Cook potatoes in salted boiling water until tender. Once cooked, pass through a potato masher or mash them anyway you can till smooth in a non reactive bowl.
Mix well the potato, tuna, 1 egg, ketchup, salt and pepper.
Heat the oil in a large skillet.
Whisk the other egg in a bowl and in another bowl add in the bread crumbs. Dip the croquettes in the egg first then the bread crumbs and pan fry till golden brown.
When cooked, place croquettes on a plate lined with paper towels to drain excess oil.
Serve immediately with ketchup.