פירוש על עבודה זרה 75:4

Since small salted fish can be eaten raw, the laws of foods cooked by Gentiles do not apply.

R. Joseph states two laws about these little fish. First of all, if the non-Jew cooked them, the Jew may use them for eruv tavshilin. This is the meal that one begins to cook on erev Yom Tov, as if he is making it for Shabbat, that allows him to continue to cook on Yom Tov for Shabbat.
The second law is that if the non-Jew makes these fish into a fish-hash pie, the pie is prohibited because of the crust which was baked by the non-Jew.