Some Quick facts from wiki
Ernakulam refers to the eastern, mainland portion of the city of Kochi in central Kerala, India and has lent its name to the Ernakulam district. The Kerala High Court, the Office of the Corporation of Kochi and the Cochin Stock Exchange are situated here.
Since the Periyar River, Kerala’s longest, flows through all the taluks except Muvattupuzha. Also the Muvattupuzha River and a branch of Chalakkudy River also flow through the district. I am sure there will be plenty of Fishing spots in Ernakulam to share with others.
I will start off by mentioning one that i know.
Its Mulavukad, To be precise its just opposite of Mulavukad Bus Stop https://goo.gl/maps/8fAKDqYfcNP2
Please join this Discussion by adding more.
Last minute addition: Places where you can buy fishing gear, From my knowledge are Lulu Hypermarket https://goo.gl/maps/HUYNwDgCaY42 & Fishing Tackle India https://goo.gl/maps/BfbdjwmNTLQ2
But if you want to cut down on the cost, a bamboo stick and the type of string used on local made necklaces ( You can get them from any fancy store nearby at very cheap rate) will go the job!
If you live in a urban jungle and have never seen a bamboo growing nearby, Edappally is the place to go.