Gefilte fish are poached fish patties or fish balls made from a mixture of ground deboned fish, mostly carp or pike. They are popular in the Ashkenazi Jewish community.
In traditional recipes for gefilte fish, the fish is first deboned, often while still at the market. Next, the fish is ground together with eggs, onions and flour, matzoh meal or challah, and then stuffed into the skin of the deboned fish, giving it the name gefilte (filled or stuffed, compare the German gefüllte). The whole stuffed fish is then poached with carrots and onions. When prepared this way, it is usually served in slices. This form of preparation eliminated the need for picking fish bones at the table and stretched the fish further, so that even poor families could enjoy fish on the Sabbath.
Sometimes, gefilte fish are made in patties. The ground fish mixture is shaped into balls or oval patties and poached in a fish stock made from the head and bones of the fish. The poached balls are usually chilled and served with or without the jelled broth, accompanied by a horseradish-vinegar sauce known as chrain (either the red variety, flavored with beets, or plain white chrain, which has a sharper taste).
Gefilte fish may be slightly sweet or savory. Preparation of gefilte fish with sugar or black pepper is considered an indicator of whether a Jewish community was Galitzianer or Litvak. Traditionally, carp, pike, mullet, or whitefish were used to make gefilte fish, but more recently other fish with white flesh such as Nile Perch have been used, and there is a pink variation using salmon.
You can find authentic Koshar Fish on many Koshar Restaurants in Los Angeles