Each region has its own rules and regulations for fishing licences. There are three types of regional licences that are normally used. A license "tipo A" is for professionals, "tipo B" is for local citizens. A licence "tipo D" for foreigners costs about EUR 20 (EUR 9 for the license, EUR 11 stamp duty) for three months.
You can buy the State Licence at the Offices of the "Comune" in any Italian city. It's called a "Licenza di Pesca", but when you have one it doesn't necessarily mean you can fish anywhere you want. A special licence is required for all or most stretches of water. You can buy the "water licences" at local municipal offices or fishing shops.
Much easier and more productive is to fish in the sea (no licence required) or in any of the numerous private lakes that can be found with a bit of searching.
For example, Lago di Cavalieri near Pisa is a single lake mixed fishery that charges €7 per day.http
http://www.carp.com/article80.html?sid=a90b59ad9276cccebed996afddff0bc8
http://www.1fghp.com/italy.html
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