Ah, the good old canoes versus kayaks debate...
Too bad you did not do any search about the origins of canoe polo because then you would have found out that canoe polo (or polo as the people who love the sport call it) originates in Europe. In Europe paddling in general (be it in open canoes or kayaks) is referred to as "canoeing".
Both open canoes and kayaks are called "canoes" overhere.
So there you have your answer. It is called canoepolo.
For more on canoe polo and its origins, history regarding rules etc. also check out https://en.wikipedia.org/wiki/Canoe_polo
Offtopic: To be honest, throwing a dead, rotting fish in someone elses boat sounds pretty disgusting to me.