First off, don't think of this as a show about fishing. It makes it sound boring. Just don't do that. Think of Tsuritama, rather, as a show about finding yourself, making new friends, and aliens. Yes. Aliens, who, by the way, control humans with water-guns. Now that sounds much more interesting and exciting, doesn't it?
At it's core Tsuritama is just a fun, simple, quirky little show.