1 lb Skinned fillets of mackerel
-or sierra
Juice of 6 or 7 large limes
-(1 1/4 to 1 1/2 cups)
2 md Tomatoes
3    Or 4 canned chiles serranos
-en escabeche
1/4 c  Olive oil
1/2 ts Oregano
1/2 ts Salt (or to taste)
Pepper

Cut fish into small cubes, about 1/2 inch, and cover them with the lime
juice. Set in the bottom of the refrigerator for at least five hours, or
until the fish loses its transparent look and becomes opaque. Stir from
time to time.