Fish oil is the fat or oil that's extracted from fish tissue. It usually comes from oily fish such as herring, tuna, anchovies and mackerel. Yet sometimes it's produced from the livers of other fish, as is the case with cod liver oil.
A piquillo pepper is a type of small red chili pepper with a shape similar to a triangle that is grown in Spain. It has a flavor that is slightly sweet and spicy, but it is not a truly hot pepper.
Stuffed peppers or pimientos rellenos are part of traditional Spanish cuisine, especially that of the region of the Basque Country. Usually piquillo peppers are used. The fillings vary from Mango cheese, to chicken or cod in a red sauce; chicken likely being the most popular recipe.