Fry or any live bearer don't need heaters to survive.They just prevent infections from happening faster or at all.
You should read the pond section under unfiltered tub ponds. A couple of us are in the process of making these setups with just water and an established bacterial community.
No heater , no filter , fewer water changes .. . .regular food.
It is apparent that these live bearers breed better in this environment. No fatalities have been reported yet.
Take a look at this article on a FILTERED CONTAINER POND
I keep guppies in a pond on my patio. They were my first fish (aside from Valentine the betta, which I had when I was three) and have lived through the stupid mistakes that I made when I was first starting out. At first I had 2 females and 2 males and put them into the pond. Within a month I had tons of fry. After a few months it was winter time and I was at my mom's house. I arrived at dad's house the next day only to find a pond full of my poor dead guppies. It had gotten too cold, but I decided not to get more until next summer so that I wouldn't have the same problem again. After removing all of the guppies I pretty much ceased care of the pond. By spring I couldn't wait so I decided to get more guppies. I decided that it would be neccesary to clean the pond and while I was cleaning it I discovered 4 adult guppies that had survived from the time that they were fry. They had hidden and lived without any care. I was overjoyed and soon had tons of fry once again. They are still living to this day and breed like crazy. Some of the males' tails are truly unique and look like works of abstract art. You really have to see it to believe it.
- by Kendall Karcher
We always forget that these fish, when in the right environment can survive through generations!
They still have their hardy gene in them. It never gets erased!
They will be fine in a bucket of water. Maybe just put a plant in to filter out the nasties.
PS. Why don't you start your own unfiltered tub pond in your backyard?
All you need in a 10gal bucket, water, substrate and java moss/pennywort/hornwort (floating plants) and not forgetting the fish. You can test them on your culls or any guppy you don't like. Remember to cycle the bucket with filter juice!!!!