Question
I live in Nova Scotia and have an outdoor below ground pond. It's a fiberglass tank about 4'x8' and 3 1/2' deep. I have goldfish which seem to overwinter alright. I was wondering if there are any bottom feeders that would be alright overwintered in a tank this size? The common everyday ones sold in pet shops seem to be for indoor aquariums only where the temperatures don't drop that much. Any suggestions?

Answer
Your pond is about 800 US gallons.  Most bottom feeders that people want to control algae are tropical fish.  If you just want a fish that stays on the bottom but doesn't necessarily eat algae, you can chose from some native catfish for example.  Most of those, when larger, will eat small fish.  The most commonly added "bottom feeder" is the plecostomus that eats some algae but they die below about 50 degrees F.  What did you have in mind?  I have a page on US fish (yes, I know you don't live there but it's the closest thing to what info you need on my web site) at http://www.fishpondinfo.com/misc2.htm
Good luck!

Robyn