Yes, a waterbutt (rain barrel), is usually fine to use for goldfish. However, if your area experience acid rain, or you live in a city, you should check the pH of the water to make sure it isn't too low (<5 is bad, >6 is best)
No. Like all members of the carp family, goldfish can survive in a wide range of water temps.
No, an octopus cannot survive outside of water because they require water to breathe and move.
Salt water, water that is too hot or cold or has chemicals in it
No, absolutely not! Brackish water has salt water in it and it will die because of that!
Goldfish need water to swim and breath in, not mud. There are some species of fish that have evolved to survive in mud but Goldfish are not one of those species.
Goldfish are very hardy fish and can survive a wide range of water conditions. It wouldn't surprise me if they were the last fish to die after a major tank/water problem.
Some species of goldfish can survive in 0-degree water, but most goldfish won't survive in water below 10 degrees C. The fish would probably survive a while but would eventually stop moving and die.
Water snails are aquatic creatures that rely on water to survive. They cannot survive for extended periods outside of water as they need a moist environment to breathe and move.
No, octopuses cannot survive outside of water for an extended period of time as they require water to breathe and move.
goldfish will survive in tap water but it is best to put a bit of chlorine control in the water plus you will need a filter if you want the water and tank to stay cleaner for longer :)
Goldfish cannot live in rivers, they are 100% aquarium fish. They do not have strong enough immune systems to live in the wild and they cannot survive the fall and rise of the temperaure outside year round. Also river water will be to rapid for the fish to swim in.
No, goldfish are best with goldfish with the exception of weather (dojo) loaches, bristlenose plecos, and apple/mystery snails.Although goldfish can survive in warmer water temperatures, they are a "cold water" fish and not a tropical fish.