After seeing hundreds of Chinese cantilever fishing nets in the backwaters, and none of them in use, I finally see one being used in Fort Cohcin. They only catch a few small fish, but it seems to be fairly efficient.
I stop a fish mongers and have a quick chat. The big fish in the front is an Indian Salmon, which costs INR600 (£7, $14). The biggest fish are at the back, and they are king fish. There are several restaurants nearby that will cook any fish you buy and bring to them. I might give it a try some time.