We've looked into buying property in France and it can be a minefield, let alone attempting to run a fishery as well!
If anyone wants a good insight into the pitfalls (and eventual rewards) of 'living the dream', keep a lookout for the Channel 4 program 'No Going Back.' (I think it's been repeated on cable/satellite). It follows a couple who sold their house in Surrey and bought a house and lake in Brittany, converting it into a fishery.
The effort involved is huge, as is the financial commitment. Due to the media coverage of this sort of venture, it may be that prices have inflated beyond that covered by selling your house in the UK. Prices in France have risen sharply in the last few years.
But remember, as Captain Sensible said, "You've got to have a dream, If you don't have a dream, How you gonna make a dream come true..."