How low of temps....

[Ron Sower]

....could I expect my zebra danios to survive in?  There are a few white clouds in with them too.  I have them in an outdoor 55g now and they have been surviving some extremely warm, shallow water until I got them into a non-leaking 55g over this weekend. I would like to leave them out over the winter.

Anybody got anything for me?

[BallAquatics]

Ron I've kept them in the upper 50's before without any problems.  Not sure what their absolute lowest temperature would be though.....

Dennis

[Ron Sower]

I may move the tank up close to the house and surround it with insulfoam sheets and see how it goes thru the winter.

[BillT]

Zebra danios if the temperature decline is not too fast can go down to something like 5-10˚C (41-50˚F). Their metabolism slows down so much they don't need to eat. They don't move much but stay upright. They can be kept like this for months.
Probably not good for them in the long run though. I would guess they would be more susceptible to disease (immune system turned off by cold).

I have seen this when research fish, being used as food for another research project animal (cuttlefish), were being kept in a cold room (with the cuttlefish) at 5˚C or so. Their water was clear and filtered, but I would think there wouldn't be much biofiltration going on at such low temperatures.

On the other hand:

A fast plunge into ice cold water (usually assumed to 4˚C) from their normal (lab) temperature range (22˚C (71˚F) to 28.5˚C (83˚F)) is considered a swift and relatively painless way to kill zebrafish.

Where I am (Eugene, Oregon (land of legal weed) and currently high temperatures), I would expect something above ground around here to freeze in the winter. That would probably not be good for them.

My goldfish do fine in an in ground pond (4.0 feet deep) over the winter. But they're goldfish (coldwater fish). The pond surface freezes a couple of times a year but not very deep.

You might be able to insulate a lot of it and also have it get heat somehow: black surface (to absorb heat from the sun), dryer exhaust?