Response to your third post:
1) There is no excuse and he cannot take such a plea.
Collect information / details of lease (of pond given by him to farmer) and mark copy of complaint to Fisheries Department also alongwith municipal corporation (for illegal use of land)
2) Yes, you can. Better take services of Lawyer from your place.
It depends on his experience and goodwill, cannot say.
3) Collect all the material pertaining to lease of pond to fisheries, lease to farmer, photos of pond etc., photos and videos with date and time will be of utmost importance, they will support your case.
4) It depends on the pendency of cases before the concerned court.
Depending on the priority of cases, it may take some where around 5 to 10 years (tentative).
He cannot take excuses, when he has let out the pond for commercial use and raising revenue / earning profit. Whatever, plea he takes he has to support / substantiate it with material proofs.
You have got a very good case, use all proofs you have and collate further proofs / evidences as many as possible to support your case.