When his son is kidnapped, an overprotective father must go on a long and tough journey to find his son.

They're clownfish!

This needs to be clear from the logline.

This works - character, event and action are all in place! However, it would be nice to get something about why this journey is meaningful for the father - "must face his fears" or something along those lines. Also, the repetition of the word 'son' makes the read a tiny bit clunkier - try changing it to 'him' or 'child' the second time.