He wanted everyone around him to see the mermaid he became friends with, but to them it only appears as a fish. That connects to the conflict or the problem. The boy wants everybody to believe that there are mermaids. However he fails to do so and is tortured and brain washed. The world he lives in does not allow the freedom of thought(shown in the very first part of the film) and to the people that live there except for the main protagonist, a mermaid is a mythical unreal creature which causes all of the chaos happening. At the end from my perspective the boy seemed like he had been given the death penalty.
