game will guide you to where you need to go but most of the people that have them for their pawns, Arizona fish and game take certain information from you..before you can get them..Arizona puts them out in the water canals or flood zone areas of watering farmland and where livestock drink but if we are caught putting them in lakes and river beds stuff like, it's a BIG fine the fish populate so fast they will kill out our own natural indigenous species so Arizona fish and game take all the information down to pick them up if you bring a container you can bring home as many as you can carry in that container there's another person that has them she sells them and I believe she takes the information to and Arizona fishing game will direct you to her too if need be depending on where you're at on the map!

You can contact me for more info by my e-mail margaretmr2014@gmail.com..I work for the local FD..and a lawfirm in Phoenix, so I keep up with most fish&game regulations....and try to help as much as I can.

MOST IMPORTANTLY....MOST IMPORTANTLY...IF YOU LIVE IN A MOUNTAIN TERRAIN..You will have to stop on your way up back home BECAUSE every so many feet up/miles up..the elevation changes and the pressure becomes harder on the fish and their bladders will burst and you will have dead fish on your way home not many will survive so you have to stop every 10 minutes and weight about half an hour 45 minutes and then travel 10 more minutes and wait another 45 minutes so their bladders do not pop otherwise you wasted time and or money! and another thing the fish will eat the babies the parents will eat the babies if they are confined together in a tight spot so you want to try and separate the babies to keep them safe if you want to make sure you have enough and not buy anymore I have 1 male to three females and I have more than enough babies and I'm going to start selling them now because they do have about 60 babies each time!

Good luck...have fun...

Ladylotus,

What zone are you in? If you have any weather that drop below freezing the fish will not survive and if they are in tanks in freezing weather they will freeze so fast that's unbelievable you have to have them in something that stays deep and away from the elements if you have them in tanks which are normally made of plastic or glass the fish will freeze outside you would have to bring them in if you want to know more information I have put a lot of information down below further you can read that information and if you want to contact me my email information there too good luck