plecostomus?

some people on the pond forum have kept plecos in with their koi. they do need to come in when it gets cold, as far as i know.

I was thinking Pleco also. Not really meant for cold water, however it may slow down metabolism and growth. A pond is good because common ones grow to 18". It is most likely a tropical variety, they are hardy but risk of disease is higher in water parameters other then reccomended. Check out the link for ID. Maybe that sight can guide you better. The guppies "may" get eaten (or just attacked) by the barbs. Barbs are semi-aggressive, guppies are peaceful "community fish". I did keep them together as a kid with no problems but keep an eye out for aggression if you don't deside to seperate (reccomended) them.

Here is a link that might be useful: planet catfish site

If you didn't pay much for it, it is probably a common pleco. Hypostomus punctatus.

Here is a link that might be useful: common pleco info