Fish-Boy: An Inuit Folk Tale by Vanita Oelschlager

He is part fish and part boy, and he asks the fisherman to be his father.  The fisherman is hesitant about that but when the fish boy shows him where the big fish are, he agrees.

Vanita Books and Net Galley let me read this book for review (thank you).  It has been published and you can grab a copy now.

When they venture to another island to fish, they are met with scorn.  They are especially mean to fish boy.  So he turns them into sea parrots.  When they leave, he reverses the spell but the ones that were mean don't change back.  After that, people treated him with kindness, which they should have done in the beginning.