I would think a horse trough would be too narrow for such large fish... what are the dimensions? If you wanted to do that I'd go a bit smaller for fish. Also you'd need to clean it extremely well and get a pump/filter.
If you have room, I would get one of the round stock tanks. The largest one that my farm store has is 9' x 2'. If I calculated right that would give you roughly 950-960 gallons. http://www.gardenponds.com/cponcalc.htm
Are you planning to use one of those rubbermaid troughs? My sister works for rubbermaid and says that the rubbermaid troughs are lined with chemicals that can leach into the water and kill your fish. Just thought I would pass on the info
Rubbermaid makes stock tanks that are made for holding water for livestock to drink. Many people have kept fish and turtles in them without incident (myself included)
Are you planning to use one of those rubbermaid troughs? My sister works for rubbermaid and says that the rubbermaid troughs are lined with chemicals that can leach into the water and kill your fish. Just thought I would pass on the info