I know this website is mainly For GT fishing but i thought this advice might be handy.
If you get the oppurtunity i would highly recommend fishing a freshwater impoundment.
I have personally fished one in bangkok and another not far from Krabi.
Bangkok is mainly stocked with mekong catfish and arent hard to catch if you have a guide, gear is relatively crappy there so if it is an option i would take my own, these catfish do pull hard.
The Krabi impoundment is definately a much better option for fishing and variety, stocking things from siamese carp to barramundi and giant arryapaima. the gear is also much better at the Krabi impoundment.
From what i can gather highly populated regions of thailand and popular Holiday destinations have had the surrounding ocean totally stripped of any worth while fish, so if your heading there just for a holiday and wouldnt mind having a fish i would suggest these impoundments but if your heading there on a fishing holiday i would put in alot more research and try find a more remote location.
Although the fishing is better at the Krabi impoundment the bangkok impoundment is where the seven seas shop is located so i love going there to stock up on my Jai Poppers.
Photo 1 Is a Giant arrypaima from the Ktabi Impoundment.
Photo 2, 3, and 4 are all photos from the Bangkok impoundment.
I hope i could have been of help
