I haven't seen any fishing regulations, except for not being able to use explosives or electrocution. Up here in Isan I have had very little luck fishing in local ponds, lakes and even the Mekong. The application of nets is prolific, and even though the net fishermen are supposed to mark the positions of their nets with plastic ribbon, that never happens, so getting snagged in nets is fairly common.
The other problem I have seen is that as the fish stocks are becoming depleted, the local fishermen have moved to smaller and smaller net sizes, until they are catching the fry and further depleting the stock. There are a fair amount of the pay fishing ponds, and I have gone to a few, they are pretty spotty depending on how they are managed. If they just released a bunch of fish from the pens you do o.k., if not they charge you to fish but you catch nothing.
I have however gone to an upclass private fishing lake that the owner had stocked with rare fish from many different countries, including some record size predator fish, while it was not cheap, it was a blast!
Hopefully you'll do better than I have maybe the canals are the key!