Protein digestion starts in the where denatures proteins.

The answer to this question would be: Stomach(gaster), HCl

Protein digestion happens in the stomach. The stomach will secrete the acid which was HCl to kill bacteria inside food and denatures the protein. The acid also activates pepsin enzyme and in turn, will digest the protein into smaller amino acids.

That is true! many fish species traveled to the u.s. because of it.