DPP4 and type 2 diabetes mellitus: For example, peptides with dipeptidyl peptidase IV (DPP4) inhibitory activity have been produced from rainbow trout (Oncorhynchus mykiss) by-products [7], Atlantic salmon (Salmo salar) skin [5] and Sardine (Sardina pilchardus) [8], proposing their application as functional ingredients for preventing and controlling type-2 diabetes.