I often see , mainly older Thai men , fishing ? with small nets down the drains ...

What are they looking for ?

Catfish.

Could be mosquito larvae used to feed there fighting fish they keep in glass bottles.

Catfish ??

Fighting fish in glass bottles ... Where do they fight ? I know in the glass bottles...

I thought they were looking for dropped keys or other treasures

Well by net do you mean a throw net or just a small net on a handle like for a fish tank?

if the second one then yes mosquito larvae. The fish fight each other. Siamese fighting fish

http://en.wikipedia.org/wiki/Siamese_fighting_fish

small net .. So mosquito larvae for their fighting fish seems the right answer

Thanks

Catfish ??

I was serious, I have seen men pull up catfish out of the drains outside Buddies.

They migrate from their ponds now when it's raining and some end up in the drains.

cockroaches for deep frying

cockroaches for deep frying

The fried cockroaches are all farmed and delicious.

I saw one of those catfish crawling around outside my apartment yesterday. Had to pick him up and drop him back in the pond because he was blocked by a concrete barrier.