The concrete can be sealed if necessary. Also old concrete won't be as bad as newer concrete.

Another possibility is a flow through operation with trout and well water. With the vertical sides it won't warm up much. Concrete raceways as far as I know are not sealed.

I will see if I can find a publication from a presentation of Purdue University on converting manure pits to aquaculture tanks and will post the link here.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.