Wikimecum:The best fish in Venice
The best place to go and buy fish is the Rialto Market. They have the biggest selection and best prices. You can also barter with many of the vendors towards the end of the market time, because they'll want to get sell as much of their fish as possible.
Location
The Rialto Market is located in the Campo San Giacomo/Campo della Pescheria in the sestiere of San Polo. If you are coming from Cannaregio, Castello, or San Marco, you'll have to cross the Rialto Bridge and then just walk straight for a few hundred meters. You will pass a lot of touristy stores, and just keep walking until you see a big open-air market on the right-hand side. From the Rialto Bridge, it is only a 2- or 3-minute walk. You will know when you get there because you will be able to smell the fish!
You can also take a vaporetto to get to the market. You will have to take either the #1 or #3 boat, and disembark at the Rialto Mercato stop.
